JPH0399574A - Color image sensor - Google Patents

Abstract

PURPOSE:To read in the monochroic mode at a read density thrice that of the reading in the color mode by arranging photoelectric conversion elements corresponding to 3 unit line sensors while being deviated at a pitch of 1/3 element in the main scanning direction. CONSTITUTION:Unit line sensors 2a, 2b, 2c each comprising n-set of photoelectric conversion elements at an element pitch (d) on a line in the main scanning direction are arranged in parallel and color filters R, G, B are arranged respectively on the elements. Moreover, the elements of each line sensor are deviated by 1/3d in the main scanning direction, and the distance D between the sensors is selected as 3d. In the case of reading a monochroic picture, the output of each sensor is normalized based on the level of a white reference. Since the elements are arranged while being deviated by 1/3d, when outputs of each unit line sensor are synthesized as R1, G1, B1, R2, G2, B2, the monochroic picture is read with the resolution thrice that at the time of reading in the color mode.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a color image sensor, and particularly relates to a color image sensor that can read images in monotone.

[Prior Art] Conventionally, as a color solid-state image sensor used in a two-dimensional color document reading device, three types of color separation color filters (hereinafter referred to as color filters) are arranged dot-sequentially on one line sensor. What is known as a sequential array sensor is known.

This is a method in which three adjacent light-receiving elements are treated as one set when reading a color image, and when reading a monochrome image in which the image is read as monotone data, one light-receiving element is regarded as one set. It can be read at 3 times the resolution.

In addition, in order to increase the color reading resolution of the single line sensor mentioned above, three line sensors are arranged in parallel at a predetermined interval in the sub-scanning direction perpendicular to the main-scanning direction. Separation of each color has also been done. According to this method, an image at any position in the main scanning direction can always be separated by three color filters. Also 3
Monochrome image reading can be performed by using one of the two line sensors.

[Problem] However, although the color image sensor mentioned above triples the number of light-receiving elements with three line sensors and triples the resolution when reading color images, the resolution when reading monochrome images does not increase. There was a problem.

[Means for solving the problem] In order to solve the problem, the present invention provides that the corresponding photoelectric conversion elements of each line sensor are arranged so as to be shifted from each other by 1/3 element pitch in the main scanning direction. The resolution when reading a monochrome image is compared to 3 when reading a color image.
Improve twice as much.

[Example] FIG. 1 shows an example of the present invention. FIG. 2 is a diagram showing the spectral transmission characteristics of the RGB filter.

In the figure, on the semiconductor substrate 1, a first unit line sensor 2a, a second unit line sensor 2b, and a third unit line sensor 2c are arranged at a distance of D in the sub-scanning direction (Y direction) perpendicular to the main scanning direction. They are arranged parallel to each other, separated by These three unit line sensors 2a, 2b+2c are formed by arranging n photoelectric conversion elements made of, for example, PN junction photodiodes, in a straight line in the main scanning direction (X direction) with predetermined elements and gaps d. It is. R (red) filters RIR2, R, . . . , Rn, which are first color filters, are successively arranged on each photoelectric conversion element of the first unit line sensor. Further, G (green) filters G, , G2 . G.

Gn is also the third color filter B (blue)
Filter Bll B2. Bs, . . . , Bn are consecutively arranged. In addition, the mutual positional relationship in the main scanning direction of the photoelectric conversion elements corresponding to each unit line sensor is
With reference to the unit line sensor, the second unit line sensor is shifted by d/3, and the third unit line sensor is shifted by 2d/3 in the same direction.

Here, on the semiconductor substrate 1, in the case of a CCD, each unit line sensor 2. ．． 2b, 2. , a vertical charge transfer unit that transfers the charge generated in each photoelectric conversion element 3 and a charge transfer type shift register that outputs the charge of each pixel transferred in parallel to a charge transfer type shift register that serially outputs the charge generated in each photoelectric conversion element 3. A shift register is located. However, since it has no bearing on the gist of the present invention, the illustration is omitted.

Incidentally, it is generally desirable that the distance between each unit line sensor 2a, 2b2c be an integral multiple of the reading pitch in the sub-scanning direction (Y direction). The smaller this distance is, the smaller the capacity of the line memory for correction is required.

Next, the operation of the color image sensor according to this embodiment configured as described above will be explained. An optical image from a read document (not shown) is read by three unit line sensors as it is scanned in the Y direction. Now, if the distance between the unit line sensors is 3 line pitches (D=3d), the data for the first unit line sensor read first is obtained after reading 7 lines in the sub-scanning direction. This means that there are three colors, RGB.

When reading a monochrome original as monotone data, the output of each sensor is normalized based on the level at which each sensor reads a white reference (not shown). Thereby, the output of each unit line sensor can be treated equally as luminance data of a monochrome image. The corresponding photoelectric conversion elements of the three unit line sensors are shifted by 1/3 element pitch in the main scanning direction, so the output of each unit line sensor is
R1・Gt, B+, R2・G2・B2・°・
By combining RN, GN, and BN, it is possible to read a monochrome image with three times the resolution of color reading.

Further, as another combination of color filters, as shown in FIG. 3, a combination of complementary color filters shown in the spectral sensitivity characteristics of FIG. 4 can be considered. By arranging a cyan (C) filter as the first color filter, a green (G) filter as the second color filter, and a yellow (Y) filter as the third color filter, the same effect can be achieved in a wider area than the RGB system. can be realized. When using this complementary color filter, after reading (cyan-green)
, (Yellow-Clean) calculation is required to derive R and B, but since each color filter can transmit light in a wider wavelength range, the reading speed can be made faster.

When performing monochrome reading using this combination of complementary color filters, the green signal level is too low compared to the yellow and cyan signals, and if each signal is normalized by its white level, the gradation will drop. Therefore, when reading in monotone, by making the spectral distribution of the light irradiated on the sensor and the spectral transmittance distribution of the green filter similar to each other, it is necessary to make the spectral distribution of the light irradiated on each line sensor It is very useful to have approximately equal output levels. One way to do this is to use a mechanism in which a green filter is inserted into the optical system only when reading the original in monotone, or to prepare multiple light sources with different spectral distributions and turn them on only when reading the original in monotone. There are methods such as switching the light source to a green one.

By the way, in the examples shown in FIGS. 1 and 3, 2/3 of the reading area of each photoelectric conversion element of the three unit line sensors overlaps each other in the main scanning direction (X direction), so the pixel Resolution of several minutes cannot be obtained. Therefore, as shown in Fig. 5, the reading area of each photoelectric conversion element is
We propose a method to increase the resolution by shortening the length in the direction (direction). How to reduce the overlapping portion in the main scanning direction is determined by balancing the reduction in sensitivity due to a reduction in the reading area of the photoelectric conversion element and the improvement in resolution in the main scanning direction.

Further, it is preferable for the photoelectric conversion element of each unit line sensor that the aperture ratio of the light receiving area in the main scanning direction is in the range of 33% to 90% for monochrome reading.

The present invention can be applied to various unit line sensors such as CCD line sensors, BBD line sensors, and photodiodes.

[Effect of the invention 1 As described above, according to the present invention, the RG for color reading
By arranging the corresponding photoelectric conversion elements of the three unit line sensors equipped with Ba or CGYB color filters by shifting them by 1/3 element pitch in the main scanning direction, the reading speed is three times that of color reading. The reading density enables monochrome reading.

[Brief explanation of drawings]

FIG. 1 is a plan view showing the configuration of a color image sensor according to an embodiment of the present invention. FIG. 2 is a diagram showing the spectral transmission characteristics of the RGB filter used in the above embodiment. FIG. 3 is a plan view showing the configuration of a color image sensor according to another embodiment of the present invention. FIG. 4 is a diagram showing the spectral transmission characteristics of the CGY filter used in the above embodiment. FIG. 5 is a plan view for explaining a method of reducing the overlapping reading areas of each photoelectric conversion element in the main scanning direction. l...Semiconductor substrate 2a...First unit line sensor 2b...Second unit line sensor 2C...Third unit line sensor 3...Photoelectric conversion element 142 Pi fiffi

Claims (4)

[Claims] (1) Three unit line sensors, each consisting of a plurality of photoelectric conversion elements that generate electrical signals in response to light, arranged in a straight line in the main scanning direction, are arranged in parallel, and the light is split onto the photoelectric conversion element of each line sensor. In a color image sensor in which three types of filters with different transmittance distributions are arranged, the corresponding photoelectric conversion elements of each line sensor are separated by 1/1 from each other in the main scanning direction.
A color image sensor characterized in that three elements are arranged so as to be shifted by a pitch. (2) Claim (1) characterized in that the first color filter on the photoelectric conversion element is a red filter, the second color filter is a green filter, and the third color filter is a blue filter. Color image sensor described in section. (3) Claim (1) characterized in that the first color filter on the photoelectric conversion element is a cyan filter, the second color filter is a green filter, and the third color filter is a yellow filter. Color image sensor described in section. (4) The photoelectric conversion element of each unit line sensor is characterized in that the aperture ratio of the light receiving area in the main scanning direction is in the range of 33% to 90%. color image sensor.