JPH05344332A - Picture processor - Google Patents

Abstract

PURPOSE:To output a satisfactory neutral grey signal and a satisfactory coloring signal to the entire density area of an original. CONSTITUTION:A shading correcting circuit 34 repeatedly operates a shading correction based on an output gain obtained by reading a white shading board 17, and controls the output gain so as to be constant. In the state, the shading correcting circuit 34 operates the shading correction to a picture signal obtained by reading the original, and a luminance correcting circuit 35 operates a luminance correction based on the picture signal obtained by the shading correcting circuit 34.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus, for example, an image processing apparatus applicable to a device such as a color scanner.

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand for development of a color scanner with the colorization of the printing industry. Such a color scanner is equipped with a white shading correction plate, which performs so-called shading correction for correcting non-uniformity of the optical system and output non-uniformity of individual pixels of the image sensor for reproduction. It is general to take a method of eliminating image unevenness. At the same time, the reference colors of all the colors expressed by the color separation of the reading system are the colors of the shading correction plate.

[0003]

As described above, the color scanner corrects the nonuniformity of the optical system by the shading correction process, but the white plate (shading plate) is used.
Since the standard color is used as the reference color, the white area of the original is completely corrected, but the neutral gray area of low density area to high density area is not reproduced as gray when the image is reproduced on a color printer. It may be reproduced in color. An example of this state is shown in FIG. In FIG.
The abscissa represents the numerical value of the neutral gray density, and the ordinate represents the read value (data is white for 255, 0 for data).
Is black). As can be seen in FIG. 2, the white area of the document (point A in the figure) has the same RGB value (255),
It is reproduced in white, but as the gray density increases, RG
It can be seen that the balance of B is lost and the signal is not neutral gray.

As a cause of such a phenomenon, it is considered that the RGB image signal outputs of the color image sensor are non-uniform in balance, and the linearity of the analog circuit varies. Needless to say, such a problem is a problem of a general color copying machine. In particular, in the case of color facsimile, the method of transmitting and receiving the brightness data read by the scanner is generally used, so the sending side (scanner)
Since it is impossible to match the receiving side (printer) with the receiving side (printer), that is, it is not possible to know what kind of characteristics the other side has, the scanner or the printer, so data correction is not performed sufficiently and various colors are displayed. The problem of being reproduced occurs.

The present invention has been made in view of the above-mentioned drawbacks of the conventional example, and an object of the present invention is to minimize the unevenness of scanning due to variations in scanner, that is, variations in illumination optical system. The point is to provide an image processing device that can do so. Further, in recent years, development demands for color scanners and color printers have been increased along with colorization in the printing industry. Since a bubble jet printer (hereinafter abbreviated as "BJ printer") has appeared as a color printer, the printer configuration is simple and the running cost is relatively low. An example of such a BJ printer is shown in FIG. In FIG. 12, a BJ head (print head) 21 has a structure in which 128 nozzles are arranged in a line. When the BJ head 21 is moved in the direction of the arrow while printing is performed, a band-shaped image is printed by one movement of the BJ head. Not to mention the color scanner to which such a BJ printer is connected, the band scan type scanner is most suitable. That is, as shown in FIG. 13, a scanner that reads a band-shaped image with one movement of the reading unit 13 by moving the reading unit 13 including the 128-pixel line sensor 51 in the direction of the arrow while reading the image. Is.

With the color printer and the color scanner having the above-mentioned configuration, the read image can be processed in real time and printed out. If the scanner unit scans by a method other than band scanning, it is necessary to store all the images that have been read in memory once and convert them into a band-shaped or line-shaped data array suitable for the printer without printing them. Don't However, this method requires an enormous memory capacity for accumulating image data, and also consumes a great amount of time before printing out.

In the color scanner as described above,
A white shading correction plate is provided. This shading correction plate is generally used to correct unevenness of the optical system and output unevenness of individual pixels of the image sensor, that is, so-called shading correction to eliminate unevenness of a reproduced image. .. In the case of the band scanner type scanner, the shading correction plate 17
14, is placed near the home position 41 on the platen glass 11, that is, near the reading start position, and the shading correction plate is read just before the reading is started to perform the shading correction. In FIG. 14, 42
Is an index attached to the platen glass 11. The arrow in the drawing indicates the reading movement direction of the reading unit 13.

However, as described above, the color scanner corrects the nonuniformity of the optical system by the shading correction process. However, if the shading waveform before correction has extremely unevenness, the correction is sufficiently performed. There are times when I can't forget. That is, even if the shading waveform is such that shading correction can be sufficiently performed in the case of simple grayscale reading such as in a black and white scanner, R, G, and B are respectively used in the case of performing color separation of R, G, and B. If insufficient correction occurs in the pixels of, even if the signals of the individual pixels are uneven within the allowable range, the colors expressed by combining the three colors may be uneven. Especially, in the low density region, unevenness may occur. It tends to stand out. Possible causes of undercorrection include non-uniformity of linearity of the analog circuit in the reading unit and quantization error when converting the analog image signal into a digital image signal.

Among them, since the line width of the one-dimensional color line sensor using the band scan type color scanner is as short as about 10 mm, a point light source is generally used as an illumination light source. For this reason, it is difficult to illuminate the original with a uniform light amount or a uniform spectral distribution due to the state of the reflecting mirror provided in the reading unit, the diffraction phenomenon by the edge portion of the member, and the like. Therefore, shading unevenness becomes relatively large.

FIG. 16 shows a graph of the read data before shading correction with respect to the pixel address of the conventional color image sensor 51 by point light illumination. A schematic diagram of the point light source optical system is shown in FIG. Figure 1
In FIG. 9, 110 is a point light source, 12 is a self-focusing lens array (hereinafter abbreviated as SLA), and 51 is a color image sensor. As can be seen from FIG. 16, RGB
It can be seen that each pixel has a separate shading waveform. Further, FIG. 17 shows a graph of read data with respect to pixel addresses when a light gray original is read after shading correction.

According to FIG. 17, the shading correction is satisfactorily performed in the central part of the pixel address, but the end part of the address is colored instead of neutral gray because of insufficient correction, that is, You can see that it is uneven. Therefore, another object of the present invention is to use a line light source as a light source of a band-scan type color scanner to illuminate a document with a uniform light amount, and then perform shading correction, so that the end portion of an address is also corrected. An object of the present invention is to provide an image processing device capable of excellent shading correction.

[0012]

[Means for Solving the Problems]
In order to achieve the object, an image processing apparatus according to the present invention provides a first correction unit that performs shading correction based on an output gain obtained by reading a predetermined irradiation target, and an image signal obtained by reading an original. A second correction unit that performs shading correction and a brightness correction unit that performs brightness correction based on the image signal obtained by the second correction unit are provided.

[0013]

According to this structure, the first correction means performs shading correction based on the output gain obtained by reading the predetermined object to be irradiated, and the second correction means obtains the image signal obtained by reading the original. The shading correction is performed, and the brightness correction means performs the brightness correction based on the image signal obtained by the second correction means.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. <First Embodiment> FIG. 3 is a block diagram showing the arrangement of a color scanner according to the first embodiment of the present invention. In the figure, 31 is a color image sensor, 32 is an analog amplifier, 33 is an A / D converter, 34 is a shading correction circuit, 35 is a brightness correction circuit, 36 is a CPU for controlling the whole, and 37 is for the CPU 36 to operate. ROM storing programs, 38 is R storing various programs
AM.

FIG. 4 is a diagram showing positions where shading correction is performed in the color scanner according to the first embodiment. Figure 4
, 41 is a document, 42 is a reading unit, 43
Is a shading plate, 44 is a light source, 45 is a Selfoc lens array (hereinafter abbreviated as “SLA”), and 46 is a document table. Next, the flow of signal processing when reading with a color scanner will be described.

In FIG. 4, the scanner moves the reading unit 42 to the position shown in the figure and performs shading correction as a preprocessing before starting reading the original 41. The shading plate 43 has a standard white density of a color scanner. As shown in FIG. 4, the scanner illuminates the shading plate 43 illuminated by the light source 44, and the SL
Reading is performed by the color image sensor 31 via A45. The color image sensor 31 has 128 picture elements (12
8 × 3 pixels) photo sensor, and R,
Color filters are vapor-deposited in a dot-sequential manner, such as G, B, R, G, B, ... SLA 45 is the manuscript table 4
The image of the surface of No. 6 is set on the color image sensor 31 in the same size. As shown in FIG. 3, the analog image signal output from the color image sensor 31 is amplified by the analog amplifier 32 and input to the A / D converter 33. The A / D converter 33 converts into an 8-bit digital image signal according to the level of the input analog signal. The output of the A / D converter 33 is input to the shading correction circuit 34, and the shading correction is performed under the control of the CPU 36.

Here, the shading correction will be briefly described. FIG. 8 is a flow chart for explaining the shading correction operation according to the first embodiment. The shading correction according to the present embodiment is performed by the color image sensor 31.
However, the shading plate 43 is read (step S
1), store in memory (step S2). Using this shading data, the gain when the image data of any one pixel output from the A / D converter 43 outputs 255 is set to 1, and the gain is increased as it becomes smaller than 255 (gain = 255 / shading The plate read data) is corrected so that the read output of the shading plate 43 after the shading correction is uniform, that is, 255 (step S3). By performing the sensitivity unevenness correction of the pixels of the color image sensor 51 as described above, the reading unevenness of the scanner is eliminated.

When the shading correction described above is completed, the scanner starts reading the original. The color image signal output from the color image sensor 31 is similar to the shading correction sequence in the analog amplifier 3
2. The shading correction circuit 34 performs shading correction via the A / D converter 33. The output of the shading correction circuit 34 is brightness-corrected by the brightness correction circuit 35.

Next, the brightness correction circuit 35 will be described. After the shading correction described above is completed, the operator causes the scanner to read an achromatic gray chart in which the density step changes uniformly from black to white. The density step of the gray chart has a density of 17 steps from pure black to pure white.

FIG. 5 shows the output value of the scanner when this gray chart is read. The horizontal axis represents a numerical value of gray density, where 0 is black and 255 is white. The vertical axis represents the read data. As can be seen from FIG. 5, the G signal has a linear characteristic with respect to the gray density, but the R signal and the B signal are not linear as compared with the G signal. In order for the brightness correction circuit 35 to perform good gray reproduction in the entire density range, for example, in the direction of the arrow in FIG. 1, the characteristics of the R signal shown in FIG. The data may be shifted and converted into the characteristics shown by the solid line. As a method, general table conversion using a RAM or the like is sufficient.

The table for the characteristics of FIG. 5 can be easily realized by calculating the gain for the input value (0 to 255) for each of the RGB signals. FIG. 6 is a diagram showing the gain with respect to the input value. FIG. 7 shows the state of the output value of the brightness correction circuit 35 described above. You can see how the neutral gray is reproduced for all density ranges.

As described above, it is generally well known that when the neutral gray is reproduced in the entire density range, the color reproducibility of colors other than gray, that is, the color is improved. The output data of the brightness correction circuit 35 is sent to an external device and processed such as data storage and image reproduction.

As described above, according to the first embodiment, for the brightness data after shading correction, a brightness correction table is created based on the read values of a plurality of gray charts, and the brightness correction is performed. By doing so, it is possible to output a good neutral gray signal and a good color signal for the entire density range of the document. <Second Embodiment> FIG. 10 is a block diagram showing the arrangement of a color scanner according to the second embodiment of the present invention. In the figure, 51 is a color image sensor, 52 is an analog amplifier, 53 is an A / D converter, 54 is a shading correction circuit, and 55 is an image processing circuit.

FIG. 9 is a schematic diagram showing an optical system of a color scanner according to the second embodiment. In the figure, 11 is a linear white light source and 12 is an SLA. First, the flow of signal processing when reading with a color scanner will be described with reference to FIGS. 10 and 11. FIG. 11 is a diagram showing positions where the color scanner performs shading correction in the second embodiment.

In FIG. 11, as a natural process before starting the reading of the original 12, the scanner moves the reading unit 13 to the position shown in the figure and performs shading correction. The shading plate 17 has a standard white density of a color scanner. As shown in FIG. 11, the scanner illuminates the shading plate 17 illuminated by the light source 16 with S
Reading is performed by the color image sensor 51 via the LA 12. The color image sensor 51 has 128 picture elements (12
8 × 3 pixels) photo sensor, and R,
Color filters are vapor-deposited in a dot-sequential manner, such as G, B, R, G, B, ... SLA 12 is the manuscript table 1
It is set so as to form an image of the surface of No. 1 on the color image sensor 51 at the same size. As shown in FIG. 10, the analog image signal output from the color image sensor 51 is amplified by the analog amplifier 52 and input to the A / D converter 53. The A / D converter 53 converts into an 8-bit digital image signal according to the level of the input analog signal. The output of the A / D converter 53 is input to the shading correction circuit 54, and the CPU (not shown)
Shading correction is performed under the control of.

Here, the shading correction will be briefly described. Shading correction is performed when the color image sensor 51 reads the shading plate 17
When the image data of any one pixel output from the / D converter 53 outputs 255, the gain is set to 1 and 255
The smaller the value, the greater the gain (gain =
(255 / shading plate read data), the reading output of the shading plate 17 after shading correction is corrected to be uniform, that is, 255. By performing such sensitivity unevenness correction of the pixels of the color image sensor 51, the reading unevenness of the scanner is eliminated. The above operation is the same as that of the flow chart described with reference to FIG. 8 in the first embodiment.

FIG. 15 is a graph showing the read data of the shading plate 17 before (a) shading correction and after (b) shading correction with respect to the pixel address of the color image sensor 51 in the second embodiment. For comparison with FIG. 17, FIG. 18 shows a graph of read data with respect to pixel addresses when a light gray original is read after shading correction.

When the shading correction described above is completed, the scanner starts reading the original. The color image signal output from the color image sensor 51 is similar to the shading correction sequence in the analog amplifier 5
2. The shading correction circuit 54 performs shading correction via the A / D converter 53. The output of the shading correction circuit 54 is subjected to image processing such as edge enhancement and γ conversion by the image processing circuit 55. This image data is sent to a color BJ printer (not shown), and the read image is printed and reproduced.

As described above, according to the second embodiment, the line light source is used as the light source of the band scan type color scanner, and the shading correction is performed almost completely, thereby eliminating the uneven reading. can do. The present invention may be applied to a system including a plurality of devices or an apparatus including a single device. Further, it goes without saying that the present invention can be applied to the case where it is achieved by supplying a program to a system or an apparatus.

[0030]

As described above, according to the present invention,
It is possible to minimize uneven reading due to variations in the illumination optical system.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a state of correction accuracy according to a first embodiment.

FIG. 2 is a diagram illustrating a state of an output signal of a color sensor for neutral gray.

FIG. 3 is a block diagram showing a configuration of a color scanner according to the first embodiment.

FIG. 4 is a diagram illustrating positions where shading correction is performed in the color scanner according to the first embodiment.

FIG. 5 is a diagram showing output values of a color sensor for a predetermined gray chart in the first embodiment.

FIG. 6 is a diagram showing a gain with respect to an input value.

FIG. 7 is a diagram showing a state of output values of a brightness correction circuit 35.

FIG. 8 is a flowchart illustrating a shading correction operation according to the first embodiment.

FIG. 9 is a schematic diagram showing an optical system of a color scanner according to a second embodiment.

FIG. 10 is a block diagram showing a configuration of a color scanner according to a second embodiment of the present invention.

FIG. 11 is a diagram showing a position where the color scanner performs shading correction in the second embodiment.

FIG. 12 is a diagram illustrating an example of a BJ printer.

FIG. 13 is a diagram showing how a document is read.

FIG. 14 is a diagram showing a state of a platen glass.

FIG. 15 is a graph showing read data of the shading plate 17 before (a) shading correction and after (b) shading correction for pixel addresses of the color image sensor 51 in the second embodiment.

FIG. 16 is a graph showing the read data before shading correction with respect to the pixel address of the color image sensor 51 by point light illumination in the related art.

FIG. 17 is a graph showing read data with respect to pixel addresses when a light gray original is read after shading correction in the related art.

FIG. 18 is a graph showing read data with respect to pixel addresses when a light gray original is read after shading correction in the second embodiment.

FIG. 19 is a schematic view of a conventional point light source optical system.

[Explanation of symbols]

 11 line light source 12 SLA 13 reading unit 17 shading plate 21 BJ head 31 color image sensor 32 analog amplifier 33 A / D converter 34 shading correction circuit 35 brightness correction circuit 41 original 42 reading unit 43 shading plate 44 light source 45 SLA 46 original glass table 41 Home Position 42 Index 51 Color Image Sensor 52 Analog Amplifier 53 A / D Converter 54 Shading Correction Circuit 55 Image Processing Circuit 110 Point Light Source

Claims (6)

[Claims] 1. A first correction means for performing shading correction based on an output gain obtained by reading a predetermined object to be irradiated, and a second correction means for performing shading correction of an image signal obtained by reading an original. An image processing apparatus comprising: a brightness correction unit that performs brightness correction based on an image signal obtained by the second correction unit. 2. The image processing apparatus according to claim 1, wherein the first and second correction means are the same shading correction circuit. 3. A reading unit for reading a predetermined object to be illuminated with a white light source, a first correcting unit for performing shading correction based on an output gain obtained by the reading unit, and an image signal obtained by reading an original document. An image processing apparatus comprising: a second correction unit that performs shading correction. 4. The image processing apparatus according to claim 3, wherein the first and second correction means are the same shading correction circuit. 5. The image processing apparatus according to claim 3, wherein the white light source is a line light source. 6. The image processing apparatus according to claim 3, wherein the image processing apparatus uses a band scan method.