JPS58182365A - Reading method of color picture - Google Patents

Abstract

PURPOSE:To eliminate almost color shift in reading a color original picture, by providing a transparent body for light scattering having different refractive index in response to the wavelength of a light, and providing a chromatic aberration almost equal to a pitch of a color separation filter. CONSTITUTION:A picture light L including color information transmitted from the reading position of a color original 3 passes through a lens 4 and a light scattering plate 5 and the image is focused on an image sensor 1. The plate 5 is a plate having large color scattering, e.g., optical glass plate, and it is installed to an optical axis O obliquely so as to make a prescribed angle to the line direction of the image sensor 1. The light L through the lens 4 is changed for the optical path in response to the included wavelength at the plate 5 and formed on the image sensor 1 via a color separation filter 2 provided at each picture element 6 of the sensor 1.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of reading an original image using an image sensor, and more particularly to a color image reading method of accurately reading an image having color information using an image sensor.

Conventionally, when reading a color original using a facsimile machine, etc., three image sensors are used to split the image light into three directions using a half mirror, etc., and pass each beam of light through red, green, and blue filters to the image sensor. Attempts are being made to form an image on top. Furthermore, in color televisions and the like, each color is read separately using three image pickup tubes.

In such a method, it is necessary to accurately match the relative positions of the three image sensors, and if the positions of the three image sensors are slightly deviated, color misalignment will occur.
The image obtained by combining the obtained electrical signals becomes very unsightly. Therefore, such a method is almost impractical when high resolution is required for reading.

Another method for reading color images is to provide a color separation filter 2 on the surface of a single image sensor 1 as shown in FIG. 1, which is often used in relatively small color television cameras and the like. This is a 1fl image sensor 1
Immediately before the image sensor 1, a filter 2 of three colors of red, green, and blue is provided corresponding to each adjacent picture element, and the image of the color original 3 is focused on the image sensor 1 via the lens 4. Red, green,
This is to obtain an electrical signal corresponding to blue image light. This method requires that the positions of the image sensor 1 and the color separation filter 2 be precisely aligned, but once they are aligned accurately, there is little deviation and there is no need for any other adjustment, which is an advantage.

However, even with this method, the positions of the three color pixels of red, green, and blue are essentially different, so color shift is unavoidable.For example, in a one-dimensional COD image of 1728 pixels, When using the sensor 1, if three color filters 2 of red, green, and blue are arranged sequentially corresponding to each picture element as shown in Fig. 1, the number of picture elements of each color becomes 576 picture elements. .

As a result, if a document with a width of 210 mm, for example, is to be read, the width per picture element is 0.36 mm. However,
At this time, the reading positions of the three colors red, green, and blue are shifted from each other by 0.12 mm, which is a particularly serious drawback when inputting the signals of the three colors to a computer, etc., and performing logical operations. For example, when reading the edge part of the original image consisting of a white background and a black background, the red and green pixels read the white background, and the blue pixels read the black background. Then, even though there is no yellow part in the original image, the combined part will be calculated as yellow. When the original image is separated into colors and read in this way, if a color shift exists, a color that does not exist at all in the original image may be determined as if it exists.

In recent years, original color images have been read by image sensors and input into computers for pattern recognition, or logical operations by computers have been used to separate the colors into multiple colors to create color printing originals. Many attempts are being made to obtain hard copies using laser beam printers that are capable of printing. is particularly important.

An object of the present invention is to eliminate the drawbacks of the conventional color image reading method as described above, and to
The purpose is to provide a color image reading method that almost eliminates color shift, and its gist is that when the color of one color image point is reproduced by combining the outputs of a plurality of picture elements of an image sensor, A color separation filter with color selection characteristics for multiple colors is placed in front of the image sensor corresponding to each pixel of the image sensor, and a color separation filter with a refractive index that differs depending on the wavelength of the light is placed in the optical path for forming one image light. A transparent body for light dispersion is provided to give a chromatic aberration of approximately the same magnitude as the pitch of the color separation filters, image light of a corresponding color is incident on each color separation filter, and the color is determined based on the light amount of each picture element. This method is characterized by regeneration.

The method of the present invention will be explained in detail based on the illustrated embodiments below.

FIGS. 2 and 3 are diagrams of a first embodiment of the color image reading method according to the present invention. As shown in these drawings, image light containing color information emitted from the reading position of a color original 3 passes through a lens 4, passes through a light dispersion plate 5, and forms an image on an image sensor l. The light dispersion plate 5 is, for example, an optical glass plate with large chromatic dispersion, and is arranged obliquely with respect to the optical axis 0 so as to form a predetermined angle with the line direction of the image sensor 1. The optical path of the image light that has passed through the lens 4 is changed by a light dispersion plate 5 according to the contained wavelength, and is transmitted onto the image sensor 1 via a color separation filter 2 provided for each picture element 6 of the image sensor 1. will be imaged. Here, the light dispersion plate is set so that the magnitude of the deviation of the imaging point due to the difference in the refractive index of the center wavelength of the three colors red, green, and blue almost matches the difference in the position of the three colors of the color separation filter 2. By setting the thickness and angle of 5, the three picture elements 6r, 6g, and 6b adjacent to the image sensor 1 can be attached to the original 3.
It reads the red, green, and blue lights corresponding to the same point above and converts them into electrical signals.

More specifically, for each picture element 6 of the image sensor 1, a color separation filter 2 for selecting transmitted light is adhered to the surface thereof. That is, a red filter 2r is applied to the pixel 6r that emits an output corresponding to red, a green filter 2g is applied to the pixel 6g corresponding to green, and a blue filter 2b is applied to the pixel 6b corresponding to blue. Provide M15. Therefore, the line 3 on the original 3 corresponding to the line direction of the image sensor 1
The image light L1 from one point a enters the light dispersion plate 5 through the lens 4, and the refraction angle is changed by the light dispersion plate 5 according to the order of the wavelengths, and the image light Lrl centered on red light is produced.
The image light Lg+ centered on green light is applied to the filter 2rl.
image light Lb centered on blue light is applied to the filter 2g+,
are respectively incident on the filter 2b. And the respective filters 2rl, 2g1, 2bI
The light transmitted through the picture elements 8rl, 8g+, and
8J and is converted into an electrical signal. These picture elements 8r
The electrical signals obtained from 1, 8g, , and 13b1 are combined electrically into one set, and the colors are reproduced as a point image. Further, the image light L2 emitted from another point on the line 3a is similarly dispersed by the light dispersion plate 5, and the image light Lr2
, Lgz, and Lb2, they enter the filter 2 and the image sensor 1 and are reproduced as point images. However, the image light L3 emitted from a point midway between the points where the image light and L2 are emitted will also be dispersed by the light dispersion plate 5, but as is clear from FIG. , the light Lr3 centered on red light enters the filter 2g2 that selects green light, and this filter 21
will hardly be transmitted. Similarly, the image lights Lg3 and Lb3, which mainly consist of green light and blue light, also enter the filters 2'b2 and 2rl, so that they are not transmitted through the image elements 6b2 and 6rl, and the image light L3 is based on the image light L3. No output is obtained and it is not reproduced as an image. Further, the original 3 is sent in the direction of arrow A and is reproduced two-dimensionally as a color image.

Next, the above embodiment will be explained based on specific numerical examples. The image sensor l has 1728 reprinted picture elements,
A picture element 6 having a pitch of 13 gm is used, and red, green, and blue color separation filters 2r, 2g, and 2b are arranged alternately for each picture element 6. The light dispersion plate 5 has a refractive index nr=1.79609 and a wavelength of 54 nm for red light with a wavelength of 858 nm.
Refractive index ng=1.81265 for 6 nm green light,
Refractive index nb=1 for blue light with wavelength 486nf+
, 82775 is used.

Here, as shown in FIG. 3, the angle between the perpendicular to the surface of the light dispersion plate 5 and the optical axis 0, that is, the inclination angle of the light dispersion plate 5, is θ.
, the thickness of the light dispersion plate 5 is d, the size of the color shift that occurs is X,
The refractive index of the light dispersion plate 5 for the two wavelengths of light is na,
nb, and the refraction angles for these lights are θa and θb, the following relationship holds true.

d (tanθa −tanθb) e c
osθ=Xsinθ= na 6 5inoa = nb * sinθb Therefore, using these formulas, blue light L with a wavelength of 486 nm
2 picture elements 26 between b and 656 nm red light Lr
It is sufficient to set θ and d so that a color shift of gm occurs.
For example, when the inclination angle of the light dispersion plate 5 is selected to be θ; 30', the thickness d of the light dispersion plate 5 is 0, which is d=5.53 mm. At this time, the imaging position of the green light Lg with a wavelength of 546 nm is 4
The distance is 12.3 pm from the imaging position of the 86 nm blue light Lb, and the three color image lights Lr, Lg of red, green, and blue
, Lb can be varied at a pitch of approximately 13 pm.

FIG. 4 shows another embodiment, in which a prism 7 is used instead of the flat light dispersion plate 5 for dispersing image light, and a first lens 8 and a second lens are installed before and after the prism 7. 9, and the first lens 8 sets its focus on the original 3. Therefore, the image light that has passed through the first lens 8 becomes parallel light, whose refraction angle is changed according to the wavelength by the prism 7, and an image is formed on the image sensor 1 via the second lens 9. The operation and effect of this embodiment are exactly the same as those of the previous embodiment.

In the above-mentioned re-example, the -dimensional image sensor 1
Although a method using a two-dimensional image sensor has been described, it is possible to read the entire screen without moving the original image and the image sensor relative to each other. In this case, the simplest color separation filter pattern used in the two-dimensional image sensor is a striped pattern arranged in the line direction of the image sensor. That is, striped filters of three colors red, green, and blue may be provided in one direction so as to match the pitch of the picture elements. Further, in this case, the light dispersion transparent body having a different refractive index depending on the wavelength of light is arranged so as to be refracted in the direction of the stripes of the color separation filter, similarly to the illustrated embodiment. In addition to the above-mentioned stripe pattern, checkerboard patterns are known as the shapes of color separation filters used in two-dimensional image sensors. Any pattern can be applied as long as the patterns are repeatedly arranged in one direction according to the order of .

Image sensors that can be used in the method of the present invention include C
In addition to solid-state image sensors such as CD and MOS, image pickup tubes and the like can also be used, and various one-dimensional or two-dimensional image sensors can also be used. The image signal output from the image sensor can be input to a computer or the like and used for image pattern recognition, or it can be processed by a well-known color image signal processing circuit or the like and reproduced on a display device or the like. It is valid. Furthermore, the light dispersing transparent body having a different refractive index depending on the wavelength of light used in the present invention may be made of various optical glasses or materials such as acrylic synthetic resin.

In addition, in the above embodiment, the case where the reading is performed by separating into three colors of red, green, and blue was explained, but the same effect can be obtained even if a filter of other colors such as cyan is used instead of blue, and macenda is used instead of red. Colors can be reproduced. Furthermore, in the case of a color image that can be reproduced using only two colors, there is no problem in using a color separation filter for only two colors without daring to separate the image into three colors.

As described above, according to the color image reading method according to the present invention, it is possible to read and reproduce a color image with practically no color shift using one image sensor while reading the original image. It also has advantages such as not requiring delicate color adjustments unlike conventional reading methods using multiple image sensors.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of a conventional reading method, Fig. 2 and the following show an embodiment of a color image reading method according to the present invention, and Figs. 2 and 3 are explanations of the first embodiment. 4 are explanatory diagrams of the second embodiment. 1 is an image sensor, 2 is a color separation filter, 3 is a color original, 4, 7, 8 is a lens, 5 is a light dispersion plate, 6 is a picture element, 7 is a prism, and L is an image light. Patent applicant Canon Co., Ltd. Figure 111 Figure 3 Figure 114 Figure 319-22

Claims (1)

[Claims] 1. When reproducing the color of one color image point by combining the outputs of multiple picture elements of the image sensor, select multiple colors in front of the image sensor corresponding to each picture element of the image sensor. A color separation filter having a characteristic is arranged, and a light dispersion transparent body having a different refractive index depending on the wavelength of the light is provided in the optical path for forming an image light, and the size is approximately equal to the pitch of the color separation filter. A method for reading a color image, characterized in that image light of a corresponding color is incident on each color separation filter, and colors are reproduced based on the amount of light of each picture element. 2. Repeatingly forming a plurality of picture element sets corresponding to the color separation filter in the line direction on the image sensor,
A method for reading a color image according to claim 1, wherein the color image is reproduced one-dimensionally. 3. The color image reading method according to claim 2, wherein a plurality of striped image sensors are arranged in parallel to reproduce a color image two-dimensionally. 4. The color image reading method according to claim 1, wherein the light dispersing transparent body is optically flat and forms a predetermined angle with respect to the line direction of the image sensor. 5. The method of reading a color image according to claim 1, wherein the light dispersing transparent body is a prism to provide chromatic aberration.