JP3407525B2 - Image reproduction device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reproducing apparatus for controlling a background level in a full color digital copying machine.

[0002]

2. Description of the Related Art In a conventional full-color digital copying machine,
When the automatic exposure process (background level control) used in a black-and-white copying machine is operated in the color copy mode, the hue of the full-color copy is changed, so the automatic exposure process was operated only in the monochrome copy mode. With the automatic color selection (ACS) function that has been used in recent years, in order to reduce the operability of the copying machine and the copy time,
The copy operation can now be determined by automatically identifying whether the original placed on the original surface is a black-and-white original or a color original. As a result, it has become possible to automate the selection of automatic exposure processing during monochrome copying and not automatic exposure processing during color copying.

[0003]

However, when the presence / absence of automatic exposure processing is selected based on the determination result by the automatic color selection function, the following problems occur. Although demand for copying printed manuscripts such as newspapers and magazines is increasing, manuscripts with both color and black-and-white parts (printed manuscripts such as newspapers and magazines) are judged to be color manuscripts. The need to remove show-through was increasing. Furthermore, the background of manuscripts such as magazines has a slightly creamy background, and when a color copy was made, the background was faithfully reproduced in a cream color, which wasted toner consumption. In color copying, the function to improve copy quality by area discrimination processing such as black character discrimination processing after extracting the characteristics of the original has also improved, but it is not perfect, and the operator selects the original mode according to the original. And maintained the copy quality.
For this reason, the operator has made some kind of image adjustment to remove the color adjustment when making a color copy, but there is a problem that the operation is complicated. For example, when an operator makes a copy of a mixed black-and-white / color original, the copy machine once determines that it is in the full-color mode, and then sees the copy result that is output and shows the show-through or background fog.
The full-color copy mode was forcibly selected again, and some kind of image adjustment or original mode selection was performed to remove it. In this case, the automatic color selection function introduced for the convenience of the operation and the reduction of the copying speed, on the contrary, makes the operation more complicated and takes the copying time. Further, in the image adjustment of color copy and the selection of the manuscript mode, there is a problem that the copy result is hard to be the same as the image of the operator. In addition, when the automatic document feeder is mounted on a copying machine, if a monochrome document and a color document are mixedly mounted, such image adjustment cannot be performed. There was also the problem that you could not select the mode.

It is an object of the present invention, whether in a color copier, whether the original is a black and white original or a color original.
An object of the present invention is to provide an image reproducing apparatus capable of automatically and optimally controlling the background level and gradation correction at the time of copying, as in the case of a black-and-white copying machine, thereby eliminating the complexity of operation and improving the copy quality.

[0005]

In order to solve this problem, not only is the background level adjusted so that the hue does not change even in the case of color copying, but also whether or not the original does not require background control like a photograph. Judgment is required. Further, even if a black-and-white area and a color area are mixed in the original, it is desirable that gradation reproduction be continuously processed without a feeling of strangeness.
For this purpose, the background level is adjusted so that the hue does not change even in the case of color copying, and the original is automatically judged whether it is black and white or color. It is desirable to automatically select the document mode (photo mode / standard mode) when copying a document. The image reproducing apparatus according to the present invention includes a conversion unit that extracts a lightness signal and a color difference signal from color input image signals (R, G, B signals) of three primary colors, and a histogram of an image from the lightness component extracted by the conversion unit. And a discrimination unit that discriminates whether the input image is a color image or a monochrome image from the histogram generated by the histogram generation unit, and a discrimination between the background level and the character level based on the histogram. Depending on the type of the image, the brightness gradation correction unit that performs gradation correction on the brightness signal separated by the conversion unit, the color difference signal extracted by the conversion unit, and the brightness gradation correction unit A re-conversion unit that converts the lightness signal and the R, G, B signals of the three primary color information again, and a first calculation unit that creates a reproduction color signal necessary for full color reproduction from the re-converted R, G, B signals. Reconverted R, G,
A second calculation unit that creates a reproduction color signal necessary for monochrome color reproduction from the B signal, and two kinds of reproduction signals from the first calculation unit and the second calculation unit based on the type of the image discriminated by the discrimination unit. And an image reproduction unit that reproduces an image by selecting any one of the above. Preferably, an edge detection unit for detecting an edge portion from the color input image signals (R, G, B signals) of the three primary colors is further provided. Then, the histogram generation unit creates a histogram of the image from the lightness components other than the edge portion detected by the edge detection unit, which is extracted by the conversion unit. As a result, the analysis accuracy of the histogram of the achromatic portion is improved, and more appropriate image processing can be performed.

As described above, in the image reproducing apparatus, when the original information is copied, both the color copy and the black and white copy are made compatible, and the background level is automatically and optimally controlled. First, in order to determine the document type, the lightness component and the color difference component are separated from the R, G, B signals obtained by digitizing the document information with a color signal, and a histogram of the lightness component is generated. Based on this histogram information, the original type (color original and monochrome original),
While determining the document type (black and white / color and photo / standard), the background level and character level of the document are determined. Based on these judgment information, the background processing is corrected only for the lightness signal separated from the R, G, B signals depending on whether the original is a color original or a black and white original. In the case of a color original, the corrected lightness signal and the separated color difference signal are converted again into R, G, B signals, and reproduced signals C, M,
Create Y and Bk. In the case of a black-and-white original, a black-and-white reproduction signal is created. As a result, the background processing and the like are uniformly processed in the image reproduction of the color original and the monochrome original. Preferably, the apparatus further comprises a manuscript type discriminating unit for discriminating whether the manuscript is a photographic manuscript, and the lightness gradation correction unit is configured to automatically perform the gradation when the manuscript type discriminating unit judges that the manuscript is a photographic manuscript. No correction processing is performed. In this way, the original mode (standard original / photographic original) is automatically determined, and the background processing is not performed in the case of a photographic original.

[0007]

Embodiments of the present invention will be described below with reference to the accompanying drawings. (1) Overall Configuration of Digital Color Copier FIG. 1 shows the overall configuration of a digital full color copier. The document is read by the image scanner unit 30 and signal processing is performed by the digital signal processing unit 10. Printer unit 20
Receives a signal from the digital signal processing unit 10 and prints an image corresponding to the original image on paper in full color. Document reading by the image scanner unit 30 will be described. The document placed on the platen glass 31 is pressed by the pressing plate 39. When an automatic document feeder (not shown) is mounted, the document is thereby fed onto the platen glass 31. A document on the platen glass 31 is illuminated by a lamp 32, and reflected light from the document is reflected by a mirror 33.
After passing through a, 33b, and 33c, an image is formed on the linear full color sensor (CCD) 36 by the lens 34, converted into red (R), green (G), and blue (B) components of full color information, which are then transmitted to the signal processing unit 10. Sent. The scanner motor 37
Driving the first slider 35 at the speed V,
The second slider 40 mechanically moves at V / 2 in the direction perpendicular to the electrical scanning direction of the color sensor to scan the entire surface of the original. A white plate 38 for shading correction is provided at the edge of the platen glass 31.

The signal processing unit 10 electrically processes the read signal, and magenta (M), cyan (C), yellow (Y),
The black (Bk) components are decomposed and sent to the printer unit 20. The C, M, Y, and Bk image signals sent from the signal processing unit 10 drive-modulate the semiconductor laser 214 according to the image signal level in the semiconductor laser drive (PHC unit).
The laser light is the polygon mirror 215 and the f-θ lens 21.
6. The photosensitive drum 206 charged by the charging charger 207 is scanned through the folding mirrors 217a and 217b to form an electrostatic latent image.

The developing unit is composed of C, M, Y, and Bk developing units 208a, 208b, 208c, and 208d. The developing units 208a, 208b, 208c, and 208d are in contact with the photosensitive drum 206, and the photosensitive drum 206 is in contact. The electrostatic latent image formed above is developed with toner. On the other hand, the paper feeding unit 2
Papers fed from 01a, 201b, and 201c are wound around the transfer drum 202 by the suction charger 204 and conveyed to the transfer position by the timing roller 203,
The toner image developed on the photosensitive drum 206 is transferred onto a sheet by the transfer charger 205. One component of C, M, Y, and Bk is sent to the printer unit 20 for each document scanning in the image scanner unit 30, and one printout is completed by a total of four document scanning (frame sequential). Transfer method). 218 and 219 are reference position sensors for the transfer drum. In this way C, M, Y, Bk 4
After the color toner images are transferred in sequence, the separation charger 2
The paper is separated and conveyed by 09a and 209b, and the paper is separated from the transfer drum 202 by the separation claw 220. The sheet passes through the fixing rollers 210a and 210b and is discharged to the tray 211.

(2) Processing of Image Signal in Signal Processing Unit FIGS. 2 and 3 show the overall configuration of image processing in the signal processing unit 10. The image scanner unit 30 forms an image of the reflected light from the document surface on the linear CCD sensor 36 by a micro optical system, and photoelectrically converts it into R, G, B color separation information 40.
Obtain an analog signal of 0 DPI. These signals are sent to the signal processing unit 10. The A / D converter 100 is a CCD
The image data of 400 DPI photoelectrically converted by the sensor 36 is converted into 8-bit (256 gradations) digital data for each color information of R, G, B by the A / D converter. The shading correction unit 102 removes the white plate 38 for shading correction independently for each R, G, B in order to eliminate unevenness in the light amount of reading R, G, B data in the main scanning direction, prior to reading the original. The read data is stored in an internal shading memory (not shown) as reference data, converted into an inverse number, and then multiplied by the read data of the document information to correct shading. Interline correction unit 1
Reference numeral 04 indicates white data by using an internal field memory (not shown) according to the scanning speed (scaling ratio on the sub-scanning side) in order to match the reading position in the scanning direction of each R, G, B sensor chip. Is controlled in a line unit to output R, G, B data. The timing control unit 106 includes a CCD sensor 36, an A / D conversion unit 100, a shading correction unit 102, and an interline correction unit 104.
Control the timing of.

R output from the line correction unit 104,
For the G and B data, the scaling / movement control unit 108
Using two line memories for scaling for each G and B data,
The input / output is alternately performed on one line, and the write timing and the read timing are independently controlled to perform the scaling / movement control in the main scanning direction. A histogram generation unit 110 (see FIG. 5) generates a lightness signal from the R, G, B data after line-correction obtained from the scaling / movement control unit 108 and creates a histogram of the original. From the obtained histogram information, automatic color selection judgment to judge the color / monochrome of the original, judgment of the original background level to automatically skip the background level of the original, and copy operation original mode (standard / photo mode) Is automatically set.

The HVC converter 114 temporarily converts the R, G, B data from the scaling / movement controller 108 into a lightness signal (V data) and a color difference signal (Cr, Cb data). Editing processor 1
Upon receiving the V, Cr, and Cb data, 16 performs an editing operation such as color change or coloring by closed loop area detection based on the designation of an optional editor. The image interface unit 120 receives the V, Cr, Cb data sent via the first image selector 122 and transfers the image data to an external device. In order to support various color signal interfaces of image data, the image interface unit 120 uses the V, Cr, Cb signals to the R, G, B signals and the general-purpose color space X, Y, Z signals and L *, a *. , b * signal and the like for output to an external device, or conversely, for converting image data transferred from the outside into V, Cr, Cb signals. Further, C, M, Y, Bk transferred to the printer unit 20
Data can be transferred to an external device, and C, M,
It also has a function of receiving the Y and Bk signals and transferring them to the printer unit 20 side.

The image synthesizing unit 124 includes the second image selector 1
After selecting any of the V, Cr, and Cb data output from the image interface unit 120 or the edit processing unit 116 via 26, image combination (embedding / character combination) with the document data from the HVC conversion unit 114 is performed. To do. The HVC adjustment unit 128 has a lightness (V: brightness), a hue (H: hue), and a saturation (C: for the V, Cr, and Cb data from the image composition unit 124.
For the purpose of performing image adjustment corresponding to the human sense of "vibrancy", adjustment is independently performed for each of H, V, and C based on the designation of the operation panel. The AE processing unit 130 controls the background level of the document for the lightness component based on the information obtained by the histogram generation unit 110. Inverse HVC converter 1
32 again performs data conversion from V, Cr, Cb data to R, G, B data.

In the color copy mode, in the color correction unit 134, the LOG correction unit 136 firstly reconverts R, G, and
While converting the B data to the density data (DR, DG, DB), in the monochrome copy mode, the monochrome data generation unit 138 creates the brightness data from the R, G, B data, and then the gradation data for monochrome reproduction ( DV) is generated. The undercolor removal / blackening processing unit 140 determines the difference between the maximum value and the minimum value (MAX (R, G, B) -MIN (R, G, B)) of the R, G, B data in the document saturation information. And the minimum value of DR, DG, and DB (MIN (DR,
DG, and DB)) as an original under color component, performs the under color removal, blackening processing according to their values, to create DR, DG, C _O from the DB data, M _O, Y _O, the Bk data . The masking calculation unit 142 performs masking calculation processing for color correction,
C after under color removal processing, M, Y density data _{(C O, M O, Y} O) a C for color reproduction in accordance with the color toner of the printer unit 20,
Convert to M, Y data. The color data selection unit 144 outputs DV data as a monochrome copy mode when it is determined to be monochrome by the operation panel designation or ACS determination,
In the full color mode, according to the reproduction process signal (CODE), the masking calculation process data (C, M, Y data) is used during the C, M, Y reproduction process, and the black printing process data (Bk data) is used during the Bk reproduction process. Select and output.

On the other hand, the area discriminating unit 146 determines the minimum value (MIN (R, G, B)) and the difference between the maximum value and the minimum value (MAX (R, G, B) -MIN) from the R, G, B data. (R, G, B)), the discrimination such as the black character discrimination and the halftone dot discrimination is performed, and the result (JD signal)
And the correction data (USM signal) are output. Further, in order to achieve both the reproducibility of the image character area and the graininess of the image, a LIMOS signal for varying the image reproduction period is output to the printer side. The LIMOS signal sets the duty ratio for one pixel period of the signal output period (image reproduction period) to switch the gradation reproduction method. The MTF correction unit / sharpness adjustment unit 148 controls the input C, M, Y, Bk data by performing edge enhancement, color fringing correction, smoothing processing, etc. on the basis of the area discrimination result, to perform optimum correction of the copy image. I do. Furthermore, the γ correction / color balance adjustment unit 1
Reference numeral 50 denotes a γ curve, C, M, Y, according to the density level information input from the operation panel 154 according to the document type.
Adjust the Bk color balance. In this way, the C, M, Y, and Bk data that have been variously corrected are sent to the printer side for LIMO.
Transfer with S signal to obtain full color copy image of 400 DPI and 256 gradations. Here, the CPU 152 controls the signal processing unit 10, and the operation panel 154 performs input / output and display of data.

(3) Copy Mode Next, the copy operation mode of this full-color copying machine will be described. FIG. 4 is a basic screen on the operation panel 154, and the user can set various modes. (A) Undercoating (AE processing and manual setting) On the operation panel 154, it is possible to select whether to perform automatic exposure (AE) processing or manual designation (selection of 8 levels) for the undercoating. In the AE processing, five types of originals are judged from the original histogram information by the preliminary scanning operation (color standard (background white, with background color) / photo original and black-and-white standard / photo original). And
As shown in Table 1, if it is determined that the document is a color standard (white background) or a black and white standard document, brightness gradation correction (see FIGS. 12 and 13) is performed, and another document type (photographic document and color standard document) is corrected. (Underground color)), the center level specified manually is automatically set. When the manual is designated, data having the contents shown in Table 2 is output.

(B) Original mode operation panel 154 allows selection of an ACS (automatic color mode selection) mode or four types of original modes (manual designation). When the ACS mode is selected, one of the four document modes is automatically selected according to the document type determination by the preliminary scan operation (see Table 1). When it is determined that the document is a black-and-white document, one of the black-and-white standard mode and the black-and-white photo mode is automatically selected, and the black and white mode copying operation is performed by the black one-color reproduction process. If it is a color original, either a color standard original or a color photograph mode is automatically selected, and a copying operation is performed by a full-color reproduction process using four colors of C, M, Y, and Bk. The same applies to the manual mode (four original modes), but if the monochrome standard / monochrome photo mode is selected, the operation screen changes to the monochrome mode operation screen (not shown), and the monochrome gradation data is determined as the original parameter. Select the mixing ratio of R, G, B data. (In the ACS mode, the R, G, B average sensitivity distribution is set as the default in the manual mode, and the relative luminous efficiency distribution is set as the default.) Further, the reproduction color can be selected from 16 colors including black. In addition, a color separation mode that reproduces C, M, Y, Bk data for each document surface on paper, negative / positive inversion,
Create function for image creation and adjustment of base color and image erase, hue (hue) / saturation (brightness) / sharpness / γ correction (contrast light / dark) / color balance (RC / GM / B- There is an image quality adjustment function that simultaneously changes five types (Y / copy density) to simultaneously display a plurality of monitor images. In any case, detailed description is omitted.

(4) Histogram Generation by Preliminary Scan In the copying machine of this embodiment, the preliminary scanning operation is performed,
The result is analyzed to perform automatic exposure (AE) processing and automatic color selection (ACS) processing. In the image scanner unit 30, the original scanning unit is stopped on the side of the shading correction plate 38 opposite to the original reference position during main scanning before copying in order to shorten the first copy time. When the start button is pressed on the operation panel 154,
After the lamp is turned on, the shading correction plate 38 is moved to scan the correction data to scan it, and returns to the document reference position while creating the histogram data of the document. The automatic exposure process and the automatic color selection process are confirmed from the created histogram data, and the main scan operation is started.

Next, the histogram generation will be described. FIG. 5 is a block diagram of the histogram detection unit 110. The histogram detection unit 110 obtains a histogram of data in the document area during the preliminary scanning operation.
Before starting the preliminary scan, the histogram memories 202, 20
4 is initialized in advance, the CPU 152 writes “0” in the addresses of all the gradation levels (0 to 255) in the histogram memories 202 and 204. From the R, G, B data (8 bits) input from the interline correction unit 104, the brightness creation unit 200 calculates a brightness signal (VH) based on the following equation, and this is the first histogram memory 2
02, is input to the second histogram memory 204 as an address.

## EQU1 ## VH = 0.31640625 * R + 0.65625 * G + 0.02734375 * B (1) The lightness signal obtained by this equation is approximate to the human visual acuity (brightness). Here, the target of the histogram creation is not the R, G, B data but the brightness data VH, because the data separated into the brightness / color difference signals is corrected by the automatic exposure process. Will be described in detail.

Based on the sampling interval set value from the CPU 152, the sampling interval determination circuit 206 takes in the intervals (decimation rate) in the histogram memories 202 and 204.
To decide. This is because creating a histogram of all dots of the maximum document size (A3) requires a maximum memory capacity of 32 Mbits, and the memory capacity is reduced by sampling. FIG. 6 shows an example of the sampling situation in the histogram generation. Platen glass 3
When the document (hatched portion) placed on the No. 1 is read, the data at the position of the circle is sampled. Here, the sampling interval is appropriately thinned out (main scanning direction: 1/8, sub-scanning direction: 1/4) to reduce the memory capacity to 1 Mbit. The document size is detected before the preliminary scan, and various signals are input to the sampling interval determination circuit 210 from the timing control unit 106. Here, the / HD signal (main scanning direction) and the / VD signal (sub-scanning direction) indicating the original size area are input to the sampling interval determination circuit 206, and the generation of the histogram is permitted only within the effective original area. Not not. It should be noted that / TG is a main scanning synchronization signal and has a cycle for each line. (In the present specification, a signal prefixed with "/" means a negative logic signal.) VCLK is a synchronous clock of image data.

The operation of the histogram is a read-modify-write cycle with 8 dots as one cycle,
The addresses of the histogram memories 202 and 204 indicate the gradation level (brightness), and the data indicate the frequency (number) of each gradation level. That is, the histogram memory 202,
When the address ADR is input to 204, the data (frequency) of the address is read, +1 is added to the data by the adders 208 and 210, and the data is again written to the same address. Upon completion of the preliminary scan, the CPU 152
Reads the frequency data of each gradation from the histogram memories 202 and 204. As will be described later, the contents of the automatic exposure operation, automatic color selection operation, document type determination, etc. are determined from the histogram data obtained in the preliminary scan operation.

Two types of histogram memories 202 and 204
Is provided for automatic color selection processing. In the first histogram memory 202, / WE is always "
At the L "level, writing is possible for all pixels. That is, the first histogram memory 202 simply obtains the brightness histogram of the document. On the other hand, the second histogram memory 204 stores the histogram of achromatic dots in the document. Therefore, the minimum value circuit 212 and the maximum value circuit 214 detect the MAX value and the MIN value of the input R, G, B data, and the subtraction circuit 216 calculates the difference between them. And the difference between them is a predetermined level.
When it is determined that it is smaller than (SREF), the writing of the brightness VH data to the second histogram memory 204 is permitted. That the (MAX value-MIN value) of the R, G, B data is small indicates that the document data is achromatic data. Therefore, in the second histogram memory 204, the histogram is calculated only for the achromatic data.

The automatic color selection and the determination of the original type are the first.
Based on the first and second histograms created in the first and second histogram memories 202 and 204, the process is performed as described below. As described above, the histogram is obtained for the lightness data VH obtained by converting the output of the linear CCD sensor 36 sampled in the document size area. Where h1 (n) is the first
The frequency data at the lightness level n of the first histogram created for the entire original in the histogram memory 202 is represented, and h2 (n) is the lightness level n of the second histogram created for the achromatic portion in the second histogram memory 204. Represents frequency data at. Various quantities can be analyzed from the two histograms (h1 (n), h2 (n)). In automatic color selection, as shown in FIG. 7, the number of dots in C = color area (n = σ1 to σ2) is calculated from the second histogram. (Here, dot means linear CC
It indicates each area of the document detected by each CCD element of the D sensor 36. ) That is,

[Equation 2]

Further, in determining the document type, the CPU
152 denotes each frequency (h
1 (n)) to each frequency (h
2 (n)) is subtracted to obtain the third histogram (h3 (n) = h1
(n) -h2 (n)) is created. This third histogram represents the histogram of the chromatic color portion of the document. Then, as shown in FIG. 10, both histograms h1 (n),
For h3 (n), the sum of frequencies G25 to G in six brightness ranges
20, G35 to G30 are required. (5) Automatic color selection processing (ACS) The automatic color selection mode identifies whether the original stacked on the platen glass 31 is a monochrome original or a color original, and automatically selects a copy mode (color copy or monochrome copy). ) Is a mode for determining. As a result, when it is determined that the original is a black-and-white original, the image may be reproduced in the reproduction process of only one color (Bk). For this reason, the copying speed is increased because it is not necessary to perform the reproduction process four times as in color copying. In particular, when using the automatic document feeder, even if a black-and-white document and a color document are mixedly mounted on the automatic document feeder, an appropriate copy can be obtained without the operator's awareness.

In the automatic color selection, the document type (color copy or monochrome copy) is discriminated from the ratio of achromatic color to chromatic color. Specifically, using S and C obtained from the histogram, the ratio of the chromatic color dots in the document is calculated,
I am deciding whether to make a color copy or a black and white copy. As described above, C is a color region (n = σ
1 to σ2), and S is the total number of dots in the document size. Therefore, C / S corresponds to the ratio between the number of chromatic color dots and the number of (chromatic color + achromatic color) dots. here,
If the ratio C / S is equal to or less than the reference value, the black and white copy mode is set because the chromatic color is small, and if it is larger than the reference value, the chromatic color is large and the color copy mode is set. In addition,
This determination of automatic color selection can be made by using the ratio of the number of chromatic color dots to the number of achromatic color dots, but by using the total number of dots (S) as the denominator, the influence of the original size can be ignored. .

FIG. 8 shows a flow of automatic color mode selection by the CPU 152. First, the histogram creation unit 1
10, the first and second histogram memories 202,
Let 204 create a histogram of brightness (step S
100). Next, both histogram memories 202 and 204
The above C and S are obtained from the histograms (h1 (n), h2 (n)) obtained by (step S102), and the ratio C / S is calculated (step S104). If C / S is larger than a predetermined threshold value (YE in step S106).
S), and set the color copy mode (step S10
8) If not (NO in step S110), the monochrome copy mode is set (step S112).

(7) Discrimination of Document Type Further, the CPU 152 sets the information (h1 (n), h2 (n)) in the histogram memories 202 and 204 and the automatic color selection (ACS) as the first stage of the automatic exposure (AE) process. ) Results (see FIG. 8), the following five types of originals (Table 1
Refer to). (a) Black-and-white photo originals (black-and-white photographs, black-and-white high-definition halftone printing, etc.) (b) Black-and-white standard originals (black-and-white characters, line drawings, etc., relatively white background) (c) Color photographic originals (color silver halide photographs) , Color high-definition halftone printing, etc.) (d) Color standard document (white background) (relatively white background including color characters and color line drawings) (e) Color standard document (with background color) (color background) (Documents with a)

As described above, the automatic color selection is also performed based on the histogram, but the document type is determined by analyzing the histogram using the result of this automatic color selection (see FIG. 9). The concept of determining the manuscript type is as follows. The color original and the black-and-white original are already determined in the automatic color selection described above, and if the ratio of the number of achromatic dots to the total number of dots is larger than the reference value, it is determined to be a color original (three types). Otherwise, the black and white manuscript (2
Species). Further, the photographic original and the standard original can be determined from the distribution of the histogram. The standard document is a document mainly composed of characters, and the histogram shows a binary distribution (having peaks on the white side and the black side) as shown in FIGS. Here, the case where the base is not white is also considered. If it shows a binary distribution, it is judged to be a standard manuscript, and if not, it is judged to be a photographic manuscript. Specifically, the number of dots in the density range (black side) is compared with the number of dots in the vicinity of white from the histogram, and if the number of the former is small, it is determined that the document is a standard document because the distribution is binary. In the case of a color standard document, the case where the background is white can be determined by this. If the original is a color original and not a color standard original (white background), it is necessary to distinguish between a standard original with a background color and a color photo original. It is determined that the document is a document, and if not, it is determined that the document is a color standard document with a background color. Specifically, it is determined by the difference between the maximum value and the minimum value in the histogram.

FIG. 9 shows a flow of the document type discrimination by the CPU 152. First, from the data h1 (n) and h2 (n) of the first and second histogram memories 202 and 204, the various sums of frequencies G25, G24, G23, G22, G defined next are given.
21, G20, G35, G34, G33, G32, G31, G
30 is calculated, and further, the background level a (the gradation level indicating the maximum frequency of the output data ID 0.4 or less in the second histogram memory 204) and the character level b (the output data ID 0.6 or more in the second histogram memory 204) are calculated. To obtain the gradation level indicating the maximum frequency (step S
200).

[Equation 3] As shown on the left side of FIG. 10, the brightness VH levels 0 to 25
5 corresponds to the output data ID, but these values are in the six ranges of the output data (0.2 or less, 0.2 to 0.4, 0.4.
.About.0.6, 0.6 to 0.8, 0.8 to 1.1, 1.1 or more), h2 (n) or h2 (n) or h3 (n) (= h1
(n) -h2 (n)). In addition, in FIG. 10, the range indicated by C, M, Y, R, G, and B indicates the existence range of VH in the corresponding color. The above-mentioned values of 0.2 and 0.4 are set corresponding to this existence range.

Next, photographs (a) and (c) and standard manuscript (b) and
In order to distinguish (d) from the standard document with a background color (e), a photograph document and a document with a background color are determined. First, it is possible to discriminate between a monochrome original ((a) / (b)) and a color original ((c) / (d) / (e)) based on the result of the automatic color selection (ACS) described above. Yes (step S202). If the determination result of the automatic color selection is color (YES in step S202), the flow advances to step S204 to determine the type of color original document (here, α2 represents a threshold value). First, the ratio of the sum of frequencies of output data (ID) 0.4 or more achromatic color and output data (ID) 0.2 or more chromatic color (corresponding to a portion other than the white background) to the total frequency (Sn) Is smaller (YES in step S204), there are many white background portions, so it is determined that the color standard original (base white) (b) is present (step S206). Regarding the image processing, in the background adjustment, automatic exposure (AE) processing is set, the document mode is set to the color standard mode, black character discrimination processing is set, and gradation reproduction switching processing is set (step S208). If output data (ID) is 0.4 or more achromatic color and output data (ID)
If the sum of frequencies with chromatic colors of 0.2 or more occupies a large portion of the total document frequency (S) (NO in step S204), the ratio of the sum of frequencies in the chromatic color frequency block is very high. Is determined (step S210,
Here, α3 represents a threshold value). Specifically, the ratio between the difference between the maximum sum and the minimum sum of the chromatic color frequency blocks G30 to G34 and the total manuscript frequency is calculated, and when this ratio is not very high (in step S210). N
O), the background of the color standard document is colored because the image data is not averaged over all brightness gradations
It is determined to be (a) (step S212). Regarding the image processing, the background adjustment is centered on the standard manual setting, the original mode is the color standard mode, the black character discrimination processing is set, and the gradation reproduction switching processing is set (step S).
214). Otherwise (YES in step S210)
S), the image data is averaged over all brightness gradations, so it is determined that the original is a color photographic original (c) (step S
216) Regarding image processing, the background adjustment is performed in the center of the manual photograph setting, the document mode is set to the color photograph mode, the black character discrimination processing is not set, and the gradation reproduction switching processing is not set (step S218).

On the other hand, if the discrimination result of the automatic color selection (ACS) is not color (NO in step S202),
The process proceeds to step S220 (where α1 represents a threshold value). If the achromatic color sum of output data (ID) 0.4 or more is small in the total document frequency (S) (YES in step S220), it is determined to be a black and white photograph (e) (step S222). Regarding the image processing, for the background adjustment, the center of the photograph manual is set, the manuscript mode is set to the monochrome photograph mode, the black character discrimination processing is not set, and the gradation reproduction switching processing is not set (step S224). Otherwise (NO in step S220), since there are many white background portions, it is determined that the document is a black and white standard document (d) (step S226),
Regarding the image processing, for the background adjustment, the automatic exposure (AE) processing is set, the original mode is set to the monochrome standard mode, the black character determination processing is not set, and the gradation reproduction switching processing is set (step S228).

Finally, the respective document type determination results are displayed on the basic operation screen (FIG. 4) of the operation panel 154 (step S230). Without this display, the user may be uncertain because the determination result of the document type is unknown. Therefore, by displaying the document type on the operation panel 154, the user can immediately understand the determination result. Through the above-described processing, it is possible to determine the document types (a) to (e) and set the image processing corresponding thereto. Table 1 shows the contents of automatic color selection (ACS), image processing mode and document mode for each document type. Also, Table 2
Indicates settings of the background processing in various modes.

[0033]

[Table 1]

[0034]

[Table 2]

(7) HVC conversion and HVC adjustment The copying machine of this embodiment converts the image data into HVC data for execution. The HVC conversion unit 114 includes a matrix calculator that converts R, G, B data into a color space signal composed of a lightness signal (V) and two kinds of color difference signals (Cr, Cb).

[Equation 4] The three attributes of color, which are hue, lightness, and saturation, are obtained as follows using V, Cr, and Cb signals.

## EQU5 ## Lightness (Value) = V Saturation (Chroma) = (Cr ² + Cb ² ) ^1/2 (5) Hue (Hue) = arctan (Cb / Cr) Converted to such signals V, Cr, Cb The reason for doing this is that by performing processing that is similar to the human sense, high image quality is realized and the processing that is performed later (image synthesis, automatic exposure processing, HVC adjustment) becomes easier.

The output of the HVC conversion unit 114 is transferred to the processing units after the image composition unit 124, and also the editing processing unit 11
At 8, edit images such as color changes. And
In the image synthesizing unit 124, the V, Cr, Cb signals output from the HVC converting unit 114 are temporarily stored in the delay memory 116.
And is synchronized with the image signal from the edit processing unit 118. Then, the image synthesizing unit 124 uses the delay memory 1
16 output data (V, Cr, Cb) and output data (V, Cr, Cb) of the edit processing unit 118 obtained through the image selector 126.
Image composition is performed with Cb). A typical synthesis method is
Although there are watermark composition, embedded composition, character composition, etc., detailed description thereof will be omitted.

As shown in FIG. 11, the HVC adjusting unit 128
Are provided for the image quality adjustment mode. The HVC adjustment unit 128 includes a matrix calculator 128a that receives the V, Cr, and Cb data and performs the following matrix calculation processing so that image adjustment can be performed independently for each H, V, and C signal. .

[Equation 6] Here, q is a saturation adjustment coefficient, and θ is a hue adjustment coefficient. These coefficients are output from the HVC adjustment control unit 129 and sent from the image quality monitor control unit by Mdata (3
(Bit) is used as a switching signal and selected from eight types of coefficient groups in real time with the image signal. In this way
Adjustments similar to those of humans are made to facilitate image adjustments according to operator preference.

(8) Automatic exposure process (AE) The background process will be described as an example of the image process according to the document type. Conventionally, in a full-color copying machine, the automatic exposure process may result in a copy having a color balance different from that of the original, so that the automatic exposure process is performed only in the monochrome mode. However, even in full-color mode, when processing such as black character discrimination is introduced and clear mixed black-and-white and originals are reproduced, the background level of the originals is automatically adjusted like automatic exposure processing to prevent show-through. The need for optimal control has arisen. In this embodiment, the human visual acuity
A brightness signal (VH) approximated to (brightness) is created, and histogram generation and document type determination are performed. As a result, automatic exposure processing is performed in which the original background level is automatically controlled and copied without changing the color tone of the full-color original and conscious of the black / white / color portion. That is, once the image signal is converted from the R, G, B signals into the V, Cr, Cb signals, the data is subjected to automatic exposure processing, and then converted again into the R, G, B signals, so that the full color mode is also set. By applying unique processing to the monochrome mode, it is possible to optimize the background level. Further, even in the full color mode, no processing is applied to the color component signals Cr and Cb, so that the color balance is not changed by the automatic exposure processing.

More specifically, the background adjustment is
It is performed by automatic exposure processing or manual setting. On the basic operation screen of FIG. 4, the user can select whether to perform the automatic exposure process or to select one of eight levels of manual designation. In the automatic exposure processing, five types of originals (color standard (background white, with background color) / photo original and black-and-white standard / photo original) are performed from the original histogram information by the prescan operation (see FIG. 9). As shown in FIG. 9, if the color standard original (white background) or the black and white standard original is used, the lightness gradation complementation as shown in FIGS. 12 and 13 is performed, and for other original types, the manual center level is set. Is automatically selected as the default.

The automatic exposure (AE) processing section 130 performs background removal based on the document type information obtained from the histogram obtained by the histogram generation section 110. Here, for the document types (b) and (d), a lookup table memory (AE table) 131 for the brightness V is set.
Using a, the brightness signal (V _out ) after the automatic exposure processing is obtained from the brightness signal (V _in ) before the automatic exposure processing by the following correction formula, and the brightness correction is performed. That is, for a black and white standard manuscript,

V _out = 256 * (V _in −b−8) / {(a−8) −b} (7) Further, for a color standard document (background white),

V _out = 256 * (V _in −8) / (a −8) (8) where a is the background level and b is the character level. In other words, as shown in FIG. 12, with respect to a black and white standard original, the background is removed, and at the same time, light characters such as pencil writing are darkened to make the copy easy to read. For this reason,
The brightness between a + 8 and b is expanded to 0-255, a + 8
The data V _in from below to b and above from b is discarded. On the other hand, in the color standard document, only the background is removed. For a color standard original, as shown in FIG. 13, the data V _in between 8 and b is expanded to 0 to 255, and the data above b is discarded. In this embodiment, the level for skipping the background is set to 0-8.

In the monochrome / color standard document, the background level a and the character level b are obtained as follows. The following values are obtained from the brightness histogram h1 (n) of the entire original document in the first histogram memory 202. First, in order to determine the background level of the original, n = 136 to 255 (ID 0.4
In the following range, the gradation level m at which h1 (n) has the maximum frequency is obtained. Then, a = m-8 is set, and the background lightness is set to 255. Similarly, in order to judge the gradation level in the original only in the case of the black and white original, the gradation level 1 for which h1 (n) has the maximum frequency is obtained in the range of n = 0 to 120 (ID 0.4 or more). Then, b = 1 + 8, and the brightness of the character portion = 0. The reason a = m−8 is that the histogram distribution near level m has a normal distribution with some variation, so that the variation is set to ± 8 and gradations near level m are reliably skipped. is there. Similarly, b =
The reason for setting 1 + 8 is to ensure that the gradation near level 1 is black. Further, the reason why the control is not performed by b in the color original standard mode is that the characters are not always black.

Here, since the color components of Cr and Cb are passed through (in the AE tables 131b and 131c, D _in = D
_out ), only the light and shade information (V) is controlled without changing the color information of the document. Therefore, the background level can be automatically adjusted without changing the color information of the color original. Color difference signal Cr,
The Cb component is not corrected (V _out =
V), the color balance is not lost. Furthermore, the manual setting set on the operation panel 154 (automatic exposure process cancellation)
In, it is possible to perform lightness correction for changing the background level value. This mode is different in black and white / color and photo / standard mode, and the manual setting value is 7 levels.
With ± 0 as the center, -1 to -5 is in the direction of the background, +
1 and +2 are designed to be in the wearing direction (see Fig. 4). For detailed settings, see color standard mode,
In the black-and-white standard mode and the photo mode, as shown in Table 2, manually set levels +2 to -5 are set.

When a single color area and a color area are mixed in one original, it is desirable that the gradation expression in the background processing is continuously processed near the area boundary without any discomfort. Therefore, in addition to the histogram analysis, the feature extraction of the input image is performed and the image area determination is performed. That is, the brightness / color difference signals are separated from the R, G, B signals obtained by digitizing the document information to obtain histogram information. Based on this histogram information, the document type is determined and A
The E processing unit 130 performs background processing for performing tone gradation correction on the selected full-color reproduction signal or black-and-white reproduction signal based on the image type identification result, and performs image reproduction according to the background processing. The background processing is not performed on the photo original portion. Here, regarding the color standard document portion, the formula (8) is used.
Tone correction is performed with the
Gradation correction is performed in (7). Since both expressions (7) and (8) are similar, even if a single color area and a color area are mixed in one original, gradation expression in the background processing can be processed continuously without a feeling of discomfort. become.

In the inverse HVC converter 132, in order to convert the V, Cr, Cb signals into the R, G, B signals again, the inverse matrix operation of the above-mentioned matrix is performed as follows to output R, G, B. .

[Equation 9] The above-described scan data processing is performed by converting it to lightness data, but by performing the inverse HVC conversion here, subsequent data processing such as color correction can be performed on the data of the three primary colors.

(9) Second Embodiment Next, a second embodiment will be described. As described above, in the above-described first embodiment, the achromatic color portion of the original is distinguished and the histogram is obtained for the achromatic color portion and the whole. However, the edge portion of a character or a line drawing may be judged as a chromatic color even if it is originally achromatic color, and the accuracy of the histogram analysis of the achromatic color portion is lowered. Therefore, in the second embodiment, an edge detection circuit is provided in the histogram generation unit to create a histogram for pixels in the non-edge portion,
Improve the accuracy of analysis. As a result, more appropriate image processing switching can be performed. The difference between the second embodiment and the above-described embodiment is only the configuration of the histogram generation unit shown in FIG. The histogram generation unit includes an edge detection circuit 220 and a negative logic AND gate 22 in addition to the circuit shown in FIG.
2 is added, and other points are the same as the circuit of FIG. Since various circuits for detecting edges in image signals that are continuously supplied are known, a description of a specific circuit of the edge detection circuit 220 is omitted here. As previously described for the histogram generator, two types of histogram memories 202, 204 are used for automatic color selection processing. A sampling interval determination circuit 306 determines a sampling interval from various input signals and outputs the signals at the time of sampling to the histogram memory 2.
Send to 02, 204. When the address ADR is input to the histogram memories 202 and 204 at the time of sampling, the histogram data of the address is read, and +1 is added to the data by the adders 208 and 210,
Write to the same address again. Histogram memory 20
Addresses 2, 204 indicate gradation levels (brightness), and data indicate the frequency (number) of each gradation level.

Next, the input data to the histogram memory 204 will be described. The edge detection circuit 220 inputs the lightness signal VH from the lightness creation unit 200 to detect an edge, and outputs the output signal E to one input terminal of the AND gate 222.
Send DGE. On the other hand, the minimum value circuit 212 and the maximum value circuit 2
14 is the MAX value and MIN of the input R, G, B data
The value is detected, and the subtraction circuit 216 obtains the difference between the two. Then, the comparator 218 determines that the difference is at a predetermined level (SREF).
When it is determined to be smaller, that is, when the color is achromatic, the output of the comparator 218 is sent to the other input terminal of the AND gate 222. The output of the AND gate 222 is
It is input to the / WE (write enable) terminal of the second histogram memory 204. The edge detection circuit outputs an L level signal at the non-edge portion, and the AND gate 222 outputs an L level signal when achromatic. Therefore, AND
The gate 222 outputs a signal when the non-edge portion is achromatic. That is, the second histogram memory 204 is
Writing is permitted in the case of the achromatic color of the non-edge portion, and a histogram of the achromatic color of the non-edge portion in the document is obtained. On the other hand, in the first histogram memory 202, / WE is always at “L” level, and writing is possible for all pixels. Therefore, the first histogram memory 202 is
Simply obtain the brightness histogram of the original. As described above, when the preliminary scan is completed, the contents such as the automatic exposure operation, the automatic color selection operation, and the document type determination are determined from the histogram data obtained by the preliminary scan operation. Since the specific operation is the same as that described in the first embodiment, the description here is omitted.

[0047]

The color copy and the single color copy are compatible with each other, and the background processing can be handled in a unified manner, and the background processing can be automatically performed even if the operator does not specify the background processing. Both automatic color selection mode and background processing can be achieved. Even if various originals are mixed and stacked on the automatic original conveying apparatus, the original type can be automatically determined and the optimum background processing can be performed for each. Further, by obtaining the histogram of the achromatic pixels only in the non-edge portion, the accuracy of image analysis by the histogram is improved.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing an entire digital color copying machine.

FIG. 2 is a block diagram of a part of a signal processing unit.

FIG. 3 is a block diagram of the remaining part of the signal processing unit.

FIG. 4 is a diagram of a basic screen on an operation panel.

FIG. 5 is a block diagram of a histogram generation unit.

FIG. 6 is a diagram showing a sampling situation in histogram generation.

FIG. 7 is a diagram showing various amounts obtained from a histogram.

FIG. 8 is a flowchart of automatic color selection.

FIG. 9 is a flowchart for determining an image type.

FIG. 10 is a diagram for explaining a relationship between a brightness signal and various signals (G25 to G35).

FIG. 11 is a block diagram of an HVC adjustment unit, an automatic exposure (AE) processing unit, and an HVC inverse conversion unit.

FIG. 12 is a graph showing a change in document brightness distribution before and after AE processing for a monochrome standard document.

FIG. 13 is a graph showing changes in the original lightness distribution of a color standard original (white background) before and after AE processing.

FIG. 14 is a block diagram of a modified example of a histogram generation unit.

[Explanation of symbols]

110 histogram generation unit, 152 CPU, 20
0 brightness creation unit, 202 first histogram memory for all pixels, 204 second histogram memory for chromatic colors, 208, 210 adder for integration, 212 to 218
Chromatic color identification circuit, 220 edge detection circuit.

─────────────────────────────────────────────────── --- Continuation of the front page (56) References JP-A-1-320869 (JP, A) JP-A-2-295364 (JP, A) JP-A-8-186726 (JP, A) JP-A-8- 251402 (JP, A) JP-A-8-251427 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H04N 1/40-1/409 H04N 1/46 H04N 1/60

Claims (3)

(57) [Claims] 1. Color input image signals (R, G, B) of three primary colors
Signal), a conversion unit that extracts the brightness signal and color difference signal, a histogram creation unit that creates an image histogram from the brightness components extracted by the conversion unit, and a histogram created by the histogram creation unit Below the histogram obtained by the discrimination unit that discriminates between images and black-and-white images, and the histogram creation unit.
A brightness gradation correction unit that distinguishes the ground level and the character level , and performs gradation correction on the brightness signal separated by the conversion unit according to the type of image judged by the judgment unit, and extracted by the conversion unit A re-conversion unit for converting the color difference signal and the brightness signal corrected by the brightness gradation correction unit into R, G, B signals of the three primary colors, and full-color reproduction from the re-converted R, G, B signals. A first calculation unit that creates a necessary reproduced color signal, a second calculation unit that creates a reproduced color signal necessary for monochrome color reproduction from the re-converted R, G, B signals, and the image judged by the judgment unit An image reproduction device that includes an image reproduction unit that reproduces an image by selecting one of two types of reproduction signals from the first calculation unit and the second calculation unit based on the type. 2. Color input image signals (R, G, B) of three primary colors
Signal), a conversion unit that extracts a lightness signal and a color difference signal, an edge detection unit that detects an edge part from the color input image signals (R, G, B signals) of the three primary colors, and an edge extracted by the conversion unit. A histogram creation unit that creates a histogram of the image from the lightness components other than the edge portion detected by the detection unit, and a determination unit that determines whether the input image is a color image or a monochrome image from the histogram created by the histogram creation unit, Below the histogram obtained by the histogram generator
A lightness gradation correction unit that distinguishes the ground level and the character level , and performs gradation correction on the lightness signal separated by the conversion unit, corresponding to the type of image judged by the judgment unit, and extracted by the conversion unit A re-conversion unit for converting the color difference signal and the brightness signal corrected by the brightness gradation correction unit into R, G, B signals of the three primary colors, and full-color reproduction from the re-converted R, G, B signals. A first calculation unit that creates a necessary reproduced color signal, a second calculation unit that creates a reproduced color signal necessary for monochrome color reproduction from the re-converted R, G, B signals, and the image judged by the judgment unit An image reproduction device that includes an image reproduction unit that reproduces an image by selecting one of two types of reproduction signals from the first calculation unit and the second calculation unit based on the type. 3. The image reproduction apparatus according to claim 1, further comprising a document type determination unit that determines whether or not the document is a photographic document, wherein the lightness gradation correction unit is the document. An image reproducing apparatus characterized in that when the type determining unit determines that the document is a photographic document, gradation correction processing is not performed.