JP2001209782A - Image pickup device and its method for photographing character - Google Patents

Abstract

PROBLEM TO BE SOLVED: To quickly obtain a high quality binary image. SOLUTION: This device has a character binarizing mode for photographing character information of an original, etc., and is provided with a lens optical system 200 for forming the image of subject light, a CCD 201 converting the object light subjected to image formation into an image signal, a binarizing device 217 which binarizes the luminance signal of the image signal and generates a binary image, an LCD 111 for designating the density level of the binary image when the device 217 performs binarization, and an operating part 221.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup apparatus and a character photographing method thereof, and more particularly, to an image pickup apparatus having a character photographing mode for photographing character information such as a document and a character photographing method thereof. It is in.

[0002]

2. Description of the Related Art Conventionally, when a document is digitized and stored, a scanner as a dedicated image input device or a scanner unit of a copying machine or a facsimile has been used. Such a scanner device includes a light source in the device, irradiates the document with light emitted from the light source, reads reflected light with a CCD or the like, and then binarizes and stores the image. In such a scanner device, since the light source and the optical system are always constant, brightness and unevenness caused by the light source and the optical system are constant, and correction is easy,
High quality binary images can be input.

On the other hand, recently, with the development of video cameras and digital still camera devices, there has been an increasing demand for character recognition of input images. In particular, recent digital still cameras have begun to be used for various purposes as portable information collection tools due to the increase in pixels and miniaturization. For text information such as documents, whiteboards, signboards, and advertisements, sufficient information can be obtained with black-and-white images or binary images.In the case of binary images, the storage capacity required for storage is very small, so the number of pixels This is advantageous when shooting images with many images. further,
The binarized image can be transmitted by fax or can be reused by character recognition.

However, when an image is photographed by a digital still camera, a bright part and a dark part are mixed in one image due to the arrangement of the light source and the dimming around the optical system. If the threshold is binarized, there will be some parts where the characters are blurred and invisible, and some parts where the background is binarized to black and the characters are crushed and invisible,
This is not a level that can be used for post-processing such as OCR.

[0005] As described above, digital still cameras have begun to be used as substitutes for scanners. However, when a binary image is created in a camera, there are specific problems such as those seen in images taken by the camera. In terms of battery capacity and the like, a high-speed and high-performance binarization method is required.

Here, a conventional typical binary image generating method will be described. For example, according to an electronic still camera disclosed in Japanese Patent Application Laid-Open No. 6-225317, a technique is disclosed in which image data of the entire screen is binarized with a single threshold to generate a binary image.

Further, according to the image binarizing apparatus disclosed in Japanese Patent Application Laid-Open No. Hei 7-212591, a histogram creating means for obtaining a histogram of luminance values from a multi-valued image, and a histogram in the image based on the histogram obtained by the histogram creating means. A representative pixel value detecting means for obtaining a value representative of a white pixel value and a black pixel value; and a threshold value for obtaining a threshold value for binarization from the white pixel representative value and the black pixel representative value obtained by the representative pixel value detecting means. A technique including a determination unit is disclosed.

According to the image processing method disclosed in Japanese Patent Laid-Open No. 9-233326, a luminance frequency is calculated for each block in a multi-valued image, a luminance frequency optimum area in the luminance frequency is specified, and the luminance frequency is calculated. Calculate the average luminance value of the optimal region, calculate a binarization threshold in block units based on the average luminance value,
A technique for calculating a binarization threshold value for each pixel by interpolating the binarization threshold value for each block, and for binarizing the multi-valued image using the binarization threshold value for each pixel has been disclosed. I have.

[0009]

However, in the electronic still camera disclosed in JP-A-6-225317, a binary image is generated by binarizing image data of the entire screen with a single threshold value. Therefore, the part where the character is not visible due to blurring and the part where the background is binarized to black and the character is crushed and cannot be seen are mixed, and a binary image of a quality suitable for post-processing such as OCR is obtained. There is a problem that it cannot be generated. Further, in the image binarizing device disclosed in Japanese Patent Application Laid-Open No. 7-212593 and the image processing method disclosed in Japanese Patent Application Laid-Open No. 9-233326, a histogram is obtained or a repetitive operation is performed. In addition, there is a problem that the binarization process requires time and high-speed binarization cannot be performed.

SUMMARY OF THE INVENTION The present invention has been made in view of the above, and has as its object to provide an imaging apparatus capable of obtaining a high-quality binary image at high speed and a character imaging method thereof.

[0011]

According to a first aspect of the present invention, there is provided an image pickup apparatus having a character photographing mode for photographing character information of a document or the like. A lens system for converting the imaged subject light into an image signal; a binarizing unit for binarizing the image signal to generate a binary image; Density specifying means for specifying the density level of the binary image at the time of conversion.

According to the invention, in the character photographing mode for photographing character information of a document or the like, the binarizing means converts the image signal according to the density level of the binary image designated by the density designating means. Binarization generates a binary image.

[0013] The invention according to claim 2 is based on claim 1.
In the present invention, the binarizing means changes a binarization threshold value at the time of binarization according to the density level of the binary image specified by the density specifying means.
According to the above invention, the binarization unit changes the binarization threshold value for binarization according to the density level of the binary image specified by the density specification unit.

According to a third aspect of the present invention, there is provided an image pickup apparatus having a character photographing mode for photographing character information of a document or the like, comprising: a lens system for forming an image of the subject light; Imaging means for converting the image signal into an image signal, binarization means for binarizing the image signal to generate a binary image, display means for displaying the image, and recording means for recording the image Generating binary images at a plurality of different set densities from the image captured in the character photographing mode by the binarizing unit, and displaying the generated binary images on the display unit. .

According to the above invention, an image captured in the character photographing mode is generated by the binarizing means at a plurality of different set densities, respectively, and the plurality of generated binary images are displayed on the display means. indicate.

According to a fourth aspect of the present invention, there is provided an image pickup apparatus having a character photographing mode for photographing character information of a document or the like, wherein a lens system for forming an image of the object light, Imaging means for converting the image signal into an image signal; binarization means for binarizing the image signal to generate a binary image; and specifying a density level of the binary image when binarizing the image signal with the binarization means. Density specifying means, a display means for displaying an image, and a recording means for recording the image, wherein the density of the binary image designated by the density specifying means A first mode in which a binary image binarized by the binarization unit based on a level is displayed on the display unit, and an image captured in the character photographing mode is subjected to a plurality of different settings by the binarization unit. Binary image with each density Generated is a plurality of binary images the generated having a second mode for displaying on the display means.

According to the invention, in the first mode, the binary image is binarized by the binarizing means based on the density level of the binary image specified by the density specifying means in the character photographing mode. While the image is displayed on the display means, in the second mode, the image captured in the character photographing mode is generated by the binarizing means to generate binary images at a plurality of different set densities, respectively. The value image is displayed on the display means.

The invention according to claim 5 is the invention according to claim 3.
In the invention according to the fourth aspect, when displaying the plurality of binary images on the display means, a partial area in each binary image is displayed. According to the invention, when displaying a plurality of binary images on the display means, a partial area in each binary image is displayed.

The invention according to claim 6 is the invention according to claim 5
The present invention further comprises an operation means for changing a partial area of each of the plurality of binary images displayed on the display means. According to the above invention, the operation means changes a partial area of each of the plurality of binary images displayed on the display means.

The invention according to claim 7 is the third invention.
7. The imaging apparatus according to any one of to 6, further comprising a selection unit that selects one or a plurality of images from the plurality of binary images displayed on the display unit, wherein the selected one or the plurality of the plurality of binary images is displayed. The binary image is recorded on the recording means. According to the above invention, the selection means selects one or a plurality of images from the plurality of binary images displayed on the display means, and records the selected one or a plurality of binary images on the recording means.

According to an eighth aspect of the present invention, in the character photographing method of the photographing apparatus for photographing character information of a document or the like, a step of designating a density level of a binary image, and a step of forming a subject formed by the lens system Converting the light into an image signal; and binarizing the converted image signal according to a density level of the specified binary image to generate a binary image.

According to the above invention, the density level of the binary image is specified, the subject light formed by the lens system is converted into an image signal, and the converted image signal is converted into the density of the specified binary image. Binarization is performed according to the level to generate a binary image.

According to a ninth aspect of the present invention, in the character photographing method of the photographing apparatus for photographing character information of a document or the like, a step of converting subject light imaged by a lens system into an image signal; Generating a binary image for each of the image signals at a plurality of different set densities,
Displaying the plurality of generated binary images on a display unit; and outputting one of the plurality of binary images displayed on the display unit.
Alternatively, the method includes a step of selecting a plurality of images and a step of recording the selected one or more binary images in a recording unit.

According to the above invention, the subject light formed by the lens system is converted into an image signal, and the converted image signal is converted into a binary image at a plurality of different set densities. The binary image is displayed on the display means, one or more images are selected from the plurality of binary images displayed on the display means, and the selected one or more binary images are recorded on the recording means.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a digital camera to which an image pickup apparatus and a character photographing method thereof according to the present invention are applied will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a top view of the digital camera according to the present embodiment. In the figure, reference numeral 101 denotes a mode switching button for switching between a natural image mode for photographing a normal natural image, a character mode for photographing a document and a white board, a character binarization mode, and the like.
Is a mode display unit that displays the mode (natural image mode, character mode, character binarization mode) selected by the mode switching button 101, 103 is a release for instructing shooting, 104 is a reproduction mode (reproduction), Shows dial keys for selecting a recording mode (recording), a data transfer mode (PC), and the like.

FIG. 2 is a rear view of the digital camera according to the present embodiment. In the figure, reference numeral 111 denotes an LCD used for monitoring an image, confirming a captured image or reproducing an image recorded in a memory, and 112 denotes an LC
LCD on / off button for turning on / off D111,
Reference numeral 113 denotes a button for setting various modes, 114 denotes a button for switching parameters in various setting modes, 11
Reference numerals 5 and 116 denote keys used for changing the zoom magnification at the time of monitoring, and for switching setting items when setting various modes.

FIG. 3 shows various setting mode screens when the photographing mode is the character binarization mode. 3 is displayed when the character binarization mode is selected by the mode switching button 101 and the photographing mode is the character binarization mode. 5 shows various setting mode screens displayed on the screen.

In the various setting mode screens of the character binarization mode shown in FIG. 3, "recording mode", "white balance", "exposure compensation", "focus", "density adjustment",
And each item of “binary image display” is displayed, and parameters of each item are set.

Next, a method of setting the parameter of "density adjustment" on the various setting mode screens of the character binarization mode in FIG. 3 will be described. In the various setting mode screens of the character binarization mode in FIG. 3, “Density adjustment” is selected using the keys 115 and 116 (indicated by diagonal lines in FIG. 3), and the button 114 is pressed. (Light, standard, dark, extraordinary) density adjustment parameters (density levels) can be set. FIG. 4 is a diagram illustrating transition of switching of the density adjustment parameter. As shown in FIG. 4, when the density adjustment parameter is set to “standard”, the button 11
Pressing 4 once results in "dark", pressing twice results in "special darkness", pressing 3 times results in "light", and pressing 4 times returns to "normal". As will be described later, the setting parameter x of the binary threshold (cb) of the binary threshold setting circuit 216 (see FIG. 6) is changed according to the density adjustment parameter to be set. Thereby, a binary image of the density level set by the density adjustment parameter can be obtained.

Next, a method of setting a parameter of "binary image display" on the various setting mode screens of the character binarization mode in FIG. 3 will be described. Using the buttons 115 and 116 on the various setting mode screens of the character binarization mode in FIG.
By selecting “binary image display” and pressing the button 114, it is possible to set the parameters of the binary image display in two steps (one image, four images). When “one image (first mode)” is set as the binary image display parameter, the density set for the image captured in the character binarization mode (the density set by the above density setting parameter) Only one binary image is displayed on the LCD 111.
The displayed binary image is immediately recorded in the memory 219 (see FIG. 6) in the digital camera.

Further, "4" is used as a binary image display parameter.
(Second mode) ", the image photographed in the character binarization mode is binarized at each of four levels of densities (light, standard, dark, and extraordinary) to obtain four images. A binary image is generated, a common part of the four binary images is cut out, and the screen of the LCD 111 is divided and displayed.
FIG. 5 shows the L of a binary image captured in the character binary mode when the binary image display number parameter is set to four.
5 shows a display example of the CD 111.

When the binary image display number parameter is four, the displayed binary image is stored in the temporary frame memory 209.
(See FIG. 6) but not yet recorded in the memory 219. In FIG. 5, keys 115,
By operating the button 116, the display area of each of the four binary images a to d can be moved. This allows the user to visually confirm the area of the binary image of interest. After visually checking, the user presses the button 113 to select the binary image on which the most appropriate binarization has been performed. The selected image is displayed with a thick image frame as shown in FIG. In the example shown in FIG. 5, the binary image c is selected.

Here, when it is desired to select and record only one image, after selecting one binary image, the release 103 is pressed and the binary image is recorded in the memory 219. When a plurality of binary images are to be recorded, the user selects a plurality of binary images and presses the button 114 to fix the image. The fixed image is always displayed with a thick frame. Another binary image can be selected by pressing the button 113 from the state where the binary image has been selected, and the button 114 is pressed to confirm the selection. After the image selection is completed, the release 103
Is pressed to cause the memory 219 to record a plurality of binary images.

FIG. 6 is a block diagram of a digital camera according to the present embodiment. FIG. 1 is a block diagram illustrating a processing system for a luminance signal of an image signal, and illustration and description of a processing system for a color difference signal are omitted.

As shown in FIG. 1, the digital camera 100 includes an optical system 200 including a lens system and an aperture for forming the subject light, a CCD 201 for converting the formed subject light into an analog image signal, and an analog image. AGC circuit 202 for adjusting signal gain, A / D converter 20 for converting an analog image signal whose gain has been adjusted to a digital image signal
3. White balance adjuster 204 for adjusting the white balance of the digital image signal, luminance signal generating circuit 205 for outputting the luminance signal of the digital image signal, aperture corrector 208 for performing the aperture correction of the luminance signal, luminance signal after the aperture correction Memory 209 for temporarily storing image data, an LCD control circuit 220 for controlling display of the LCD 111, an LCD 111 for displaying an image and the like, an exposure control circuit 210 for performing exposure control, and an unillustrated operation according to operation instructions of the operation unit 221. CPU 211 that controls the operation of each unit according to the program stored in the ROM.

Also, the digital camera 100 uses Ev0
A comparator 212 that compares (exposure amount determined from the brightness of the subject) and Ev (exposure amount calculated from an aperture amount and a shutter speed determined by an automatic exposure control program of the camera), and is stored in the frame memory 209. Block buffer 21 in which the obtained luminance signal is stored in block units
3. A non-low brightness pixel average value calculation circuit 214 for calculating a non-low brightness pixel average value, and a non-low brightness for setting a threshold when the non-low brightness pixel average value calculation circuit 214 calculates an average value of non-low brightness pixels A pixel detection threshold value setting circuit 215, a binary threshold value setting circuit 216 for setting a threshold value for binarizing the luminance signal by the binarization device 217, a binarization device for binarizing the luminance signal to generate a binary image 217, Compressor 21 for compressing binary image
8, a memory 219 for storing the binary image compressed by the compressor 218, the mode switching button 101 described above,
Release 103, dial key 104, LCD on / off button 112, various mode setting buttons 113, button 11 for switching parameters in various setting modes
4, an operation unit 221 having keys 115 and 116 and the like to give an operation instruction to the CPU 211, and a mode display unit 102 for displaying a mode.

As described above, the digital camera having the above-described configuration has a natural image mode for photographing a normal natural image, a character mode for photographing a document, a whiteboard, and the like.
It has a character binarization mode and the like.

FIG. 7 is a diagram for explaining the automatic exposure control program curve in the natural image mode, and particularly shows the relationship between the aperture and the shutter speed (Ev diagram). In the case of the natural image mode, the exposure control circuit 210 performs automatic exposure control according to the automatic exposure control program curve (thick line) in FIG. Specifically, first, when the brightness of the subject is determined, the exposure amount (Ev) is determined. Then, shooting is performed using a combination of the aperture and the shutter speed at the point where the straight line indicating the determined Ev intersects with the automatic exposure control program curve (thick line). In the figure, for example, Ev is 16
In the case of, the aperture is 16 and the shutter speed is 1/25
Set to 0 seconds. When Ev is 6, the aperture is set to 2 and the shutter speed is set to 1/15 second.

FIG. 8 is a diagram for explaining automatic exposure control program curves in the character mode and the character binarization mode, and particularly shows the relationship between the aperture and the shutter speed (Ev diagram). In the case of the character mode and the character binarization mode, the exposure control circuit 210 performs automatic exposure control according to the automatic exposure control program curve (thick line) in FIG.

In the character mode and the character binarization mode, it is assumed that the strobe is not emitted. The focal length f of the lens is 28 mm in terms of 35 mm film. When Ev ≧ 10, the automatic exposure control program curve is the same as in the natural image mode. Generally, the shutter speed at which camera shake does not occur is called the reciprocal of the focal length. In this case, since f = 28 mm, 1/28 second is the lower limit of the shutter speed at which camera shake does not occur. In the exposure control programs of the character mode and the character binarization mode, the shutter speed of 1/30 second is set as the lower limit (minimum shutter speed), and a program different from that in the natural image mode is set during 6 ≦ Ev ≦ 10. It is rare. If Ev <6, the exposure is insufficient because the aperture F is fixed at 1.4 and the shutter speed is fixed at 1/30 second. In such a case, as described later, the image signal is
A proper exposure is obtained by electrically amplifying in the C circuit 202.

Next, the operation from photographing to image recording when photographing in the character binarization mode will be described. A character binarization mode is selected with the switching button 101 of the operation unit, and recording is selected with the dial key 104, and the release 1 is selected.
When 03 is pressed, shooting in this character binarization mode is performed. First, in the optical system 200, the exposure control circuit 21
The aperture amount of the aperture is determined using the exposure information determined at 0. The CCD 201 captures an image at the shutter speed set by the exposure control circuit 210, converts the subject light formed via the optical system 200 into an electric signal, and converts the analog image signals of the pixels R, G, and B into pixels. Output.

The AGC circuit 202 includes an exposure control circuit 210
, The analog image signal input from the CCD 201 is electrically amplified and output. Specifically, A
The GC circuit 202 amplifies the image signal at a constant amplification factor when a proper exposure amount is obtained according to the exposure amount determined by the exposure control circuit 210, while the brightness of the subject is insufficient and the shutter speed is reduced. In the case of shooting in which the amount of exposure becomes insufficient at the minimum, the amplification factor is increased to obtain an appropriate level of output.

The A / D converter 203 includes an AGC circuit 202
The exposure control circuit 210, the white balance adjuster 204, and the CP convert the amplified analog image signal input from
Output to U211.

The exposure control circuit 210 is provided for the A / D converter 20
Calculate the average value of the digital image signal input from 3
The exposure amount is determined by setting the aperture amount of the aperture of the optical system 200 and the shutter speed of the CCD 201. The amount of exposure is determined by the optical system 200, the CCD 201, the AGC circuit 20
2, and output to the CPU 211 and the like, and exposure control is performed.

The white balance adjuster 204 has an A / D
The white balance of the digital image signal input from the converter 203 is adjusted, and the digital image signal whose white balance has been adjusted is output to the luminance signal generation circuit 205. Specifically, the white balance adjuster 204 detects an achromatic portion in the digital image signal, and when the achromatic color is R =
The white balance is adjusted by adjusting each color signal so that G = B.

The CPU 211 outputs to the comparator 212 the exposure Ev0 determined from the brightness of the subject and the exposure Ev calculated from the aperture and the shutter speed determined by the automatic exposure control program of the camera. Comparator 21
2 compares Ev0 with Ev and outputs the comparison result to the luminance signal selector 207 and the aperture corrector 208.

The luminance signal generation circuit 205 includes a luminance signal generator 206 and a luminance signal selector 207. The luminance signal generator 206 generates a broadband luminance signal YH and a narrowband luminance signal YL based on the white balance-adjusted digital image signal input from the white balance adjuster 204, and outputs the luminance signal. Output to selector 207. Hereinafter, a specific calculation method of the broadband luminance signal YH and the narrowband luminance signal YL will be described.

The broadband luminance signal YH is calculated by the following equations (1) to (3) when the target pixel is R, G, and B, respectively. YH_R = R (1) YH_G = G (2) YH_B = B (3)

The above-described luminance signal generation method is a method for generating a luminance signal having the widest band when the subject is monochrome. Further, for example, when a checkered RGB filter as shown in FIG. 9 is arranged in the CCD 201, the narrow-band luminance signal YL at G0 is calculated by the following equation (4).

YL_G0 = (4G0 + G1 + G2 + G3 + G4) / 8 (4)

The luminance signal YL at R0 and B0 is calculated by the following equations (5) and (6).

YL_R0 = (G0 + G1 + G2 + G5) / 4 (5) YL_B0 = (G0 + G1 + G3 + G6) / 4 (6)

As described above, using the surrounding G pixels,
By taking the average, a narrow-band luminance signal YL with little noise is generated.

Based on the output of the comparator 212, the luminance signal selector 207 outputs the narrow-band luminance signal YL when Ev is greater than Ev0 (when the subject is dark and the shutter speed is at the lower limit). Is equal to Ev0, a wideband luminance signal YH is selected and output to the aperture corrector 208.

The aperture corrector 208 receives the luminance signal (narrow band luminance signal Y) input from the luminance signal selector 207.
L or the outline portion of the broadband luminance signal YH) is corrected and output to the frame memory 209.

FIG. 10 is a block diagram showing a detailed configuration of the aperture corrector 208. Aperture compensator 20
8 is a vertical Laplacian filter 30 as shown in FIG.
0, horizontal Laplacian filter 301, absolute value circuit 30
2, 303, comparator 304, selector 305, adder 30
6 and a parameter section 307.

The result of comparison between Ev0 and Ev of the comparator 212 is input to the parameter section 307. If Ev is larger than Ev0, the band-pass filter coefficient of FIG. 11B is used, and Ev and Ev0 are equal. In this case, the filter coefficients of the high-pass filter of FIG. 11A are set to the vertical Laplacian filter 300 and the horizontal Laplacian filter. By using the band-pass type, even if the S / N of an image is reduced due to insufficient exposure, fine noise of one dot is suppressed, and not only the noise of the background is reduced, but also the quality of characters is improved. Can be.

The vertical Laplacian filter 300 calculates the vertical Laplacian of the luminance signal input from the luminance signal selector 207, and selects the selector 305 and the absolute value circuit 30.
Output to 2. Also, the horizontal Laplacian filter 301
Calculates the Laplacian of the luminance signal input from the luminance signal selector 207 in the horizontal direction, and outputs it to the selector 305 and the absolute value circuit 303.

The absolute value circuit 302 calculates the absolute value of the Laplacian in the vertical direction of the luminance signal input from the vertical Laplacian filter 300, and outputs it to the comparator 304. Further, the absolute value circuit 303 includes the horizontal Laplacian filter 30.
The absolute value of the Laplacian in the horizontal direction of the luminance signal input from 1 is calculated and output to the comparator 304.

The comparator 304 compares the absolute value of the Laplacian in the vertical direction with the absolute value of the Laplacian in the horizontal direction, and outputs the comparison result to the selector 305. The selector 305 selects the Laplacian having the larger absolute value, and
Output to In the adder 306, the luminance signal selector 207
And the Laplacian having the larger absolute value input from the selector 305 is added to the luminance signal input from the selector 305 and output.

Next, the luminance signal subjected to the aperture correction is binarized. The luminance signal subjected to the aperture correction by the aperture corrector 208 is temporarily stored in the frame memory 209.

On the other hand, since the image size is determined by the size of the CCD 201, the CPU 211 calculates the block size / shape necessary for the binarization processing and the sampling period based on the image size, and the CPU 211 The low-luminance pixel average value calculation circuit 214 is controlled.

FIG. 12 is a diagram showing an example of the sampling period. FIG. 3A shows a sampling cycle when the image size is small, and FIG. 3B shows a sampling cycle when the image size is large. Also, the uneven brightness of the image taken by the camera,
The area near the center of the image is bright and becomes darker toward the periphery. Therefore, the ROM 211 of the CPU 211 previously stores, for example, a combination of square, rectangular, and triangular blocks as shown in FIG. If you do so, the brightness inside the block will be more uniform and compared to using only square blocks,
Higher quality binarization becomes possible.

The CPU 211 calculates the frame memory 2 in units of blocks having a shape and size set in advance.
An image (luminance signal) is read out from the block 09 and temporarily stored in the block buffer 213. The non-low-luminance pixel average value calculation circuit 214 samples and reads out pixels from the image (luminance signal) stored in the block buffer 213 at a sampling cycle (see FIG. 12) preset by the CPU 211, and calculates the luminance value. Calculate the average.

FIG. 14 shows a non-low luminance pixel average value calculating circuit 21.
4 is a block diagram showing a detailed configuration of FIG. As shown in FIG. 14, the non-low luminance pixel average value calculation circuit 214 includes a gate circuit 400, an adder 401, an addition result register 402, a gate circuit 403, a shift register 404, and a comparator 40.
5, a counter 406 is provided.

The pixel values of the sampled luminance signal are input to the comparator 31 and the gate circuit 35. The comparator 405 compares the pixel value of the luminance signal sampled and read with the threshold thl_ij set by the non-low luminance pixel detection threshold setting circuit 215, and outputs the comparison result to the gate circuit 400 and the counter 406.

In the gate circuit 400, the pixel value is set to the threshold value th.
If it is larger than l_ij, the pixel value is output to the adder 401. In the adder 401, the value of the addition result register 402 and the pixel value are added, and the result is added to the addition result register 4.
02 is stored. At the same time, the counter 406 is incremented by one. Here, as a result of the increment, the counter 406 sets the addition result register 402 when the digit is raised (the counter indicates a power of 2).
Of the shift register 404 via the gate circuit 403.
And shift right by the number of bits indicated by the counter.
After processing for all the pixels in the block, the value stored in the shift register 404 becomes the non-low luminance pixel average value ave_
ij is output to the binary threshold setting circuit 216 and the non-low luminance pixel detection threshold setting circuit 215.

The non-low luminance pixel detection threshold setting circuit 215
The previous block (if the current block is (i, j), (i-
1, j)) non-low luminance pixel average value ave_i-1
The threshold value thl_ij used by the non-low luminance pixel average value calculation circuit 214 is calculated by multiplying j by a predetermined coefficient Ca. Assuming that the predetermined coefficient is Ca = 1/4, the non-low luminance pixel detection threshold value setting circuit 215 determines the non-low luminance pixel average value ave_i−
Since the value is obtained by removing the lower two bits of ij, no special circuit is required.

The binary threshold value setting circuit 216 uses the non-low luminance pixel average value ave_ij calculated by the non-low luminance pixel average value calculation circuit 214 to set a binary threshold value th_ij for binarizing an image. The calculated value is output to the binarizer 217. Specifically, the binary threshold value setting circuit 216 includes a multiplier for multiplying a predetermined coefficient Cb by ave_ij. For example, if Cb = x / 32 (x is a default value representing a natural number not exceeding the denominator), Since the binary threshold value setting circuit 216 can be constituted only by a multiplier, it is advantageous in terms of cost and speed.

X is a parameter setting screen in the binarization mode. When one image is set as the binary image display parameter, x is set in the parameter setting screen in the binarization mode (see FIG. 3). It is determined according to the density adjustment level (four steps) to be performed. For example, when the density adjustment level is “light”, x = 12, when the density adjustment level is “standard”, x = 16,
X = 20 for “dark”, x = 24 for “special”
Is set, and a binarization threshold th_ij based on the x is output to the binarizer 217. On the other hand, when four images are set as binary image display parameters on the parameter setting screen in the binarization mode, four coefficients Cb1 and Cb
b2, Cb3, and Cb4 are set. Four coefficients Cb1,
Cb2, Cb3, and Cb4 are each, for example, Cb
1 = 12/32 (light), Cb2 = 16/32 (standard setting), Cb3 = 20/32 (dark), Cb4 = 24 /
32 (very dark). The binary threshold setting circuit 216 calculates the four coefficients Cb1, Cb2, Cb
3, four binarization threshold values th_ based on Cb4, respectively.
ij is output to the binarizer 217.

The following binarization processing and recording processing in the memory 219 are performed by using 1 as a binary image display parameter (see FIG. 3).
The case where one image is selected is different from the case where four images are selected. First, the processing when one image is selected as the binary image display parameter will be described.

The binarizer 217 includes a binary threshold value setting circuit 21
The image of the above-described block is binarized using the binarization threshold th_ij input from 6 to generate a binary image, and output to the compressor 218. The compressor 218 performs a compression process suitable for binarizing a binary image such as MH, MR, or JBIG. The compressed image has a very small capacity and is stored in the memory 219. Since the binary image thus compressed has a very small capacity, a large number of images can be stored in the memory 219. However, JPE for compressing natural images
Two compressors, a G compressor and a binary image compressor, are required, which slightly increases the cost.

The compressor 218 may be used in common with JPEG compression used in natural image compression. In that case,
The compressor 218 becomes a JPEG compressor, and the binarized image is JPEG compressed. JPEG is a compression method used when recording a natural image. When a binary 8-bit image is compressed, the size after compression becomes larger than that of the above-described binary image compression, but a binary image compressor is not required. Therefore, there is an advantage that the number of parts is reduced and the cost is reduced.

At the same time as recording in the memory 219, the binary image is written back to the frame memory 209 as a 1-bit / 1-pixel image. The image written back to the frame memory 209 is subjected to resolution conversion by the LCD control circuit 220 in accordance with the number of display pixels of the liquid crystal, and is then displayed for, for example, one second. Is displayed for one second. With this display method, it can be determined whether or not the image has been properly binarized. After the binary image is displayed for a total of two seconds, the camera returns to the photographable state, and the LCD 111 displays a monitor screen.

Next, 4 is set as the binary image display parameter.
Processing when a sheet is selected will be described. The binarizer 217 binarizes each of the above-described block images using the four binarization thresholds th_ij input from the binary threshold setting circuit 216 to generate four binary images. That is, four output values are obtained for one pixel of the input image. These four outputs are respectively written back to different addresses of the frame memory 209 as an image of 1 bit / 1 pixel. When the binarization is completed, four binary images are stored in the frame memory 209. After the binarization is completed, the LCD control circuit 220 displays partial images (partial areas) of the four binary images according to the number of display pixels of the liquid crystal (see FIG. 5). Here, as described above, when the keys 115 and 116 are pressed, LC
The D control circuit 220 reads out different partial images (areas) of the four binary images from the frame memory 209, and
Displayed at 111. Then, the user selects and confirms one or more of the four binary images displayed, and releases
When 03 is pressed, the selected binary image is compressed by the compressor 218.
, And stored in the memory 219.

In the above description, the configuration in which the lens system does not include the zoom lens is described. However, the configuration may include the zoom lens system. FIG. 15 is a top view of a digital camera having a configuration including a zoom lens. In the figure, the same parts as those in FIG. 1 are denoted by the same reference numerals, and the description thereof will be omitted.

When the camera lens is a zoom lens, the focal length varies depending on the zoom magnification. In the figure, reference numeral 105 denotes a zoom switch. W
When the zoom switch 105 is tilted to the IDE side, the focal length becomes shorter in accordance with the time when the switch is tilted, and wide-angle shooting becomes possible. Further, when the zoom switch 105 is tilted toward the TELE side, the focal length increases according to the tilting time, and close-up shooting becomes possible.

If the lens is a 3 × zoom lens with f = 28 mm on the WIDE side, f = 85 mm on the TELE side. FIGS. 16 and 17 show f = 56 mm (intermediate zoom) and f = 85 mm (T) in the character mode and the character binarization mode.
The automatic exposure control program curve (thick line) at the time of (EL-side zoom) is shown. The exposure control circuit 210 is provided in FIG.
Exposure control is performed according to the automatic exposure control program curve (thick line) shown in FIGS. In the case of a zoom lens as shown in FIGS. 16 and 17, the lower limit shutter speed (minimum shutter speed) is set according to the change in the focal length. As a result, it is possible to perform photographing with no camera shake at any zoom magnification. Here, the zoom lens has been described, but the exposure control can be performed for the bifocal lens in the same manner.

As described above, according to the present embodiment, when shooting in the character binarization mode, the “binary image display” of the various setting mode screens (see FIG. 3) in the character binarization mode is used. When "one image (first mode)" is selected, the binarizer 217 converts the image signal according to the density adjustment level set on the various setting mode screens (see FIG. 3). Since binarization is performed to generate a binary image, it is possible to always obtain a binary image optimal for characters at high speed regardless of the density of the characters of the document to be photographed.

The binary threshold setting circuit 216 calculates a binary threshold according to the density adjustment level set on the various setting mode screens (see FIG. 3), and the binarizer 217 sets the binary threshold. Since the image signal is binarized based on the binarization threshold set by the circuit 217 to generate a binary image,
It is possible to easily change the density level of the binary image.

Further, according to the present embodiment, when shooting in the character binarization mode, “4 images” is displayed in the “binary image display” of the various setting mode screens (see FIG. 3) in the character binarization mode. (Second mode) ”, the binarizer 217 generates a binary image with four different set densities, and displays the generated four binary images on the LCD 111. Therefore, by simultaneously displaying the four binary images binarized at the four set densities, the user can select an optimal binary image at a glance.

When four binary images are displayed on the LCD 111, a part of each binary image is displayed. Therefore, a part of the image is displayed without reducing the image. Accordingly, the quality of the binarized character can be accurately and easily determined.

Further, since the areas of the four binary images displayed on the LCD 111 can be changed by operating the keys 115 and 116, it is possible to easily display the part of the user's attention.

Further, one or a plurality of images from the four binary images displayed on the LCD
And the selected one or more binary images are recorded in the memory 219, so that the user can confirm the image and then save the image.

[0086] The present invention is not limited to the above-described embodiment, and can be implemented with appropriate changes within the scope of the present invention. For example, in the above-described embodiment, two (one and four) parameters of “binary image display” are set on the various setting mode screens (see FIG. 3) of the character binarization mode. The present invention is not limited to this, and the number of binary image displays may be two, eight, or sixteen. In addition, four parameters of "density adjustment" are set in the various setting mode screens (see FIG. 3) of the character binarization mode. However, the present invention is not limited to this. It may be more or less.

[0087]

As described above, according to the imaging apparatus of the first aspect, in the character photographing mode for photographing character information such as a document, the binarizing means is designated by the density designating means. Since the image signal is binarized to generate a binary image according to the density level of the binary image, the optimum binary image for characters can always be produced at high speed regardless of the density of the characters of the document to be photographed. It is possible to obtain.

According to the imaging apparatus of the second aspect, in the imaging apparatus of the first aspect, the binarizing means includes a binarizing means for converting the binary image according to the density level of the binary image designated by the density designating means. Since the binarization threshold at the time of binning is changed, it is possible to easily change the density level of the binary image in addition to the effect of the invention according to claim 1.

Further, according to the image pickup apparatus of the present invention, the image picked up in the character image pickup mode is converted into a binary image at a plurality of different set densities by the binarizing means.
Since the plurality of generated binary images are displayed on the display means, the user selects the most appropriate binary image at a glance by simultaneously displaying the binarized images at the plurality of set densities. It becomes possible.

According to the image pickup apparatus of the fourth aspect, in the first mode, the image picked up in the character photographing mode is binarized based on the density level of the binary image specified by the density specifying unit. In the second mode, an image captured in the character photographing mode is generated by the binarizing unit to generate a binary image at a plurality of different set densities, while the binary image binarized in is displayed on the display unit. Since the plurality of generated binary images are displayed on the display means, it is possible to always obtain an optimal binary image for characters regardless of the density of the characters of the document to be photographed, It is possible to select an optimal binary image at a glance.

According to the imaging device of the fifth aspect, in the imaging device of the third or fourth aspect, when displaying a plurality of binary images on the display means, a part of each binary image is displayed. Is displayed, so that in addition to the effect of the invention according to claim 3 or 4, the quality of the binarized character can be accurately and easily displayed by displaying a part of the image without reducing the size of the image. Can be determined.

[0092] According to the imaging apparatus of the sixth aspect, in the imaging apparatus of the fifth aspect, the operation means changes a partial area of each of the plurality of binary images displayed on the display means. Therefore, in addition to the effect of the invention according to claim 5, it is possible to easily display a portion of interest of the user.

According to the imaging apparatus of the present invention, in the imaging apparatus of any one of the third to sixth aspects, the selecting means may select one or a plurality of the binary images displayed on the display means. Is selected, and the selected one or more binary images are recorded in the recording means. In addition to the effect of the invention according to any one of claims 3 to 6, the user After confirming the image, the image can be saved.

Further, according to the character photographing method of the image pickup apparatus of the present invention, the density level of the binary image is designated, the subject light formed by the lens system is converted into an image signal, and the converted image is converted. Since the signal is binarized according to the designated density level of the binary image to generate a binary image, the optimum binary image for the text is always obtained regardless of the density of the text of the document to be photographed. It is possible to obtain.

Further, according to the character photographing method of the image pickup apparatus of the ninth aspect, the subject light formed by the lens system is converted into an image signal, and the converted image signal is converted to a plurality of different set densities. Generating a plurality of binary images, displaying the generated plurality of binary images on a display unit, selecting one or a plurality of images from the plurality of binary images displayed on the display unit, and selecting the selected one or a plurality of binary images. Since the value image is recorded in the recording means, the user can select and record the optimal binary image at a glance by simultaneously displaying the binarized images at a plurality of set densities. Become.

[Brief description of the drawings]

FIG. 1 is a top view showing a configuration of a digital camera according to an embodiment.

FIG. 2 is a rear view showing the configuration of the digital camera according to the embodiment.

FIG. 3 is a view showing various setting mode screens in a character binarization mode.

FIG. 4 is a diagram showing transition of switching of a density adjustment parameter.

FIG. 5 illustrates the L of a binary image captured in the character binary mode when the binary image display number parameter is set to four.
It is a figure showing the example of a display of CD.

FIG. 6 is a block diagram showing a configuration of a digital camera according to the present embodiment.

FIG. 7 is an explanatory diagram for describing automatic exposure control in a natural image mode.

FIG. 8 is an explanatory diagram for explaining automatic exposure control in a character mode and a character binarization mode.

9 is a diagram showing an example of a color filter array (checkerboard RGB filters) of the CCD shown in FIG. 6;

FIG. 10 is a block diagram showing a detailed configuration of the aperture corrector of FIG. 6;

FIG. 11 is an explanatory diagram for explaining coefficients of a Laplacian filter.

FIG. 12 is an explanatory diagram for describing an example of an image sampling cycle.

FIG. 13 is an explanatory diagram for describing an example of block division of an image.

FIG. 14 is a block diagram illustrating a detailed configuration of a non-low luminance pixel average value calculation circuit in FIG. 6;

FIG. 15 is a top view illustrating a configuration of a digital camera with a zoom lens.

FIG. 16 shows f = in the character mode and the character binarization mode.
It is a figure which shows the automatic exposure control program curve at the time of 56 mm.

FIG. 17: f = in character mode and character binarization mode
It is a figure which shows the automatic exposure control program curve at the time of 85 mm.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 digital camera 101 mode switching button 102 mode display unit 103 release 104 dial key 105 zoom switch 200 optical system 201 CCD 202 AGC circuit 203 A / D converter 204 white balance adjuster 205 luminance signal generation circuit 206 luminance signal generator 207 luminance Signal selector 208 Aperture corrector 209 Frame memory 210 Exposure control circuit 211 CPU 212 Comparator 213 Block buffer 214 Non-low luminance pixel average calculation circuit 215 Non-low luminance pixel detection threshold setting circuit 216 Binary threshold setting circuit 217 Binarization 218 Compressor 219 Memory 300 Vertical Laplacian filter 301 Horizontal Laplacian filter 302, 303 Absolute value circuit 304 Comparator 305 Selector 306 Adder 307 Comparison 308 parameter unit 400 the gate circuit 401 the adder 402 adds the result register 403 gate circuit 404 shift register 405 comparator 406 counter

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // H04N 9/07 H04N 1/40 103A 5C077 H04N 101: 00 5/91 J F-term (Reference) 5B029 AA02 BB02 DD05 5B047 AB02 BA10 DB05 DC13 5C022 AA13 AB03 AB12 AB13 AB17 AB20 AC03 AC13 AC42 AC56 AC69 CA07 5C053 FA08 FA27 GB12 JA16 KA04 KA24 KA25 LA01 LA04 LA06 LA11 LA14 5C065 AA07 BB00 CC01 CC03 DD02 GG02 GG02 GG02 GG02GG03 RR16 SS05 SS06 TT09

Claims (9)

[Claims] An image pickup apparatus having a character photographing mode for photographing character information such as a document, a lens system for forming an image of subject light, and an image pickup means for converting the formed subject light into an image signal A binarizing unit that binarizes the image signal to generate a binary image; and a density specifying unit that specifies a density level of the binary image when binarizing the image signal. An imaging device characterized in that: 2. The method according to claim 1, wherein the binarizing unit changes a binarizing threshold value for binarizing according to a density level of the binary image specified by the density specifying unit. 2. The imaging device according to 1. 3. An image pickup apparatus having a character photographing mode for photographing character information such as an original, a lens system for forming an image of subject light, and an image pickup means for converting the formed subject light into an image signal. And a binarizing unit for binarizing the image signal to generate a binary image; a display unit for displaying an image; and a recording unit for recording an image. An image pickup apparatus characterized in that a binary image is generated from the generated image at a plurality of different set densities by the binarizing unit, and the generated binary images are displayed on the display unit. 4. An image pickup apparatus having a character photographing mode for photographing character information such as a document, a lens system for forming an image of subject light, and an image pickup means for converting the formed subject light into an image signal. A binarizing unit that binarizes the image signal to generate a binary image; a density specifying unit that specifies a density level of the binary image when binarizing the image signal; Display means for displaying; and a recording means for recording an image, wherein the image captured in the character photographing mode is displayed on the basis of the density level of the binary image specified by the density specifying means. A first mode in which a binary image binarized by the binarizing unit is displayed on the display unit, and a binarized image obtained by the binarizing unit at a plurality of different set densities. Generate and generate Imaging device and having a second mode for displaying a plurality of binary image on the display means. 5. The imaging device according to claim 3, wherein when displaying the plurality of binary images on the display unit, a partial area in each of the binary images is displayed. . 6. The imaging apparatus according to claim 5, further comprising an operation unit for changing a partial area of each of the plurality of binary images displayed on the display unit. 7. The image processing apparatus according to claim 1, further comprising a selection unit that selects one or more images from the plurality of binary images displayed on the display unit, and records the selected one or more binary images on the recording unit. The imaging device according to any one of claims 3 to 6, wherein: 8. A character photographing method for an image pickup apparatus for photographing character information of a document or the like, wherein a step of designating a density level of a binary image and a step of converting subject light formed by the lens system into an image signal And a step of generating a binary image by binarizing the converted image signal according to a density level of the designated binary image. 9. A character photographing method for an image pickup apparatus for photographing character information of a document or the like, comprising: converting a subject light imaged by a lens system into an image signal; Generating binary images at respective set densities; displaying the plurality of generated binary images on a display unit; selecting one or a plurality of images from the plurality of binary images displayed on the display unit And a step of recording the selected one or more binary images in a recording unit.