JPH10336386A - Image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce noise included in pixel data obtained through an optical sensor such as a line sensor. SOLUTION: When a stage is stopped (caption S11), a light emitting element is lighted and an R light is emitted to a film (caption S12). R pixel data by one line are read from a line sensor (caption S16). Then a G light is emitted onto the film (caption S17). G pixel data by two lines are read from the line sensor (captions S20, S23). Then a B light is emitted onto the film (caption S24) and B pixel data by one line are read from the line sensor (caption S28). G pixel data by two lines are averaged.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus which irradiates a color image recorded on a film with red, green and blue light, and reads the image using a line sensor.

[0002]

2. Description of the Related Art Conventionally, as an image reading apparatus of this type, a film to be read is intermittently transported along a direction orthogonal to the longitudinal direction of a line sensor, so that a red (R) and a green (G) are read. And blue (B) image data are read line by line. That is, the film is transported by a predetermined amount every time one line of pixel data is detected by the transport mechanism, and while stopped, the film is irradiated with R, G, and B light to emit R, G, and B image data. Is detected by the line sensor.

[0003]

The pixel data output from the line sensor includes noise generated during processing by the line sensor or an electric circuit connected to the line sensor. For this reason, there is a certain limit to the image quality of an image obtained based on this pixel data, and it has conventionally been desired to reduce this noise.

An object of the present invention is to provide an image reading apparatus capable of reducing noise contained in pixel data obtained through an optical sensor such as a line sensor.

[0005]

According to a first aspect of the present invention, there is provided a first image reading apparatus which receives light transmitted or reflected by a recording medium, thereby forming one line of pixel data corresponding to an image recorded on the recording medium. , An exposure control means capable of controlling exposure to the optical sensor and performing a plurality of exposures on the same line, and the one line output from the optical sensor a plurality of times by the plurality of exposures And pixel data processing means for outputting an average value or an intermediate value for each pixel.

When the image is a color image, the optical sensor outputs, for example, red (R), green (G) and blue (B) pixel data line by line. in this case,
It is preferable that the exposure control means can independently set the number of exposures for each of R, G, and B colors.

The exposure control means may be configured to set the number of exposures by operating display of the number of exposures formed on the screen of the display device.

The image reading apparatus may have a means for detecting the S / N ratio of one line of pixel data. In this case, the exposure control means increases the number of exposures as the S / N ratio decreases.

The number of exposures set by the exposure control means is, for example, a difference between the number of bits of a memory for storing pixel data of one pixel and the number of bits of pixel data of one pixel obtained by one exposure. It may be restricted.
In this case, when the number of bits of the memory for storing the pixel data of one pixel is BM and the number of bits of the pixel data of one pixel is BP, the number of exposures set by the exposure control means is 2 (BM- BP) power.

A second image reading apparatus according to the present invention is an image reading apparatus for reading an image recorded on a recording medium, comprising: an optical sensor for generating one line of pixel data by being exposed once; An exposure control means capable of setting the number of exposures for the same line, and a read control for reading out one line of pixel data from the optical sensor for each exposure when the exposure control means performs a plurality of exposures for the same line. Means.

A third image reading apparatus according to the present invention comprises a group of photoelectric conversion elements arranged along a predetermined direction, receives light transmitted or reflected by a recording medium, and corresponds to each photoelectric conversion element. A line sensor for generating pixel data,
Exposure control means for controlling exposure of the line sensor and reading of pixel data, movement means for relatively moving the line sensor and the recording medium in a direction orthogonal to the predetermined direction, and cooperation with the exposure control means and the movement means In a state where the relative position between the line sensor and the recording medium is kept constant, the exposure control unit performs the exposure and the reading operation of the pixel data a plurality of times, and the pixel data read out for each exposure is Pixel data processing means for generating an average value or an intermediate value of pixels.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an image reading apparatus according to one embodiment of the present invention.

A document M to be read used in this image reading apparatus is a transparent document (film), and a color image is recorded on the film. The document M to be read is intermittently transported in the direction of arrow A by the document transport mechanism 10. A light source 20 is provided above the passage of the original M to be read, and an image forming lens 31 and a line sensor 30 are provided below.
Is provided. The turning on and off of the light source 20 is controlled by a light source driving circuit 41, and the operation of detecting an image by the line sensor 30 is controlled by a line sensor driving circuit 42. The document transfer mechanism 10, the light source drive circuit 41 and the line sensor drive circuit 42 operate according to command signals output from the system control circuit 40.

The image data read from the line sensor 30 is amplified by an amplifier 43 and converted to a digital signal by an A / D converter 44. The digital image data is temporarily stored in the memory 46 after being subjected to shading correction in the image processing circuit 45. This image data is read from the memory 46 and subjected to predetermined arithmetic processing such as color correction and gamma correction. And the image data is
The signal is converted into a signal conforming to a predetermined format in the interface circuit 47 and output to a computer (image processing device) 60 via the input / output terminal 48. The image processing circuit 45 and the interface circuit 47 are controlled by the system control circuit 40.

In the present embodiment, all operations of the image reading apparatus are controlled by the computer 60. The switch 49 is connected to the system control circuit 40,
The operation of the image reading apparatus may be controlled by operating the switch 49.

FIG. 2 shows the document transfer mechanism 10, the light source 20, and the line sensor 30. The document M to be read is the frame 1
The frame 11 is fixed to a plate-like stage 12 by a stopper 13. The stage 12 has an opening (not shown) formed at a position corresponding to the document M to be read. Stage 12
A rack 14 is formed on a side end surface of the pinion 1. A pinion 1 provided on an output shaft of a document feed motor 15 is formed on the rack 14.
6 is engaged. The document feed motor 15 is driven under the control of the system control circuit 40, and the position of the document M to be read is controlled.

The light source 20 is located above the stage 12,
The light-emitting elements 21R, 21G, and 21B that emit blue (B), green (G), and red (R) light are periodically arranged in this order. Can be changed. Although only six light emitting elements are shown in FIG. 2, more or less light emitting elements may be provided. These light emitting elements 21R, 21G, and 21B are supported by an elongated support member 22 extending in the width direction of the stage 12, and a cylindrical lens 23 extending parallel to the support member 22 is provided between the support member 22 and the stage 12. ing. That is, the light emitted from the light emitting element 21 is condensed by the cylindrical lens 23 and is irradiated on the read original (film) M in a line shape.

The line sensor 30 is located below the light source 20 with the stage 12 interposed therebetween, and is provided in parallel with the light source 20 and the cylindrical lens 23. That is, the line sensor 30 extends in a direction substantially perpendicular to the direction in which the document M to be read is transported. An imaging lens 31 is provided between the line sensor 30 and the stage 12. Imaging lens 3
Reference numeral 1 extends in parallel with the line sensor 30 and is constituted by a rod lens array 32. Therefore, the read original M
When the light is irradiated by the light source 20, the image recorded on the read original M is formed on the light receiving surface of the line sensor 30 via the imaging lens 31.

FIG. 3 shows a configuration of the light source 20 and the line sensor 30 when a reflection original is used as the original M to be read. In this configuration, the light source 20 and the cylindrical lens 23 are disposed below the read original M together with the line sensor 30 and the imaging lens 31. That is, the light emitted from the light source 20 is applied to the lower surface of the original M to be read via the cylindrical lens 23, and the light reflected by the original M is imaged on the line sensor 30 via the imaging lens 31. .

FIG. 4 shows an example of a screen of a display device connected to the computer 60. The operation of the image reading apparatus according to the present embodiment is controlled by clicking a predetermined mark displayed on the screen of the display device using, for example, a mouse. That is, the information set via this screen is input to the system control circuit 40 via the input / output terminal 48 and the interface circuit 47, and various controls are performed.

For example, when the mark MP of "prescan" is clicked, prescan is executed. That is, the film M is scanned by the line sensor 30 at a relatively coarse pitch, and the image P obtained by this is scanned.
I is displayed on a part of the screen. On the other hand, when the “scan” mark MS is clicked, the main scan is executed, and the film M is scanned by the line sensor 30 at a relatively fine pitch. The image obtained by the main scan is displayed on, for example, the entire screen of the display device. On the other hand, when the “eject” mark ME is clicked, the film M is discharged from the image reading device.

Three boxes B1, B displayed under "exposure setting" on the screen of the display device
Numerical values indicating the number of exposures in reading R, G, and B images are set in 2 and B3, respectively. That is, in the present embodiment, when the pixel data of the same line of the same color component is read by the line sensor 30, a plurality of exposures are possible. For example, when 1, 2, and 1 are set in boxes B1, B2, and B3, respectively, exposure for R and B is performed once, but exposure for G is performed twice. The numerical values of these boxes B1, B2, B3 are input from, for example, a keyboard.

The number of exposures can be freely determined according to the user's preference in the manual mode, or can be automatically determined in the auto mode. That is, on the screen of the display device, when the white circle B4 formed beside "manual" is clicked and switched to a black circle, the number of exposures can be set in the manual mode. In this case, the number of exposures is displayed in boxes B1, B2, and B3. Exposure. On the other hand, when the white circle B5 formed next to "Auto" is clicked and switched to the black circle, an auto mode in which the number of exposures is automatically determined is set.

The other marks on the screen of the display device are not directly related to the present invention, and the description thereof will be omitted.

FIG. 5 is a timing chart showing an image reading operation when the number of exposures is set in the manual mode. In the example of this figure, the boxes B1, B2, and B3 on the screen of the display device each have 1,
2, 1 are set. That is, the number of exposures for R, G, and B is 1, 2, and 1, respectively.

With the stage 12 stopped (reference S1)
1) First, the light emitting element 21R is turned on, and the light of R is irradiated on the film M (reference S12). In this state, the shutter gate signal is switched from the off state to the on state (reference S13), and charge accumulation in the line sensor 30 is started. That is, the line sensor 30 generates one line of R pixel data. When the exposure time for R elapses, the readout gate signal is temporarily switched on (reference S14), and after the effective charge is transferred to the transfer path, the shutter gate signal is switched off (reference S15). . Next, one line of R pixel data is read from the line sensor 30 (reference S16).

During the reading of the R pixel data, the light emitting element 21R is turned off and the light emitting element 21G is turned on (reference S17). Then, similarly to the case of the R pixel data, the shutter gate signal is set to the ON state for a predetermined time (reference S18), and one line of G pixel data is generated in the line sensor 30. When the exposure time for G elapses, the readout gate signal is switched to the ON state (reference S19), and thereafter, one line of G pixel data is read from the line sensor 30 (reference S20).

When the reading is completed, the shutter gate signal is again set to the on state for a predetermined time (reference S21), and one line of G pixel data is generated in the line sensor 30. When the exposure time for G elapses, the readout gate signal is switched to the ON state (reference S22), and thereafter, one line of G pixel data is read from the line sensor 30 (reference S23). That is, the image data for one line of the G component at the same line position of the film M is read twice consecutively.

During the reading of the G pixel data, the light emitting element 21G is turned off and the light emitting element 21B is turned on (reference S24). Then, similarly to the case of the R and G pixel data, the shutter gate signal is set to the ON state for a predetermined time (reference S25), and the line sensor 30
, Pixel data of B for one line is generated. When the exposure time for B elapses, the readout gate signal is switched to the ON state (reference S26). After the effective charge is transferred to the transfer path, the stage 12 moves by two pulse signals and is set at the next reading position (reference S27).
Also, one line of B image data is read from the line sensor 30 (reference S28). During the reading of the B image data, the light emitting element 21B is turned off and the light emitting element 21R is turned on (reference S29).

As described above, with respect to one line of the image contained in the image recorded on the film M, R, G, and B pixel data are read out, and the read out pixel data is subjected to shading correction to the memory 46. Is stored in In the memory 46, R and B pixel data for one line are stored for each color component, but G pixel data is added to two lines and stored as one line data. That is, for G, two lines of pixel data are output for the same line image.

The average value of the G pixel data (Gn1 and Gn2) is obtained in the image processing circuit 45. In the image processing circuit 45, process processing such as color correction and gamma correction is performed on the R, G, and B pixel data of the n-th line that has just been read (reference S3).
1). During this process, the image data of the (n-1) th line for which the process has been completed is transferred to the computer 60 (reference S32).

When the transfer of the image data of the (n-1) th line is completed, the reading operation of the image data of the (n + 1) th line is started (reference S33). Such reading operation is performed for a predetermined number of lines (for example, about 1000 lines), and image data for one screen is stored in the computer 6.
Output for 0.

FIG. 6 is a flowchart showing the process executed in the image processing circuit 45.

In step 101, it is determined whether or not the number of exposures of R is one. If it is 2 or more, that is, if exposure is performed twice or more for R, step 10
In 2, each pixel data of R is divided by the number of exposures, and an average value thereof is obtained to be R pixel data. On the other hand, when the number of exposures of R is 1, the average value does not need to be obtained, and thus step 102 is skipped.

Similarly, in step 103, it is determined whether or not the number of exposures of G is one. If it is 2 or more, each pixel data of G is divided by the number of exposures in step 104, and an average value thereof is obtained to be G pixel data. When the number of exposures of G is 1, step 104 is skipped. In step 105, the number of exposures of B is 1
Is determined. If the number is equal to or greater than 2, in step 106, each pixel data of B is divided by the number of exposures, and an average value thereof is obtained, and is set as pixel data of B.
When the number of exposures of B is 1, step 106 is skipped.

As described above, by performing exposure a plurality of times for a predetermined color component of R, G, and B and taking an average value, noise included in pixel data of the color component is reduced. It should be noted that the noise reduction effect can be obtained even if the average value is not calculated as described above, but an intermediate value of data obtained by a plurality of exposures is obtained.

In step 107, filter processing having a correlation with adjacent pixels is performed on the R, G, and B pixel data.
This is a process for preventing an extreme difference from occurring between each pixel and an adjacent pixel, and is executed to further remove noise. However, if the noise has been sufficiently reduced by a plurality of exposures as described above, the processing of step 107 may be omitted.

In step 108, color balance adjustment (white balance adjustment) is performed on the R, G, and B pixel data.
Is performed. In step 109, gamma correction is performed on the R, G, and B pixel data subjected to the color balance adjustment, and the program ends.

As described above, in the image reading apparatus of the present embodiment, the line sensor 30 is exposed a plurality of times in the detection of an image of a predetermined color component by the user's selection, and the pixel data of a plurality of lines obtained by this is obtained. Can be adopted as pixel data of the color component. Therefore, noise included in the pixel data of the color component can be reduced, and the image quality of the reproduced image can be improved.

As described above, the number of exposures of the line sensor 30 can be set in the auto mode as described below.

FIGS. 7 and 8 are flowcharts showing a program for setting the number of exposures in the auto mode. In this program, only one line at a specific position (for example, the center of the screen) of the image recorded on the film M is detected by the line sensor 30. In this program, the line sensor 30 is 1024
It is assumed that there are two photodiodes. Note that P
x [n] is data of a predetermined pixel in any one of R, G, and B color components, x indicates the number of exposures,
n indicates the position of the pixel on the line sensor.

In step 201, exposure is performed once. In step 202, pixel data P1 [0] to P1 generated in the line sensor 30 by the exposure in step 201
1 [1023] is stored in the memory 46.

In step 203, the line sensor 30 is exposed, and the pixel data obtained by the exposure is stored in the memory 4.
Exposure / storage operation of storing the data in the memory 6 is performed twice. In step 204, two lines of pixel data generated in the line sensor 30 by the two exposures are read from the memory 46, and an average value is obtained for each pixel.
The data is stored in the memory 46 as one line of pixel data P2 [0] to P2 [1023]. That is, for example, the pixel data P2 [0] is an average value of the 0th two pixel data.

In step 205, the sum of squares K ₂₁ of the difference between the pixel data P2 [n] obtained by two exposures and the pixel data P1 [n] obtained by one exposure is calculated. Pixel data P2 [n] and pixel data P1
The difference from [n] decreases as the noise included in the pixel data decreases. That is, the sum K ₂₁ is smaller as the noise included in the pixel data is smaller, that is, the S / S
As the N ratio increases, the value approaches zero. In step 206,
Sum K ₂₁ is greater or not than the first reference value. When the sum K ₂₁ is equal to or less than a first reference value, that is, when the S / N ratio of the pixel data is large, required is determined not to perform multiple exposure. Therefore, in this case, the number of exposures is set to 1 in step 207, and this program ends.

On the other hand, if it is determined in step 206 that the sum K ₂₁ is larger than the first reference value, steps 211 and the subsequent steps are executed to perform exposure a plurality of times. In step 211, four exposure / storage operations are performed. In step 212, the average value of the pixel data stored in the memory 46 is obtained by the four exposure / storage operations, and the average value is stored in the memory 46 as pixel data P4 [0] to P4 [1023].

In step 213, the sum K of squares of the difference between the pixel data P4 [n] obtained by the four exposure and storage operations and the pixel data P2 [n] obtained by the two exposure and storage operations is calculated. ₄₂ is calculated. In step 214, whether the sum K ₄₂ is greater than the second reference value. When the sum K ₄₂ is smaller than the second reference value, the number of exposure is judged sufficient by two. Therefore, in this case, the number of exposures is set to 2 in step 215, and this program ends.

On the other hand, when it is determined in step 214 that the sum K ₄₂ is larger than the second reference value, in step 221 the exposure and storing operation is performed eight times. In step 222, the average value of the pixel data stored in the memory 46 is obtained by the eight exposure / storage operations, and is stored in the memory 46 as pixel data P8 [0] to P8 [1023].

[0048] At step 223, the sum K ₈₄ of the squares of the difference between the pixel data P4 [n] obtained by the exposure of eight pixel data P8 obtained by exposure of [n] and 4 times is calculated. In step 224, it is determined whether the sum _K84 is greater than a third reference value. Sum _K84 is the third
Is less than or equal to the reference value, it is determined that the number of exposures is four. Therefore, in this case, the number of exposures is set to 4 in step 225, and this program ends.

On the other hand, if it is determined in step 224 that the sum K ₈₄ is larger than the third reference value, the number of exposures is set to 8 in step 226, and the program ends.

In the flowcharts of FIGS. 7 and 8, the magnitudes of the first to third reference values are determined according to the purpose, and may be different values or may be all the same value.

Next, the limitation on the number of exposures will be described. Pixel data obtained by a plurality of exposures is stored in a memory 46.
, And is subjected to arithmetic processing to obtain an average value. Therefore, in the memory 46, if the number of bits for storing the data of one pixel is relatively small, an overflow may occur if the value of the addition result of the pixel data is too large. This limits the number of exposures. That is, the number of times of exposure is determined by the difference between the number of bits of the memory for storing the pixel data of one pixel and the number of bits of the pixel data of one pixel obtained by one exposure, and stores the pixel data of one pixel. The number of bits of the memory for this is BM, and the number of bits of the pixel data of one pixel is BP.
The number of exposures that can be set is 2 to the power of (BM-BP). For example, when the number of bits of the memory for storing the pixel data of one pixel is 16 and the number of bits of the pixel data of one pixel is 10, the number of exposures that can be set is ²⁶ .

[0052]

As described above, according to the present invention, noise included in pixel data obtained via an optical sensor such as a line sensor can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an image reading apparatus according to an embodiment of the present invention.

FIG. 2 is a perspective view showing a document transport mechanism, a light source, and a line sensor when a transparent document is used as a document to be read.

FIG. 3 is a diagram illustrating an arrangement of a light source, a line sensor, and the like when a reflective original is used as the original to be read;

FIG. 4 is a diagram illustrating an example of a screen of a display device connected to a computer.

FIG. 5 is a timing chart showing an image reading operation when the number of exposures is set in a manual mode.

FIG. 6 is a flowchart illustrating a process performed in the image processing circuit.

FIG. 7 is a flowchart showing the first half of a program for setting the number of exposures in the auto mode.

FIG. 8 is a flowchart showing a latter half of a program for setting the number of exposures in the auto mode.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Document transfer mechanism 20 Light source 30 Line sensor M film

Claims (9)

[Claims] An optical sensor for generating one line of pixel data corresponding to an image recorded on the recording medium by receiving light transmitted or reflected by the recording medium;
Exposure control means capable of controlling exposure to the optical sensor and performing multiple exposures on the same line, and pixel data of the one line output multiple times from the optical sensor by the multiple exposures, An image reading apparatus comprising: pixel data processing means for outputting an average value or an intermediate value for each pixel. 2. The image processing apparatus according to claim 1, wherein the image is a color image, and the optical sensor outputs pixel data of red (R), green (G), and blue (B) line by line. Image reading device. 3. The image reading apparatus according to claim 2, wherein said exposure control means can set the number of exposures independently for each of R, G, and B colors. 4. The image according to claim 1, wherein the exposure control means is configured to set the number of exposures by operating a display of the number of exposures formed on a screen of a display device. Reader. 5. An apparatus according to claim 1, further comprising: means for detecting an S / N ratio of the one line of pixel data, wherein the exposure control means comprises:
2. The image reading apparatus according to claim 1, wherein the smaller the ratio, the greater the number of exposures. 6. The number of exposures set by the exposure control means is defined by the number of bits of a memory for storing pixel data of one pixel and the number of bits of pixel data of one pixel obtained by one exposure. The image reading device according to claim 1, wherein the image reading device is limited by a difference. 7. When the number of bits of a memory for storing pixel data of one pixel is BM and the number of bits of pixel data of one pixel is BP, the number of exposures set by the exposure control means is 7. The image reading apparatus according to claim 6, wherein the power is 2 (BM-BP). 8. An image reading apparatus for reading an image recorded on a recording medium, wherein an optical sensor that generates one line of pixel data by being exposed once and a number of times of exposure for the same line can be set. A plurality of exposure control means, and a read control means for reading out the pixel data of the one line from the optical sensor each time the exposure is performed a plurality of times on the same line by the exposure control means. Characteristic image reading device. 9. A line sensor comprising a group of photoelectric conversion elements arranged along a predetermined direction, receiving light transmitted or reflected by a recording medium, and generating pixel data corresponding to each photoelectric conversion element; Exposure control means for controlling exposure to a line sensor and reading of pixel data; movement means for relatively moving the line sensor and the recording medium in a direction orthogonal to the predetermined direction; exposure control means and the movement means In cooperation with the relative position between the line sensor and the recording medium being kept constant, the exposure control means executes the exposure and pixel data read operations a plurality of times, and is read out for each exposure. An image reading apparatus comprising: pixel data processing means for generating an average value or an intermediate value of each pixel for pixel data.