JP3057800B2 - Color image reader - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image reading apparatus for converting a color image in a color facsimile or a color copying machine into an electric signal so as to reduce a difference in color reproducibility of each apparatus. is there.

[0002]

2. Description of the Related Art FIG. 6 shows NEC Technical Report Vol. 41 No. 3
1 is a circuit block diagram of a conventional color image reading apparatus shown in FIG.

In FIG. 6, reference numeral 24 denotes a CCD sensor,
25, an amplifier for amplifying the output of the CCD sensor 24; 26, an AD converter for A / D (analog / digital) conversion of the signal; 27, a signal processing unit for performing shading correction, noise reduction, etc .; Department,
29 is an edge enhancement unit, 30 is a ring buffer, 31 is a color correction unit, 32 is an error diffusion unit for binarizing an image, 3
Reference numeral 5 denotes a control unit for controlling the entire circuit, 34 denotes a table memory storing color correction coefficients, 33a to 33e denote line memories, and 36 denotes a D / A converter.

Next, the operation will be described. The image signal obtained from the CCD sensor 24 is amplified by an amplifier 25 and converted into a digital signal by an A / D converter 26. The image signal digitized by the A / D converter 26 is converted into a noise-free uniform signal by the signal processing unit 27.

Next, an image reducing section 28 and an outline enhancing section 29
The image signal that has entered the color correction unit 31 via the ring buffer 30 after the above image processing is subjected to a conversion process for improving the color reproducibility, and if binarization is required, error diffusion is performed. The data is binarized by the unit 32 and output.

Next, color correction will be described. A general tendency of color image reading devices is that, because the spectral distribution characteristics of a light source, a color separation filter, a CCD sensor, a display, a printer, etc. are not ideal, the color of image data once captured is corrected and color reproducibility is improved. Needs to be improved.

In general, red, green, and blue input signals that have been A / D converted are denoted by R1, G1, and B1, and color-corrected red, green, and blue signals are denoted by R1, G1, and B1, respectively.
Assuming that the green and blue output signals are R0, G0, and B0, the color correction is represented by the following equation (1).

(Equation 1)

In equation (1), a _ij (i = 1 to 3,
j = 1 to 3) are color correction coefficients. In general, the color correction coefficient shown in the equation (1) is calculated in advance, stored in the table memory 34 in FIG. 6, and the calculation of the equation (1) is performed by hardware.

However, the light source, color separation filter, C
Since the spectral distribution characteristics of a CD sensor, a display, a printer, and the like differ depending on each image reading device, the color reproducibility does not always match if a previously calculated color correction coefficient is used for a plurality of image reading devices. . Further, in the case of a multi-chip image sensor having a plurality of image sensor units, it is difficult to match the color reproducibility because each image sensor unit has a different spectral characteristic.

Further, since the spectral distribution characteristic is accompanied by aging, it is necessary to calculate an optimum color correction coefficient each time. However, in the circuit configuration shown in FIG. It is necessary to calculate the correction coefficient externally, and it is difficult to rewrite the correction coefficient in the table memory 34.

[0011]

The conventional color image reading apparatus is configured as described above, and the color correction coefficients are calculated outside the apparatus and stored in a memory in advance. There has been a problem that adjustment when color reproducibility is different cannot be performed, and that it is difficult to rewrite a correction coefficient on the way. In addition, when a plurality of image sensor units are provided, there is a problem that it is difficult to remove variations in individual characteristics.

Further, since the color correction coefficient is calculated using the least squares method assuming the simple linear transformation shown in the equation (1), the color reproducibility is not strictly defined in a color space other than the linear space. There was also a problem that good output results could not be obtained.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and can eliminate the difference in color reproducibility between individual color image reading apparatuses, and can prevent the spectral distribution characteristics from changing over time. It is an object of the present invention to obtain a color image reading device that can follow.

It is another object of the present invention to provide a color image reading apparatus which can further improve the color reproducibility of each color image reading apparatus and can automatically set an optimum color correction coefficient without relying on the subjectivity. And

[0015]

SUMMARY OF THE INVENTION A color image reading apparatus according to the present invention is provided with a color chart of one color which is long in the horizontal direction.
A multi-chip image sensor <br/> plurality of image sensors or Ranaru long arranged laterally to read the several colors arranged test chart, for a plurality of image sensors each disposed in the transverse direction Processing means for calculating color correction coefficients independently and storing the color correction coefficients in a storage means is provided.

Further, in the color image reading apparatus according to the present invention, a color chart of one color which is long in the horizontal direction is arranged in plural colors in the vertical direction.
A multi-chip image sensor of a plurality of image sensors or Ranaru long arranged laterally to read the test chart, a plurality of image sensors arranged in the lateral direction
Means for calculating independently the color correction coefficient for each, to have a width for each color charts of the test chart
The upper limit value and lower limit value of the ideal data are previously stored in the storage means.
Remember, the read data of each color chart is stored in the memory.
Within the range from the lower limit to the upper limit of ideal data
Or out of range, and if so, color
Means for evaluating the color reproducibility when the reproducibility is good and out of the range when the color reproducibility is poor, means for correcting the color correction coefficient by this evaluation and re-evaluating, and good color reproducibility by the above evaluation And a processing means for storing the color correction coefficient determined to be in the storage means.

[0017]

According to the present invention, a horizontally long color chip obtained by each of a plurality of image sensors arranged in a horizontal direction of a long multi-chip image sensor is vertically processed.
Color correction coefficients are independently calculated for the test chart data in which a plurality of colors are arranged in the direction, and stored in the storage unit. Therefore, each image sensor unit has an independent color correction coefficient, and there is no difference in color reproducibility between the image sensor units and no difference in color reproducibility between color image reading devices.

Further, according to the present invention, the test chip
Upper limit of ideal data with width for each color chart of chart
The value and the lower limit are stored in the storage means in advance, and the
Is the lower limit of the stored ideal data.
Check whether the value is within the range from the value to the upper limit or outside the range.
The color reproduction is good when it is within the range.
In some cases , each color correction coefficient calculated as having poor color reproducibility is evaluated. When the color reproducibility is evaluated as good, it is stored in the storage means as it is, and when the color reproducibility is evaluated as poor, When the color correction coefficient is corrected and the color reproducibility is evaluated to be good by the re-evaluation, it is stored in the storage unit. This correction of the color correction coefficient is repeated until the color reproducibility is evaluated to be good. As a result, a color correction coefficient with good color reproducibility can be obtained fully automatically in the color image reading apparatus.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a color image reading apparatus according to the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of one embodiment. In FIG. 1, 1
Is a document, 2 is a glass surface on which the document 1 is placed, 3 is a light source for illuminating the document 1, and 5 is a multi-chip image sensor having a plurality of image sensor units. The multi-chip image sensor 5, for example, JP-62- 293
No. 877 is used,
It is composed of independent (five) color image sensors. A correction circuit is provided for each color image sensor.

The output of the multi-chip color image sensor 5 becomes a serial sensor output in the order in which the filters are arranged. In each correction circuit, after the DC component is cut by a coupling capacitor, the output is amplified by two transistors.
The switch is switched by the output of the shift register in the section of each color timing of green and blue, a resistor is inserted into the emitters of the two transistors, the outputs of the two transistors are added to the differential amplifier, and the output is connected to the emitter resistance of the transistor. The output of the multi-chip color image sensor 5 corresponding to each color is made to correspond to the output of the differential amplifier by making it correspond to the ratio between the differential resistance and the collector resistance (load resistance).

That is, a color signal correction circuit for making the same for all the color image sensors which output the three color separated image signals in time series is provided, and the signal of each color of the output of each color image sensor is provided. This is for correcting variations. Here, returning to FIG. 1, reference numeral 4 denotes an image forming means such as a rod lens array for forming an image on the surface of the document 1 on the multi-chip image sensor 5.

The image of the original 1 formed by the multi-chip image sensor 5 is converted into an electric signal by the multi-chip image sensor 5, and an analog signal from the multi-chip image sensor 5 is converted to a head signal by the image forming means 4. After being input to the amplifier 6 and digitized and amplified there, the image signal from the head amplifier 6 is processed by the signal processor 7. The image data processed by the signal processing unit 7 is temporarily stored in the memory 8.

Reference numeral 9 denotes a color correction unit for improving the color reproducibility of image data, 10 an image processing unit for adjusting image quality, 11 a control of the entire color image reading apparatus, and calculation of a color correction coefficient. Central processing unit (CP)
U), 12 is a memory for temporarily storing image data, and 13 is a memory as color correction coefficient storage means for storing the calculated color correction coefficients.

The color correction coefficient storage means described in, for example, Japanese Patent Application Laid-Open No. 62-22060 is used, and optical image information obtained by optically scanning the image surface of the original 1 is stored in image units. In the case where sampling is performed and reading is performed, and image information of each read image is subjected to multi-value quantization and then r-corrected, r is corrected prior to reading of a document image.
In order to obtain a density reference signal at the time of correction, a density reference plate for optical scanning is provided with a plurality of reference planes having different densities. That is, the density reference plate is optically scanned, and data obtained by the line image sensor at that time is used as a density reference value when r-correcting multi-valued quantized digital image information of the original 1 to be subsequently read.

Next, the operation will be described. A test chart placed on a glass surface 2 as a document 1 is illuminated by a light source 3, and the reflected light is imaged on a multi-chip image sensor 5 by an imaging means 4, where it is photoelectrically converted and converted into an electric signal. Is done. The test chart data obtained from the multi-chip image sensor 5 is amplified and A / D-converted by the head amplifier unit 6, and the digital signal is temporarily stored in the memory 8 via the signal processing unit 7. The test chart data temporarily stored in the memory 8 is compressed by the CPU 11 and stored in the memory 12.

After the above operation is repeatedly performed for a plurality of color chips, a plurality of image sensors constituting the multi-chip image sensor 5 are formed on the CPU 11 based on the data of the compressed test chart in the memory 12. An optimum color correction coefficient corresponding to each of the units is calculated using a multiple regression method or the like, and stored in the memory 13. When reading an image, the previously calculated and stored color correction coefficients are transferred from the memory 13 to the color correction unit 9 via the CPU 11, and the image data from the plurality of image sensor units is transferred to each image sensor unit. Are independently corrected by the color correction coefficients described above, converted into image data having good color reproducibility, and output through the image processing unit 10.

FIG. 3 is a flowchart illustrating a sequence of a color image reading apparatus provided with a function of automatically calculating a color correction coefficient. Fig. 2 shows one color chart that is long in the horizontal direction and multiple colors in the vertical direction to calculate the color correction coefficient.
The test charts 21 arranged are shown. FIG. 4 shows a state where the test chart 21 is placed on a document of the image reading device 22.

In step S2, the data of the first color in FIG. 2 is read by the multi-chip image sensor 5 and stored in the memory 8 in FIG. 1, and the data in the memory 8 is compressed by the CPU 11 in step S3. 12 is stored. This series of reading operations is repeated for N colors, and after the CPU 11 determines that all the colors have been read in step S5, the process proceeds to step S6, where a color correction coefficient is calculated for each image sensor unit, and step S7 is performed.
Then, the CPU 11 stores the correction coefficient in the memory 13.

The above operation is automatically performed inside the color image reading apparatus. After storing the color correction coefficients in step S7, if the CPU 11 determines that the color correction coefficients of all the image sensor units have been calculated in step S8, the process proceeds to step S9, in which the processing routine of steps S2 to S7 is executed. The reading is started to perform the processing, and the processing routine of steps S2 to S7 is performed in step S10, and this processing routine can be executed a plurality of times.
A series of operations for automatically calculating the color correction coefficient in S7 can be executed again. Further, the data compression is a means for reducing the amount of data in order to store the data in the memory 8 in FIG. 1 in the memory 12, and an appropriate data compression method may be used as the method. Alternatively, a method of reducing the data amount by obtaining an average value in the image sensor may be adopted.

FIG. 5 is a block diagram showing the configuration of the second embodiment of the present invention. Reference numerals 1 to 1 in FIG.
The portion indicated by 3 is the same as that in FIG. In FIG. 5, data of the test chart temporarily stored in the memory 12 is subjected to arithmetic processing by the CPU 11, a color correction coefficient is calculated, and stored in the memory 13. When reading image data, the previously calculated and stored color correction coefficients are directly referred to the color correction unit 9 as a look-up table. As a result, the same effect as in the above embodiment can be obtained, and further, there is an advantage that the processing speed is improved because the CPU 11 is not interposed.

Next, a third embodiment of the present invention will be described. The configuration is the same as in FIG. FIG. 7 shows test charts 14 and 15 used for automatically generating a color correction coefficient and evaluating the color correction coefficient. Next, the operation will be described with reference to the flowchart of the sequence of the automatic correction of the color correction coefficient in FIG. Steps S1 to S10 are the same as in the first embodiment. In step S11, the color reproducibility of the color correction coefficient is evaluated. If it is determined that the color reproducibility is good, the color correction coefficient is directly stored in the memory 13 in step S7. If it is determined that the color reproducibility is not good, the color correction coefficient is corrected in step S12, and the process returns to step S11 to evaluate the color correction coefficient again. As a result, the correction of the color correction coefficient is repeated until it is determined that the color reproducibility of the color correction coefficient is good.

Here, the evaluation of the color correction coefficient will be described in detail. The calculated color correction coefficient is once stored in the memory 12. Then, based on the image data obtained by reading the portion for evaluating the color correction coefficient stored in the memory 12 and the calculated color correction coefficient, for example, a color correction expression such as the expression (1) is used. The color data after color correction is C
Calculate on PU11. Also, as shown in FIG. 9, ideal data having a width for each color chart of the test chart is prepared in the memory 12 in advance, and the upper and lower limits of the ideal data of each color are set. The difference between the R, G, and B values is determined. If the difference from the ideal data falls within a certain range, it is determined that the color reproducibility is good. If the difference does not fall within a certain range, it is determined that the color reproducibility is bad.

If the color reproducibility is poor, it is determined which data among R, G and B is far from the ideal data, the color correction coefficient is corrected correspondingly, and the color reproducibility is evaluated again. The correction of the color correction coefficient and the evaluation of the color reproducibility are repeated until it is determined that the color reproducibility is good.

FIG. 10 shows a fourth embodiment of the present invention.
The flowchart of the operation is shown. The configuration is the same as in FIG. Steps S1 to S11 are the same as those in the above embodiment. If it is determined in step S11 that the color reproducibility is not good, the color patch read data is corrected in step S13, and the process returns to step S6 to return to the color correction coefficient. Is calculated, and the color reproducibility can be corrected in the same manner as in the above embodiment.

[0035]

As described above, according to the present invention, the color correction coefficient is calculated independently for each image sensor section of the multi-chip image sensor and automatically in the color image reading apparatus. In addition, each image sensor unit has an independent color correction coefficient, there is no difference in color reproducibility between individual devices, and a highly reliable image quality can be obtained. Further, in the present invention, the color correction coefficient is corrected until the color reproducibility is improved, so that the color reproducibility can be further improved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a first embodiment of the device of the present invention.

FIG. 2 is a test chart for calculating a color correction coefficient according to the first embodiment of the present invention;

FIG. 3 is a flowchart for explaining the operation of the first embodiment of the present invention;

FIG. 4 is a perspective view of the device of the present invention in a test chart mounted state.

FIG. 5 is a configuration diagram of a device according to a second embodiment of the present invention.

FIG. 6 is a configuration diagram of a conventional device.

FIG. 7 is a test chart for calculating a color correction coefficient and calculating a color correction coefficient according to a third embodiment of the present invention;

FIG. 8 is a flowchart showing the operation of the device according to the third embodiment of the present invention.

FIG. 9 shows R, G, B according to a fourth embodiment of the apparatus of the present invention.
FIG. 8 is a diagram showing ideal data having a width of.

FIG. 10 is a flowchart showing the operation of the fourth embodiment of the present invention;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 document 3 light source 5 multi-chip image sensor 7 signal processing unit 8, 12, 13 memory 9 color correction unit 10 image processing unit 11 CPU 22 image reading device

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Masatoshi Kato 2-14-40 Ofuna, Kamakura City, Kanagawa Prefecture Mitsubishi Electric Corporation Living System Laboratory (56) References JP-A-63-117567 (JP, A) JP-A-62-101181 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04N 1/40-1/409

Claims (2)

(57) [Claims] A long multi-chip image sensor having a plurality of image sensors in a horizontal direction for illuminating a document surface, converting image light reflected from the document surface into an electric signal, and the multi-chip image sensor. Color correction means for performing color correction based on the output from the image sensor and outputting a signal, and storage means for recording a correction coefficient for performing correction by the color correction means;
To determine the color correction, one color chart that is long in the horizontal direction
The calculated color correction coefficient independently to the plurality of image sensors each of a plurality of colors arranged test chart based on the data read by the multi-chip image sensor in the vertical direction, the color correction coefficient in said storage means A color image reading apparatus comprising a processing unit for storing. 2. A long multi-chip image sensor having a plurality of image sensors in the horizontal direction for illuminating a document surface, converting image light reflected from the document surface into an electric signal, and the multi-chip image sensor. Color correction means for performing color correction based on the output from the image sensor and outputting a signal, and storage means for recording a correction coefficient for performing correction by the color correction means;
To determine the color correction, one color chart that is long in the horizontal direction
And means for calculating a color correction coefficient independently to the plurality of image sensors each of a plurality of colors arranged test chart based on the data read by the multi-chip image sensor in the vertical direction, each color chip of said test chart Width for
The upper limit value and the lower limit value of the ideal data having the
Means, and the read data of each color chart
From the lower limit to the upper limit of the stored ideal data
Check if it is within or outside of the range, and it is within the range
Color reproduction is good when it is out of range.
Means for evaluating the color reproducibility is bad, means for evaluation of color reproducibility is reevaluated to correct the color correction coefficient when poor, the color correction coefficient when the evaluation of color reproducibility became case or better Good A color image reading apparatus, comprising: a processing unit for storing the image data in the storage unit.