JPH04290376A - Picture reader - Google Patents

Abstract

PURPOSE:To obtain a high-resolution line sensor overshadowing color slurring. CONSTITUTION:Signals obtained from the two-lined line sensor, being divided into R and B signals on the first line and B and G signals on the second line, are respectively subjected to sample-and-hold. The B signal which is subjected to sample-and-hold in the both first and second lines is added with 1/2 weighting by an adder circuit 6. The first and second-line B filters are arranged on the same phase.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading device, and more particularly to a color image reading device that separates one pixel into a plurality of color signals and reads the signals. For example, it is applied to color scanners.

0002

2. Description of the Related Art Publicly known documents describing the prior art related to the present invention include, for example, a "color original reading device" proposed in Japanese Patent Laid-Open Publication No. 173962/1982. The device in this publication is designed so that the arrangement density of the color stripes on the color stripe filter varies depending on the color, thereby achieving miniaturization. Also, JP-A-2-113
There is a "color signal separation circuit for image sensor" proposed in Japanese Patent No. 765. In this publication, light-receiving element rows are arranged in two rows, red and blue filters are arranged alternately in the first row, and white light-receiving elements are arranged in the second row. As described above, in conventional color reading devices with filters directly attached, the light receiving element is configured using a color point sequential method in which the three colors R, G, and B are sequentially arranged in the filters forming one pixel, as shown in FIG. was. In this case, the resolution of the reading device is only 1/3 that of a black and white reading device because one pixel is represented by three light receiving elements on the sensor. Furthermore, as shown in FIG. 6, there is a three-row configuration in which the three colors R, G, and B are each provided with separate light-receiving element rows. However, in this case, the sensor configuration becomes larger and a buffer for three lines is required to read the three colors in the same way in the sub-scanning direction. Therefore, we have adopted a filter array as shown in Figures 7 and 8, in which the number of G filters among R, G, and B is increased and other filters are decreased, or a two-row configuration as shown in Figure 9, with one row (white). ) A configuration has also been proposed in which filters of one color, green, and two colors, red and blue, are arranged alternately. However, although these methods have a high pixel density, the colors of adjacent pixels of the imported pixels are 1/2 cycle out of phase between red and blue, and color shift between red and blue is likely to occur. . Additionally, since pixels are captured at green resolution, there is a drawback that color shift is easily noticeable at high resolution.

0003

[Object] The present invention was made in view of the above-mentioned circumstances, and an object of the present invention is to provide an image reading device having a high-resolution line sensor in which color shift is less noticeable.

0004

[Structure] In order to achieve the above objects, the present invention provides (1)
It consists of a color separation filter of a plurality of different colors, a color light receiving element arranged so that one filter of the color separation filter covers one light receiving surface, and a line image sensor constituted by the light receiving element, In a color image reading device having a filter configuration in which the plurality of color separation filters have different arrangement densities of color filters depending on the color, the plurality of color separation filters include color separation filters of three colors, and the three colors of the color separation filters. A first line sensor in which light receiving elements are arranged alternately in the main scanning direction using two color separation filters, a color separation filter that is not used in the first line sensor, and a color separation filter in the first line. It consists of a second row of line sensors in which light-receiving elements are arranged alternately in the main scanning direction using one of the two color separation filters used; The color separation filters used for both of the eye line sensors are arranged so that they have the same phase in the sub-scanning direction, and (2) the plurality of filters are green, red, and blue filters, and the first row It is characterized by the fact that the filters used for both the and second row are blue filters. Hereinafter, the present invention will be explained based on examples.

FIG. 1 is a block diagram for explaining an embodiment of an image reading apparatus according to the present invention. In the figure, 1 is a line sensor in two rows, 2, 3, 4, and 5 are sampling and holding circuits, and 6 is a block diagram for explaining an embodiment of an image reading device according to the present invention. is an adder circuit.

FIG. 2 is a diagram showing a light-receiving portion of an image reading device, in which a color filter of one color is arranged to cover one light-receiving portion. Regarding the filter arrangement, red filters (R) and blue filters (B) are arranged alternately in the first column, and green filters (G) and blue filters are arranged alternately in the second column. ing. Furthermore, the blue filters in the first row and the blue filters in the second row are arranged in the same phase. The signals obtained from the two rows of line sensors are the R signal and B signal in the first row.
The second column of signals is divided into a B signal and a G signal, and each is sampled and held. The B signals sampled and held in both the first and second columns are divided into 1/1 by the adder circuit 6.
By adding with a weight of 2, R, G, and B signals are obtained.

In the configuration of the present invention, the number of pixels in the main scanning direction is N.
Then, one row of line sensors requires 2N light-receiving elements, and the number of pixels in the main scanning direction is 3/2 that of the configuration in which R, G, and B are arranged in one horizontal row as shown in Figure 5, resulting in high resolution. is obtained. In addition, in the configurations shown in FIGS. 7 and 9, the number of pixels is greater than that in FIG. 5 because pixels are read at sampling intervals for green (G) or white (W), but the number of samplings for red and blue is increased. Because red and blue are used as color information for both the front and rear pixels, even if the pixel resolution is below the green Nyquist frequency, in the case of an image that is above the red and blue sampling Nyquist frequency. Since the phases of red and blue are out of phase by 1/2 period, color shift and moiré occur between red and blue. Due to the spatial frequency characteristics of the visual system, it is thought that the resolution of red and blue is lower than that of green, which contains a lot of luminance information, making it difficult to see. In images containing red and blue color moire, both red and blue color moiré appear, so if the input pixels and resolution are the same, even images that cannot be resolved by the human eye will have magenta, which is an additive color mixture of red and blue. Color appears throughout.

In the present invention, since R, G, and B are read at the same resolution, moiré does not occur in image parts with low frequencies as described above, and moiré does not occur in images near the Nyquist frequency of R, G, and B. In this case, red and green are in phase, so no shift occurs, and the mixed color of red and green is yellow, so the colors that cause the phase shift that causes color shift are blue and yellow. Because they are complementary colors, when humans see them they cannot resolve them and when they are mixed, they become colorless. Therefore, when reading black and white, new colors like the one above are displayed in image parts that contain frequency components that are higher than the human resolution. does not appear. Furthermore, since the light receiving element has high sensitivity on the long wavelength side and low sensitivity on the short wavelength side, the blue output has a poor S/N ratio. Furthermore, most illumination systems that illuminate the original during input have weak power on the short wavelength side. In the present invention, since the blue signal is read by twice as many light receiving elements as the red and green signals, a large amount of light can be obtained and the S/N ratio can be increased.

FIG. 3 is a diagram showing another embodiment of the image reading device according to the present invention. In the figure, 1a is a line sensor in the first row, 1b is a line sensor in the second row, and 10 and 11 are A/Ds. A conversion circuit, 12 and 13 are line buffers, 15 and 16 are delay circuits, 17 is a digital addition circuit, and other parts having the same functions as in FIG. 1 are given the same reference numerals. In order to read the sensors in the first and second rows in the same phase in the sub-scanning direction, when scanning the document or sensor in the sub-scanning direction, the reading positions of the documents in the first and second rows may not match. This method uses the output of In this case, there is no positional shift between the first and second columns in the sub-scanning direction, and color shift in the sub-scanning direction is also eliminated.

FIG. 4 is a diagram showing still another embodiment of the image reading device according to the present invention, in which the image reading device has a three-row structure with each of the three colors as the light-receiving element rows as shown in FIG. In the figure,
1c is the line sensor of the first row, 1d is the line sensor of the second row, 1e is the line sensor of the third row, 20, 21, 22
is a sampling hold circuit, 25, 26, 27 are A/
D conversion circuit, 30, 32, 34 are line buffers, 31
, 33 and 35 are delay circuits. The line sensor shown in Figure 6 can obtain high-quality images in terms of high density and no color shift because the number of light-receiving elements matches the number of pixels, but since three rows of sensors are required, the entire sensor As the size of the line increases, three line buffers are required to bring the three rows of sensors into the same phase as shown in FIG. However, in the method of the present invention, two line buffers are sufficient. The capacity of the line buffer can be reduced to 2/3 of that in FIG. 7 if the number of output pixels is the same (the number of light receiving elements is twice as large as the sensor), and to 1/3 if the number of light receiving elements of the sensor is the same.

[0011]

[Effects] As is clear from the above description, the present invention has the following effects. (1) Effects on claim 1: Using line sensors arranged in two rows in the sub-scanning direction, two color filters are arranged alternately in the first row, and the filters of the first row are arranged in the second row. It has a configuration in which two color filters, one of the two color filters and a different color filter from the first row, are arranged alternately, and are used in both the first and second row sensors. Since the color filters are arranged in the same phase in the sub-scanning direction, the S/ of the color output used for both the first and second row sensors is
In addition to improving the N ratio, the sampling pitch of all colors is the same, and colors that are out of phase are complementary colors, so when output as an image, high-resolution color with less noticeable moiré is possible. I get a signal. (2) Effect on claim 2: Since the color used for both the first and second row sensors is blue, the S/N ratio of blue on the short wavelength side, where the sensitivity of the illumination system and light receiving element is weak, is reduced. This improves the accuracy of blue, which tends to affect color tone.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram for explaining an embodiment of an image reading device according to the present invention.

FIG. 2 is a diagram showing a light receiving part of the image reading device.

FIG. 3 is a diagram showing another embodiment of the image reading device according to the present invention.

FIG. 4 is a diagram showing still another embodiment of the image reading device according to the present invention.

FIG. 5 is a diagram showing a configuration of a light receiving element in which three colors are sequentially arranged.

FIG. 6 is a diagram illustrating an example in which three colors are used as respective light-receiving element rows.

FIG. 7 is a diagram showing a two-row configuration in which G filters are added among the three colors RGB.

FIG. 8 is a diagram showing a single row configuration in which G filters are increased among the three colors RGB.

FIG. 9 is a diagram showing an example in which one column is configured with one color filter and the other column is configured with two color filters.

[Explanation of symbols]

1...Two rows of line sensors, 2, 3, 4, 5...Sampling hold circuit, 6...Addition circuit.

Claims (2)

[Claims] 1. A line image composed of color separation filters of a plurality of different colors, color light receiving elements each arranged so that one filter of the color separation filter covers one light receiving surface, and the light receiving element. In the color image reading device, the plurality of color separation filters have a filter configuration in which the arrangement density of the color filters is varied depending on the color, and the plurality of color separation filters include color separation filters of three colors, and the color separation filters of three colors; A first row of line sensors in which light-receiving elements are arranged alternately in the main scanning direction using color separation filters of two of the three colors of the separation filters, and a color separation filter that is not used in the first row of line sensors. The first line consists of a second line sensor in which light-receiving elements are arranged alternately in the main scanning direction, using one color separation filter of the two color separation filters used in the first line. An image reading device characterized in that color separation filters used for both the sensor and the second row line sensor are arranged so that they have the same phase in the sub-scanning direction. 2. The image reading device according to claim 1, wherein the plurality of filters are green, red, and blue filters, and the filters used in both the first and second rows are blue filters.