JPH0580863B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical field to which the invention pertains] This invention relates to a device that converts a color image into an electrical signal using one or more image sensors and outputs the image to a color display device using this electrical signal. It relates to something that can provide stable image output even when the image is damaged. [Technical background of the invention and its problems] Conventionally, when converting a color image into an electrical signal using an image sensor and outputting it to a color printer, etc., there is a drawback that the color tone of the output image changes when the light source changes. Ta. In particular, since there are large changes immediately after the light source is turned on, it has not been possible to deal with subtle color changes just by stabilizing the light source. Further, when reading using a plurality of sensors, there is a drawback that due to differences in the characteristics of each sensor, subtle color changes occur in a band-like manner in the output image, making it very unsightly. [Object of the Invention] The present invention has been made to eliminate the above-mentioned drawbacks. Even if the light source etc. is unstable, a standard black and white pattern is input every time scanning is started, and this data is used to determine the standard of each sensor. The purpose of the present invention is to provide a device that corrects variations between sensors and outputs stable images. [Summary of the Invention] In the present invention, a color image is converted into an electrical signal using one or more color image sensors. At this time, just before starting one page scanning, a standard black and white pattern is scanned, and data for standardizing the output signal of each image sensor is calculated using this data and recorded in the memory. Based on this data, the output signal of each image sensor after scanning is standardized. Next, this standardized signal is converted by a matrix circuit. At this time, the coefficients of the matrix circuit are switched for each color image sensor so that almost the same signal is obtained no matter which color image sensor performs photoelectric conversion. At this time, if there is a color change within the color image sensor, the coefficients of the matrix circuit are switched for each pixel. The coefficients of the matrix circuit are corrected using a standard color pattern common to color image sensors. [Effects of the Invention] In the present invention, a standard black and white pattern is scanned immediately before starting scanning, and a signal for standardizing each sensor output is created. Therefore, if the light source is stabilized so that the amount of light is approximately constant for only a short period of time during one page scanning period, a stable signal that is not affected by aging of the light source can be obtained. Further, the coefficients of the matrix circuit are changed for each image sensor or pixel so that the signal is almost the same regardless of which image sensor performs photoelectric conversion. This means that the color filters of each sensor are corrected, so a stable signal can be obtained even when the hue changes due to differences in the light emission temperature of the light source. [Embodiment of the Invention] An embodiment of the present invention will be described below with reference to the drawings. First, the signal flow will be explained, and then the generation of standard signals for standardization will be explained. Figure 1 shows how the self-cleaning lens 1 cleans an original using four space-divided color filters.
This is an embodiment in which an image is formed on an image pickup device consisting of a CCD line sensor 3, photoelectrically converted, and this signal is used to send an electric signal to a color printer 29 for color display. The output electrical signal of the CCD line sensor 3 (for example, shown in Lecture No. 1243 "High-speed color close-contact scanner" (Hosaka et al.) at the 1981 Institute of Electronics and Communication Engineers National Conference) is amplified by the amplifier 4.
The AD converter 5 converts it into a digital signal.
This signal is divided into three colors, for example, white, yellow, and cyan, corresponding to each color filter, and stored in line memories 6, 7, and 8, respectively. 3
~5 operate in the same way for each CCD element 3, 3', 3''3, and line memory 6, 7,
8 and output as one line signal. Here, it is desirable that the resolution of the image formed by the self-occurring lens be about 1/2 of the resolution of the CCD line sensor. Now, the signals of one line for each color are averaged every two pixels by the next register 9 and adder 10. In other words, one pixel is recorded in register 9, and at the next point, the next data is added to register 9, and the output of the adder is connected.
Shift 1 bit to the MSB side. In this way, two-pixel averaging is performed to eliminate aliasing noise due to sampling. Next, normalization is performed on the signals for each pixel of each sensor to correct shedding. Now, when the white level signal of the standard test pattern is I _W and the black level signal is I _B , and if the output of this 1-line signal is I, then the standardized output signal I _O is as follows: . I _O = (I - I _W )・1/(I _B - I _W ) ...(1) To perform this for each pixel, I _W is recorded in advance in the line memory 11, and the adder 10 The output signals from the subtracters 12 and 12
Subtraction is performed pixel by pixel. Then I/(I _B −
The value of I _W ) is recorded in the line memory 13 in advance, and the multiplier 14 sequentially multiplies it pixel by pixel. The same process is performed for other color signals as well. By performing such processing, even if shading occurs in the CCD sensor, an output signal with almost no unevenness in brightness can be obtained. However, if there is a change in the characteristics of the color filter, it may be output as a subtle color change. Therefore, the next step was to use a matrix circuit consisting of a product-sum calculation circuit to be able to respond to subtle color changes between each image sensor, and to reduce the memory capacity of the color conversion table. Coordinates are transformed so that they are uniformly distributed in the memory address space of the color conversion table. Furthermore, here,
I used a color conversion table that performs nonlinear conversion, but
This memory does not necessarily need to be used when high-precision color reproduction is not required. As a color filter on the CCD sensor,
The three colors are white, yellow, and cyan, and the output signals from these are W, Y, and C, respectively. Furthermore, the luminance signal is S ₁ , the first color difference signal is S ₂ , and the second color difference signal is S ₃ , and each is defined as in the following equation. Note that the brightness signal may be S ₁ =W. S ₁ =Y+C-W S ₂ =W-Y S ₃ =W-C (2) Next, coordinate transformation is performed using the following equation. If the converted coordinates are respectively X ₁ , X ₂ , and X ₃ , then the following equation is obtained. _{X 1 X 2 _ _ _ _ _ _ _ _ _ _ _} The distribution is determined to be uniform. for example,
Make it equidistant from each color of yellow, cyan, and magenta. At this time, the matrix aij in equation (3) is determined by measuring S ₁ , S ₂ , and S ₃ for each color, and
The coordinates X ₁ , X ₂ , and X ₃ after conversion are determined for the values. Then, aij can be determined by calculating the inverse matrix from these values. Therefore, even if S ₁ , S ₂ , and S ₃ for each color are different for each sensor, it is possible to make the coordinates X ₁ , X ₂ , and X ₃ the same after conversion, and the aij can be found. Therefore, the following equation can be obtained from (2) and (3). _{X 1 X 2 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _} -a ₃₂ a ₃₁ -a ₃₃ W Y C ... (4) The signal flow for the conversion formula determined in this way is as follows. That is, each of the standardized W, Y, and C signals is selected by the multiplexer 15,
For each, the coefficient of equation (4) is calculated by the sum-of-products calculation circuit 16.
By multiplying by and adding, X ₁ , X ₂ , and X ₃ can be found.
At this time, if the coefficients of equation (4) are obtained in advance for each image sensor and recorded in the memory 17, and the coefficients are switched and calculated for each image sensor, variations between the elements can be eliminated. Note that in a CCD sensor, there may be variations in each pixel, and in this case, by switching coefficients for each pixel, it is possible to suppress variations in hue for each pixel. Also, the coefficients aij
If this is determined, the memory capacity required for the color conversion table can be small. Now, the signals coordinate-transformed in this way are then subjected to averaging processing, and the color conversion table is drawn using the averaged signals.The local fluctuation rate of the luminance signal is determined by a predetermined value for the values of this table. Only when the value is larger than the value, binarization is performed using a fixed threshold, and in other cases, dithering is performed. This will be explained with reference to FIG. The signals after coordinate transformation output from the product-sum calculation circuits 16, 16', 16'' are sent to the averaging processing circuits 18, 1.
8' and 18''.Next, for the luminance signal, the subtracter 19 takes the difference between the averaged signal and the original signal.As a result, this signal is the same as the luminance signal. gives local fluctuations.Furthermore, this signal has 2
The value is input to the value dither judgment memory 20. The contents of this memory are as shown in Table 1, for example.

【table】

Claims (1)

[Claims] 1. A color input/output device that converts a color image into an electrical signal using a color image sensor using a color filter under the same light source, and outputs a color image from a color printer using the converted electrical signal. In the apparatus, in order to correct the shading of the color image sensor, the color image sensor is standardized using a common reference pattern, and the electrical signals obtained by the standardized color image sensor are converted into brightness by a matrix circuit. When converting into signals and color difference signals, the coefficients of the matrix circuit are switched for each color image sensor or each pixel, and the coefficients corrected using a standard color pattern common to the color image sensors are used as the coefficients of the matrix circuit. A color input/output device characterized in that it is used.