JPH0479474A - Color picture reader - Google Patents

Abstract

PURPOSE:To calculate the optimum color correction coefficient even when secular change is generated in a reading means and the properties of a color chip by calculating the color correction coefficient from the value reading plural color chips and the target value of the specified color correction stored in a color correction target value storage means. CONSTITUTION:The reference value of a scanner reading data against plural color chips used by a color correction coefficient calculation mode is stored in a reference data storage means 16, and plural color chips 14 are read by a color picture reading means 1, and the obtained digital color picture data is compared with the data against the corresponding color chip stored in the reference data storage means 16. The color correction coefficient is calculated from the digital color picture data obtained by reading plural color chips in a color correction coefficient calculation means 8 and the color correction target value corresponding to the comparison result obtained by a comparison means 17 to be stored in a color correction coefficient storage means 5. Thus, the optimum color correction can be performed even when the secular change is generated in integral spectroscopic sensitivity characteristics and in the spectral reflectance characteristics.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a color image reading device, and particularly to a color image reading device that takes a color document and generates digital color pixel data, and further processes the digital color pixel data. The present invention relates to a color image reading device having a function of performing color correction on images.

[Prior Art] Conventionally, among color image reading devices that have a function of reading a color document, generating digital color pixel data, and further performing color correction on the digital color pixel data, a color image reading device that reads a plurality of color patches is used. A color image reading device is known that has a color correction coefficient calculation mode that calculates a color correction coefficient based on read data, and performs color correction using the calculated color correction coefficient.

FIG. 2 is a block diagram showing an example of the structure of a conventional color image reading device. 9 is a color original, 1 is a color image reading means, 2 is a digital processing means, 3 is a selector, 4 is a color correction calculation means, 5 is a color correction coefficient storage means,
6 is a color image display device; 7 is a color correction target value storage means;
8B is a color correction coefficient calculation means.

FIG. 3 is a side view showing an example of the configuration of the reading means 1 of the color image reading apparatus described in item 1. A color original 9 on a document table 10 made of glass or the like is illuminated by an illumination light source 11, and the reflected light passes through a lens 12 and forms an image on a color image sensor 13.

A color filter is provided on each reading pixel of the color image sensor 13, and color separation is performed. The color-separated image is input to each reading pixel, and a signal corresponding to the intensity of light is output.

A color image sensor configured as described above normally performs color separation on three separated colors. As for color separation, R (red) and G (
(green) and B (blue), and in that case, the color separation system is often composed of color filters of the above-mentioned separated colors, but it can also be composed of color filters of complementary colors. Based on the spectral characteristics of the color filter, illumination light source, image sensor, and lens mentioned above, the color image reading means as a whole has the spectral sensitivity characteristics shown by the solid line in FIG. 4, for example, with respect to wavelengths in the visible region. The spectral sensitivity characteristics of the color image reading means as a whole will be referred to herein as the overall spectral sensitivity characteristics. When a color original is read using such a system, the spectral reflectance 'I) of the color original and
A color image signal is output based on the relationship with the overall spectral sensitivity characteristics of the color image reading means.

The reading unit comprising the illumination light source, lens, and color image sensor is scanned in the direction of the arrow by a scanning mechanism (not shown) in FIG. 3, and the entire surface or a portion of the color document is read.

In FIG. 2, the color image signal generated by reading the color original 9 by the color original & converted to data.

If you try to display the image directly on a CRT or output it to a color printer using the above digital color pixel data, it may not be suitable for color originals due to distortions in the spectral sensitivity characteristics of the color image reading means 1, differences in color system, etc. Color reproduction cannot be obtained.

For this reason, color correction processing is usually performed on digital color pixel data. In order to simplify the explanation below,
The output of a color image will be explained using an additive color image display device such as a CRT.

As a means of color correction, a color correction matrix is prepared and the color correction matrix is applied to digital color pixel data to perform color correction.
A look-up table reference method is known in which the relationship between input and output for color correction processing is prepared in advance in a look-up table, and color correction is performed each time the look-up table is referenced for digital color pixel data. It is being Here, it is assumed that the former color correction 7-trix calculation method is used as the color correction method.

In FIG. 2, digital color pixel data is subjected to color correction processing by color correction calculation means 4 using color correction coefficients stored in color correction coefficient storage means 5. The color correction calculation performed by the color correction calculation means 4 is mainly for correcting distortions in the spectral sensitivity characteristics of the color image reading means 1 mentioned in 1. - Digital color pixel data written in R (red), G (green), B
(blue), for example, the simplest 3
When using 7x3 trixes, color correction processing is performed using the following equation.

The obtained digital color pixel data, R', GB' is the digital color pixel data after color correction obtained by the color correction calculation means 4, and A-(a+, +) is the color correction matrix used by the color correction calculation means 4. It is.

Note that although the simplest 3×3 matrix has been described here, a higher-order matrix may also be used.

The digital color pixel data subjected to color correction processing by the color correction calculation means 4 is displayed on a color image display device 6 such as a CRT.
will be displayed.

Next, a method of calculating the color correction 7 trix in the color correction coefficient calculation mode will be explained. First, the selector 3 is switched to b, and a plurality of color marks 14, which are fixed to a part of the document table 10'2 at a position where they can be read by the color image reading means 1 and provided under the protective cover 15, are colored. An image reading means 1 reads the image, and a digital processing means 2 obtains digital color pixel data. Obtained multiple color charts 1
A set of digital data (R, G, B) for each of the plurality of color patches 14 and a set of color correction target values for each of the plurality of color patches 14 (R8Go,
From the set Bo), (R, G, B) becomes (Ro, G.

Bo) is calculated using the method of least squares or the like.

As the plurality of color patches used at this time, it is desirable to use a large number of color patches in which the colors of the document are distributed as evenly as possible within the uniform color space.

In the color correction coefficient calculation mode, instead of the color chart fixed on the document table 9, a sheet-like one that can read the document table]0 in the same way as a normal color document may be used.

The color correction coefficient calculation mode as described above does not need to be performed every time a color document is read, but may be performed at appropriate time intervals. In other words, the overall spectral sensitivity characteristics of the color image reading means may change over time.
For example, in a color image reading means using a color separation system using color filters, the spectral transmittance characteristics of the color filters change depending on the usage environment such as temperature, humidity, and ultraviolet rays. Along with this, a part of the overall spectral sensitivity characteristic of the color image reading means shifts from, for example, Ga shown by the solid line in FIG. 4 to Gb shown by the broken line.

The color correction coefficients calculated for the initial overall spectral sensitivity characteristics of the color image reading means are initially optimal and provide sufficient color correction, but due to changes in the spectral transmittance characteristics of the color filters as described above. After the overall spectral sensitivity characteristic of the color image reading means is shifted, the initial color correction coefficient is no longer optimal. If color correction processing is performed in such a state using color correction coefficients for the initial state, good color reproduction will not be obtained because the color correction coefficients are not optimal.

Therefore, by using the color correction coefficient calculation mode to calculate color correction coefficients as appropriate and performing color correction processing using the calculated color correction coefficients, the decline in color reproducibility due to changes in overall spectral sensitivity characteristics over time can be avoided. It becomes possible to prevent it.

[Problem to be solved by the invention]

As mentioned above, even in a color image reading device that has a plurality of color patches and calculates color correction coefficients based on the data read from them as appropriate, each of the plurality of color patches used in the calculation of the color correction coefficients changes over time. There is a problem in that color fading occurs and the spectral reflectance characteristics change. In other words, as shown in FIG. 5, for a color chart that has spectral reflectance characteristics as shown by the solid line in the initial state,
After a period of time, a change occurs as shown by the broken line. Therefore, even if an attempt is made to calculate a color correction coefficient based on data obtained by reading a color patch that has changed due to oral changes, the target value corresponding to each of a plurality of color patches is 1-1. .

[Means for Solving the Problems] In order to solve these problems, the present invention reads a color original, generates digital color pixel data, and performs color correction processing on the digital color pixel data described in 1. In a color image reading device having a color correction calculation means and a color correction record+lV means for storing color correction coefficients used in the color correction calculation means, a plurality of color chips used for calculating the color correction coefficients used in the color correction processing are stored. a reference data storage means for storing corresponding reference digital color pixel data; digital color pixel data corresponding to the plurality of color charts recorded in iQ in the digital color pixel data storage means; a comparison means for comparing digital color pixel data obtained by actually reading the color chart; a color correction target value recorder 11 means for storing a color correction target value corresponding to the comparison result in the comparison means; The color correction coefficient calculating means calculates a color correction coefficient from the values obtained by reading a plurality of color charts and the color correction target value stored in the color correction target value storage means.

[Effect]

By doing the above, even if the overall spectral sensitivity characteristics of the color image reading means and the spectral reflectance characteristics of the color chart change over time, it is possible to always calculate the optimal color correction coefficient for the color reproduction system. can.

〔Example〕

An embodiment of the present invention will be described below based on the drawings.

FIG. 1 is a block diagram showing an example of the configuration of a color image reading apparatus according to the present invention. 16 is a reference data storage means, and 17 is a comparison means. ”-Standard data record・1. The a means 1G stores reference values of scanner read data for a plurality of color patches used in the color correction coefficient calculation mode. The reference value may be, for example, scanner read data of the L color chart in its initial state. Further, the color correction target value storage means 7 stores color correction target values with respect to elapsed time for a plurality of color chips used in the color correction coefficient calculation mode. The color correction target value for the above-mentioned elapsed time is determined by performing preliminary environmental tests and the like on each of a plurality of color chips.

First, a procedure for calculating a color correction coefficient in the color correction coefficient calculation mode will be described. First, the selector 3 shown in FIG. 2 is switched to b, and as shown in FIG. Step 2 obtains digital color pixel data. The obtained digital color pixel data is stored in the comparison means 17 as reference data notation means]
6 was memorized. Compare data for corresponding color patches. For example, if scanner read data for the color chart in the initial state is given as reference data, the difference in data obtained by comparison will correspond to the elapsed time. At this time, it is not necessary to use RGB for all the plurality of color charts.
It is not necessary to compare all data. For example, even for separated colors where the change over time in the overall spectral sensitivity characteristic can be ignored, data for a color chart whose spectral reflectance characteristics change over time so that the change in signal value is the largest, or conversely, for the overall spectral sensitivity In contrast to separated colors whose sensitivity characteristics change significantly over time, there is a color chart in which there is almost no change in spectral reflectance characteristics over time, and when reading the separated colors whose sensitivity characteristics change significantly over time, the difference in value appears to some extent large. It is sufficient to compare only the data for.

Specifically, in the cases of FIGS. 4 and 5, examples include a B signal for reading the 8fr JJ of the blue color patch, or a G signal for reading the yellow color patch. The color correction target value storage means 7 stores color correction target values corresponding to the comparison results.

Next, the digital color pixel deck obtained by reading a plurality of color patches in the color correction coefficient calculation means 8 and the comparison means 1
From the color correction target value corresponding to the comparison result obtained in step 7,
Color correction coefficients are calculated by the method of least squares or the like. The calculated color correction coefficient is stored in the color correction coefficient storage means 5.

Next, a case will be described in which an arbitrary color original is read and outputted to a color image display device. First, the selector 3 is switched to a, and an arbitrary color original is read by the color image reading means 1. The color correction calculation means 4 performs a color correction calculation using the color correction coefficients which have been set to 1 or 0 in the color correction coefficient storage means 5. Thereafter, the color image display device 6B outputs the image.

In the above explanation, we have described the case where color correction processing is performed by performing matrix calculations based on color correction coefficients, but it is also possible to create a color correction lookup table and refer to it as described above. It is also possible to perform color correction by

Furthermore, in the above explanation, it is stated that the read digital color pixel data is immediately outputted by the color image output means, but it is also possible to temporarily store the digital color pixel data in the computer's memory, or to output it externally to the computer. The information described in 4.1 may be stored in the storage device, or image processing may be performed as necessary.

〔Effect of the invention〕

As described above, according to the present invention, in color correction processing for digital color pixel data generated by reading a color document with a color image reading device, the overall spectral sensitivity characteristics and color chart of the color image reading means are calculated. Even if the spectral reflectance characteristics of the sensor change over time, it is now possible to always perform optimal color correction on the read digital color pixel data.

[Brief explanation of the drawing]

FIG. 1 is a configuration block diagram showing the configuration of a color image reading device according to the present invention, FIG. 2 is a configuration block diagram showing an example of the configuration of a conventional color image reading device, and FIG. 3 is a configuration block diagram of the color image reading means 1. FIG. 4 is an explanatory diagram showing an example of the overall spectral sensitivity characteristics of the color image reading means, and FIG. 5 is an explanatory diagram showing an example of the spectral reflectance characteristics for a plurality of color chips. 4...Color correction calculation means 5...Color correction coefficient record (9 means 7...Color correction target value storage means 8...Color correction coefficient calculation means 16...Reference data record 10 Means 17...・Applicant for comparative means or more Seiko Electronic Industries Co., Ltd. Patent attorney Keinosuke Hayashi

Claims (1)

[Scope of Claims] Color correction calculation means for reading a color original to generate digital color pixel data and performing color correction processing on the digital color pixel data, and storing color correction coefficients used by the color correction calculation means. In a color image reading device having a color correction coefficient storage means, the reference data storage stores reference digital color pixel data corresponding to a plurality of color charts used for calculating the color correction coefficients used in the color correction process. means for comparing digital color pixel data corresponding to the plurality of color patches stored in the reference data storage means and digital color pixel data obtained by actually reading the plurality of color patches; a color correction target value storage means for storing a color correction target value corresponding to a comparison result of the color correction target value storage means; and a color correction target value stored in the color correction target value storage means and the value obtained by reading the plurality of color charts. A color image reading device comprising: color correction coefficient calculation means for calculating a color correction coefficient from a value.