JPH0414375A - Color picture reader - Google Patents

Abstract

PURPOSE:To prevent deterioration in the color reproducibility due to the dispersion in the reader or a secular change by executing automatically the calculation of a color conversion efficiency through the read of a test chart and storing the result in a storage means. CONSTITUTION:When a color conversion coefficient calculation mode is selected, a test chart 16 is read by a photodetector section 1 of a scanner 17. The information of the chart 16 read by the photodetector section 1 is pre-processed as required by a signal processing circuit 2 and stored in a memory circuit 3. A CPU 6 calculates a color conversion coefficient from a picture data of the chart 16 from the circuit 3 by using the arithmetic method. The calculated color conversion coefficient is at first stored in a storage circuit 7 by using the CPU 6. Then the scanner 17 sets the original to be read substantially and the photodetector section 1 reads the original and the signal processing circuit 2 applies prescribed picture processing to store the picture to the circuit 3. On the other hand, the color conversion coefficient stored in the circuit 7 is sent to a color conversion circuit 4 via the CPU 6 and the circuit 4 applies the color conversion to the picture data from the circuit 3 based on the color conversion coefficient from the circuit 7 and sends the result through the picture processing circuit 5.

Description

[Detailed Description of the Invention] [Industrial Field of Application] This invention relates to a color image reading device, and particularly to color image scanners applied to color facsimile machines, color copying machines, etc. The present invention relates to a color image reading device suitable for compensating for a decrease in color reproducibility.

[Prior art] Fig. 6 shows, for example, the document rNEC technical report Vol. 1.41 No. 3
1 is a block diagram of a conventional color image reading device disclosed in 1988J. In the figure, (18) is a CCD sensor equipped with a color filter for converting reflected light from a color document (not shown) into an electric signal according to the color. (19) is a CCD sensor that amplifies the electric signal from the CCD sensor (18). The drive amplifier (20) is the drive amplifier (19)
) is an A/D (analog/digital) converter that converts analog electrical signals into digital signals, (21) is a signal processing circuit that performs signal processing such as shading correction and noise reduction, and (22) is the obtained image. (23) is an image reduction circuit that reduces the size of the image in accordance with subsequent processing; (23) is an outline enhancement circuit that applies processing to emphasize the contours in order to improve the visual quality of the obtained image; (24) is an image A ring buffer circuit (25) operates in cooperation with a line memory circuit (29) arranged for vibrating line processing to speed up processing, and (25) is a table memory circuit (25).
8) is a color correction circuit that corrects the color signal according to a preset correction coefficient, and (26) is a binary correction circuit that performs error diffusion, etc. on the multi-valued image signal if necessary according to the requirements of the printer, etc. An error diffusion processing circuit that adds transformation processing, (
27) is a control circuit that controls a series of operations from processing the signal from the color original read by the CCD sensor (18) to sending it out from the error diffusion processing circuit (26).

The operation of the above configuration will now be described.

An analog image signal from a color original obtained from a CCD sensor (18) is amplified by a drive amplifier (19) and converted into digital multi-value information by an A/D converter (20). The signal processing circuit (21) removes noise from this image signal and converts it into a uniform signal with no distribution unevenness such as shading, and the image is reduced by the image reduction circuit (22) or contour enhancement circuit (23) according to post-processing requirements. Processing such as contour enhancement can be added. The color signal obtained here is corrected according to the color temperature of the light source when reading the original with the CCD sensor (18), color shift of the color filter, and color reproduction tendency of the printer or display device in the post-processing system. In order to achieve good color reproducibility, the color correction circuit (25) is connected through the ring buffer circuit (24).
) is given to In the color correction circuit (25), the table memory circuit (25) is preset according to the actual condition of each device.
A color correction calculation is performed based on the correction coefficients stored in 8), subjected to error diffusion processing through an error diffusion processing circuit (26), and sent as binary image information to an external printer or the like. Note that the ring buffer circuit (24) is arranged together with the line memory circuit (29) to perform continuous pipeline processing on continuously sent image signals, thereby enabling high-speed arithmetic processing.

Now, as mentioned above, the general tendency of such devices is that the light source, color separation filter, spectral sensitivity of the CCD sensor, color reproduction tendency of the output device such as printer or display, etc. are not necessarily in ideal conditions. There is no guarantee that you will be able to respond. Therefore, in order to ensure ideal color reproducibility, correction coefficients for color correction are stored in advance in the table memory circuit (28) according to the actual condition of each part, and the CCD sensor (18) is moved according to the correction coefficients. This means that the color correction circuit (25) applies color correction to the image signal taken in from the image signal.

Generally, the A/
The original signal digitally converted by the D converter (20) is converted into red (
The three primary colors of R), green (G), and blue (B) are RISGl and Bl, respectively.

On the other hand, if the color signals corrected by the color correction circuit (25) are three primary colors, RO, Gl, and Bl, respectively, color correction is performed based on the following equation.

Here, a, , (i-1 to 3, j-1 to 3) are correction J coefficients. This correction coefficient is calculated in advance and stored in the table memory circuit (28). Then, in the color correction circuit (25), a color correction calculation is executed by a hardware circuit based on the correction coefficients of the table memory circuit (28).

[Problems to be Solved by the Invention] Since the conventional color image reading device is configured as described above, it is possible to reproduce colors with good color reproduction while taking into account the differences in the characteristics of each part such as the light source, color separation filter, CCD sensor, display, and printer. It is necessary to store the optimal correction coefficient in advance in the table memory circuit (28) in order to link the same to the table memory circuit (28), but if the correction coefficient is applied in common to multiple devices, color reproduction may be affected due to variations in each device. It doesn't necessarily match. In addition, if the spectral characteristics of a light source or color separation filter are likely to change over time, table memory recovery (2
A major problem remains that color reproduction cannot be improved with the correction coefficient initially set in 8). On the other hand, it is possible to rewrite the contents of the table memory circuit (28) at any time according to the actual condition of the device.
Calculate the correction coefficient for each device and use the table memory circuit (2
Work such as rewriting 8) is almost impossible after the device is commercially available and used in various places. As mentioned above, conventional color image reading devices calculate color correction coefficients externally in advance and store them in table memory circuits, which makes it impossible to deal with variations in color reproducibility between individual devices, and color reproduction due to changes over time. There was an issue that needed to be resolved, namely the failure to respond to sexual deterioration.

This invention was made to solve the above-mentioned problems, and by adding color conversion processing within the device, it is possible to deal with variations in color reproducibility between individual devices and changes in color reproducibility due to changes over time. An object of the present invention is to obtain a color image reading device that can effectively improve this problem.

[Means for Solving the Problems] In order to solve the above problems, the present invention includes a photoelectric conversion means for converting an image on the document surface of a color original to be read into an electrical signal, and an output of the photoelectric conversion means. A color conversion means for performing conversion processing to obtain color information, a storage means for storing conversion coefficients of the conversion processing in the color conversion means, and a test chart in which a color chart containing at least one color-related information is arranged is stored in the photoelectric conversion means. The object of the present invention is to provide a color image reading device comprising a calculation means for reading a color image from a color image, calculating a conversion coefficient necessary for color conversion from the obtained read signal, and storing the conversion coefficient in the storage means.

[Operations] In the above means, the color image reading device of the present invention has the following features:
In photoelectric conversion, an image of the document surface of a color document to be read is converted into an electric signal, and in order to obtain color information by converting the output of the photoelectric conversion means in a color conversion means, in the calculation means, the color conversion means A test chart in which a color patch including at least one piece of information regarding color is arranged is read out from the photoelectric conversion means, a conversion coefficient necessary for color conversion processing is calculated from the obtained read signal, and the result is stored in the storage means. This results in better color reproducibility.

[Example〕 Hereinafter, the second invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram of a color image reading device according to an embodiment of the present invention. In the figure, (1) is a C with a color filter arranged to reflect light from the surface of a color document (not shown).
A light receiving section (2) is a signal processing circuit that performs processing such as shading correction and noise reduction on the image signal from the light receiving section (1); ) is a memory circuit that temporarily stores read image data, (4) is a color conversion circuit that performs color conversion of image data to improve the color reproducibility of image data, and (5) is a color conversion circuit that adjusts image quality. The image processing circuit (6) not only controls the entire device, but also calculates color conversion coefficients in the color conversion circuit (4) based on image data from the memory circuit (3) and stores them in the storage circuit (7). This is a CPU for keeping the computer running.

Next, the operation of the above configuration will be explained based on the flowchart in FIG. 2, the explanatory diagram of an example of the test chart in FIG. 3, and the explanatory diagram of the relationship between the scanner section and the test chart in FIG. 4. By the way, Figure 2 shows the CPU (6
) and the operation in actual image reading. Figure 3 is an example of a test chart used for calculating color conversion coefficients, and Figure 4 is an example of a color image reading device. It shows the relationship between the scanner (17) and the test chart (16) of FIG. 3.

Before powering on the apparatus, a test chart (16) is set in the scanner (17) in advance, as shown in FIG. As shown in FIG. 3, the test chart (16) is a color chart in which the brightness and saturation of a plurality of colors are continuously changed, and has n types of information. When the color conversion coefficient calculation mode is selected in the color conversion coefficient calculation step (8), the test chart reading step (9) is executed, and the test chart (16) is read by the light receiving section (1) of the scanner (17). It is done.

The information on the test chart (16) read by the light receiving unit (1) is subjected to necessary preprocessing in the signal processing circuit (2) and stored in the memory circuit (3) in the data storage step (10).CPU (6) ) extracts the image of the test chart (16) from the memory circuit (3) and calculates the color conversion coefficient in the color conversion coefficient calculation step (11) using a calculation method such as the multiple regression method. The color conversion coefficients are first stored in the storage circuit (7) from the CPU (6) in the color conversion coefficient storage step (12).
After the start step (13), which involves setting the original to be read in step 7) and instructing the original to be read, the image reading step (14) is entered, in which the light receiving section (1) reads the original and performs signal processing. A circuit (2) performs predetermined image processing, and the image is stored in a memory circuit (3).

On the other hand, the color conversion coefficients stored in the memory circuit (7) are stored in the CPU.
(6) to the color conversion circuit (4), which applies color conversion to the image data from the memory circuit (3) based on the color conversion coefficients from the memory circuit (7). , and is sent out through the image processing circuit (5). As a result, the color original is read based on the color conversion coefficient that optimizes the color reproduction of the test chart (16), so changes in color reproduction due to individual differences in devices and changes over time can be corrected. I can do it. Thereafter, the color original is read based on the color conversion coefficients stored in the memory circuit (7), so there is no need to read the test chart (16) every time the original is read.

Note that the calculation of the conversion coefficient to be stored in the memory circuit (7) is performed based on the reading of the test chart (16), or even if it is automatically performed when the device is powered on, it cannot be performed manually. The process may be performed on-demand, or may be performed at the time of factory shipment or during service maintenance. However, the memory circuit (7
), it is necessary to take measures such as providing power backup for the storage circuit (7) or using non-volatile memory.

In addition, in the above embodiment, a test chart having a plurality of color portions with different lightness and saturation was exemplified, but the implementation of the present invention is not necessarily limited to this, and extreme In this example, the color conversion coefficient may be set to obtain the optimal white balance and white level value using a single-color test chart, and the test chart can be selected as appropriate according to the characteristics of each part that affects color reproduction. It is something.

In the above embodiment, the color conversion coefficients stored in the memory circuit (7) are sent to the color conversion circuit (4) via the CPU (6), and the color conversion circuit (4) performs color conversion processing calculations. Although the configuration has been illustrated, as shown in FIG. 6, the memory circuit (7)
A look-up table (7a) is provided in place of , and data is written from the CPU (6) to the look-up table (7a) when calculating and storing color conversion coefficients, and color conversion calculations during actual document reading are performed. Color conversion circuit (
By configuring the process to be executed directly while referring to the lookup table (7a) in step 4), there is an advantage that the processing speed can be greatly improved.

C. Effects of the Invention As described above, according to the present invention, color conversion coefficients are automatically calculated through reading a test chart and stored in a storage means, thereby reducing the possibility of differences due to individual differences in devices or changes over time. This has the effect of preventing deterioration of color reproducibility and providing a color image reading device with excellent image quality and high reliability.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a color image reading device according to an embodiment of the present invention, FIG. 2 is a flowchart for explaining the operation of the configuration of FIG. 1, and FIG. 3 is an explanatory diagram showing an example of a test chart. , FIG. 4 is an explanatory diagram showing the relationship between the scanner unit and the test chart, FIG. 5 is a block diagram of a conventional color image reading device, and FIG. 6 is a block diagram of a color image reading device according to another embodiment of the present invention. It is a diagram. In the figure, (1) is a light receiving section, (2) is a signal processing circuit,
(3) is a memory circuit, (4) is a color conversion circuit, (5) is an image processing circuit, and (6) is a CPU. (7) is a memory circuit, (7a) is a lookup table,
(18) is a CCD sensor (19) is a drive amplifier, (
20) is an A/D converter, (21) is a signal processing circuit, (2
2) is an image reduction circuit, (23) is an edge enhancement circuit, and (24) is an image reduction circuit.
) is a ring buffer circuit, (25) is a color correction circuit, (2
6) is an error diffusion processing circuit, (27) is a control circuit, and (28) is a control circuit.
) is a table memory circuit, and (29) is a line memory circuit. In addition, in the figures, the same reference numerals indicate the same or equivalent parts. Agent: Patent Attorney Yoshi 1) Kenji (2 others) Explanatory diagram showing an example of a test chat Figure 3 Flowchart to explain the operation of the configuration shown in Figure 1 Figure 2 Explanation showing the relationship between the scanner section and the test chat Figure 4 4F17- 4F18-

Claims (1)

[Claims] A photoelectric conversion means for converting an image of the surface of a document to be read into an electrical signal, a color conversion means for processing the output of the photoelectric conversion means to obtain color information, and a storage means for storing conversion coefficients for processing in the color conversion means. and calculating means for causing the photoelectric conversion means to read a test chart in which a color chart containing at least one color-related information is arranged, and calculating a conversion coefficient to be stored in the storage means from the obtained read signal. Characteristic color image reading device.