JPH11164089A - Color image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To relatively shorten the exposure time of a high-sensitivity line sensor and to uniform an S/N for each read color by making the frequency of a driving signal for reading one line through the line sensor for reading the first read color into the integer multiple of the frequency of a driving signal for a line sensor for reading the second read color. SOLUTION: A CCD image sensor 20 is provided with three line sensor having the same pixel size and number of pixels corresponding to red R, green G and blue B. These three line sensor are driven based on clocks outputted from respective driving signal generating means 31-33 for R, G and B but the frequency of the G clock is set to the double frequency of R and B clocks. Therefore, the exposure time of high-sensitivity line sensor for G becomes the half of line sensors for R and B. Thus, the output voltage of the line sensor for G is lowered and the S/N of respective three line sensors can be made uniform.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image reading apparatus such as a color image scanner and a color digital copying machine.

[0002]

2. Description of the Related Art As a color image reading apparatus, while scanning in a main scanning direction along a pixel column direction of an image sensor and a sub-scanning direction perpendicular thereto, the image sensor is scanned for each of a plurality of colors such as red, green, and blue. 2. Description of the Related Art There is conventionally known a configuration in which an image is read by exposing the image, and the read image is synthesized and output.

In this case, the image sensor is driven by a drive signal having a predetermined frequency, and the exposure of the image sensor and reading of one line are performed based on the signal.

Heretofore, the frequency of the driving signal for driving the image sensor has always been constant irrespective of the type of reading color, and therefore, the exposure time of the image sensor has also been constant irrespective of the type of reading color.

However, since the sensitivity of the read color differs for each color, the output value of the image sensor differs for the same exposure time, and the S / N ratio becomes non-uniform. As a result, a good image can be obtained. There is a disadvantage that it cannot be done.

Therefore, in order to eliminate the above-mentioned disadvantage, red,
In an image reading apparatus in which color filters of three primary colors of green and blue are arranged so as to face the image sensor, the color filters are switched, and scanning is performed for each color, and a signal for each color is output. There has been proposed a color image reading apparatus in which the frequency of a drive signal of an image sensor is changed to keep the output level of each color constant (Japanese Utility Model Publication No. Hei 7-15236).

[0007]

However, in the color image reading apparatus according to the above proposal, there is no specific disclosure about how to set the frequency of the drive signal of the image sensor for each color. May shift the reading timing of each color. When such a read timing shift occurs, there is a problem that an image processing circuit for correcting the shift becomes complicated.

In addition, since it is necessary to scan a plurality of times by switching the color filters, the overall reading speed is reduced, and it is necessary to switch the drive signal supplied to the image sensor every time the color filters are switched. Large-capacity memory means for storing images is also needed,
Circuits became increasingly complex.

SUMMARY OF THE INVENTION The present invention has been made in order to solve such a problem. In addition to making the S / N ratio uniform for each reading color, it is also possible to eliminate a shift in reading timing for each color. It is an object of the present invention to provide a color image reading apparatus which can perform reading at high speed and does not require switching of drive signals and large-capacity memory means.

[0010]

The object of the present invention is to provide a plurality of line sensors each of which reads a plurality of reading colors and has the same pixel size and the same number of pixels, and has a main scanning direction along a pixel column direction of the line sensors. An apparatus for scanning a color image by scanning in a sub-scanning direction perpendicular to the second scanning direction, wherein a frequency of a driving signal for reading one line of the line sensor for reading a first reading color is a second reading. Driving signal generating means for generating a driving signal for each line sensor so as to be an integral multiple of the frequency of the driving signal for the line sensor for reading the color; and reading the image read by each line sensor in the first reading color. Image data generating means for synthesizing at the resolution of the line sensor and outputting the image data as image data.

In such a color image reading apparatus, by setting the frequency of the drive signal of the line sensor having high sensitivity to the read color to an integral multiple of the frequency of the other line sensors, the exposure time of the line sensor having high sensitivity can be improved. Is relatively short, the difference between the output values of the line sensors is reduced, and S
/ N ratio becomes uniform.

Since the frequency of the driving signal of the line sensor for reading the first reading color and the frequency of the driving signal of the line sensor for reading the second reading color have an integral multiple, the driving signal of each line sensor is Are extremely easy to synchronize, and there is no shift in read timing.

Further, since a plurality of colors are read simultaneously by one scanning, there is no need to switch the color filters and perform the scanning a plurality of times. Therefore, the overall reading speed is increased, and the image data is supplied to the image sensor every time the color filters are switched. There is no need to switch the drive signal to be performed, and a large-capacity memory means for storing the read image is not required.

Further, the frequency of the drive signal of the line sensor for reading the first reading color is an integral multiple of the frequency of the driving signal of the line sensor for reading the second reading color.
While the line sensor that reads the first reading color reads one line, the line sensor that reads the first reading color reads a line that is an integral multiple of that. Then, the image read by each line sensor is synthesized at the resolution of the first line sensor and output as image data, so that the resolution in the sub-scanning direction is improved to an integral multiple of the case of reading at the frequency of the second line sensor. Thus, high-definition reading can be performed.

[0015]

FIG. 1 is a schematic configuration diagram of a color image reading apparatus according to an embodiment of the present invention.

In this color image reading apparatus, an automatic document feeder 4 is provided above the apparatus main body 1, and a document set on a document placing tray 3 is moved by a document feed roller 5 to a document reading position on a contact glass 2. And the document is discharged to a predetermined discharge position after reading.

In the apparatus main body 1, an illumination light source 6,
Reflecting mirror 7, first to third mirrors 8 to 10, imaging lens 11
And a three-line CCD image sensor 20. The CCD image sensor 20 includes three CCD line sensors corresponding to red (hereinafter referred to as “R”), green (hereinafter referred to as “G”), and blue (hereinafter referred to as “B”) in three rows. In addition, each line sensor is set to have the same pixel size and the same number of pixels (n), and is arranged so that the pixel arrangement direction is the paper thickness direction in FIG. Then, the reflected light from the original illuminated by the light source 6 is reflected by the first to third mirrors 8 to 10, passes through the imaging lens 11 and is input to the line sensors, and The reflecting mirror 7 and the first mirror 8 move integrally in the horizontal direction on the paper surface of FIG. 1 so that the original can be scanned in the main scanning direction along the pixel column direction of the line sensor and in the sub-scanning direction perpendicular thereto. Then, the color image of the document is read.

FIG. 2 is a block diagram showing a signal system of the color image reading apparatus according to one embodiment of the present invention, and FIG. 3 is a block diagram showing a configuration of the CCD image sensor and image forming means shown in FIG.

In FIG. 2, reference numeral 20 denotes a CCD image sensor, which is the same as that described with reference to FIG.

Reference numerals 31 to 33 denote three line sensors 21 to 2 for R, G and B in the CCD image sensor 20.
3 (shown in FIG. 3), three drive signal generating means for R, G, and B for generating clocks for driving the original 12, respectively. This is performed based on a clock. In this embodiment, the frequency of the G clock output from the G drive signal generating means 32 is the same as that of each of the R drive signal
The frequencies of the R clock and the B clock output from 1, 33 are set to twice (the period is 1/2), and each clock is output in a synchronized state. Specifically, in this embodiment, the frequency of the G clock is 2
0 MHz, the frequency of R clock and B clock is 10
MHz. Therefore, the reading of G by the G line sensor 22 is performed in half the time of reading R and B by the R and B line sensors 21 and 23, and the G line is read. The exposure time of the sensor 22 is also half of the exposure time of the R and B line sensors 21 and 23.

The first reason for setting the frequency of each clock as described above is as follows. That is, in general, R
The sensitivity of the CCD line sensor 22 for G is higher than that of the CCD line sensors 21 and 23 for B and B. Therefore, when illuminated by the same light source, the output of each line sensor differs considerably for each color as shown in FIG. 4 due to the difference in sensitivity of each line sensor. In this case, it is necessary to use a neutral density filter or shorten the exposure time so that the output of the G line sensor 22 does not exceed the saturation output voltage. However, R, G,
If the exposure time is shortened for each of the three B colors, the output voltage of the low-sensitivity B line sensor 23 becomes extremely low, and the S / N ratio of the output of the B line sensor 23 deteriorates compared to the output of the G line sensor 22. I do.

Therefore, by doubling the clock frequency of the G line sensor 22, the exposure time is halved and the output voltage of the G line sensor 22 is reduced as shown in FIG. Thereby, each line sensor 21-R for R, G, B
23, the difference between the output voltages is reduced, and the S / N ratio of each line sensor is made uniform.

The second reason why the frequency of each clock is set as described above is as follows. That is, by setting the frequency of the clock of the G line sensor 22 to be twice the frequency of the clocks of the R and B line sensors 21 and 23, the R and B lines are set as shown in FIGS. While the sensors 21 and 23 read one line, the G line sensor 22 reads two lines. As a result,
As shown in FIG. 8, the length of the reading area on the original read by one pixel of each line sensor in the sub-scanning direction is G half of R and B, and the reading density of G in the sub-scanning direction is R and B. It can be doubled. Therefore, the G line sensor 2
The resolution in the sub-scanning direction is increased by converting the resolutions of the R and B line sensors in accordance with the resolution (reading density) of 2.

In FIG. 2, reference numeral 40 denotes an image read by each of the line sensors 21 to 23,
Image data generating means for synthesizing based on the resolution of the image data and outputting as one image data. As shown in FIG. 3, the image data generating means 40 receives the line data read by the CCD line sensors 21 to 23 for a total of 5 lines.
It is provided with a plurality of line delay memories (FIFOs) 41 to 45, a total of two selectors 46 and 47, and one image synthesizing means 48.

The line delay memory corrects the amount of displacement of the three line sensors 21 to 23.
Two line sensors are provided for each of the R and B line sensors 21 and 23 driven by a 0 MHz drive clock. Then, the R and B line data read based on the 10 MHz driving clock are
And the data is alternately stored in the two line delay memories 41 and 42 and 44 and 45. In addition, each line sensor 2 for R and B
Since 1 and 23 are driven at 10 MHz, the same line data is stored in two line delay memories 41 and 42 and 44 and 45, respectively. The selectors 46 and 47 are connected to the two line delay memories 4.
1 and 42, and the line data stored in 44 and 45
It plays the role of alternately outputting at the timing of MHz. Accordingly, the selectors 46 and 47 output line data corresponding to the clock of 20 MHz.

For the G line sensor 22 driven by a 20 MHz clock, one line delay memory 43 is provided to store the line data from the G line sensor 22. I have.

The image synthesizing means 48 plays a role of synthesizing the line data from the line sensors 21 to 23 stored in the line delay memories 41 to 45.

Next, the operation of the image forming apparatus shown in FIGS.

The reflected light from the original 4 illuminated by the light source 6 is reflected by the first to third mirrors 8 to 10, passes through the imaging lens 11, and passes through three lines in the CCD image sensor 20. The signals are input to the sensors 21 to 23.

Each of the line sensors 21 to 23 is for R, G
And B are driven based on the clocks output from the drive signal generating means 31 to 33. Since the frequency of the G clock is set to twice the frequency of the R clock and the B clock, the sensitivity is increased. The exposure time of the high G line sensor 22 is half that of the other line sensors 21 and 23. Therefore, as shown in FIG. 5, the output voltage of the G line sensor 22 decreases, the difference between the output voltages of the R, G, and B line sensors 21 to 23 decreases, and the S / N of the three line sensors decreases. The ratio is made uniform.

Further, since the frequency of the G clock is set to twice the frequency of the R clock and the frequency of the B clock, as shown in FIGS. 6 and 7, the R and B line sensors 21 and 23 have one line. G line sensor 2 while reading
2 means that two lines are read. Therefore, as shown in FIG. 8, when the R and B line sensors 21 and 23 read r1 and b1 images in the sub-scanning direction, the G line sensor 22 outputs two images g11 and g12. Is read.

The line data of the images g11 and g12 read by the G line sensor 22 are sequentially stored in the line delay memory 43, subjected to a predetermined delay processing, and sequentially output. On the other hand, the line data relating to the image of r1 and b1 read by the line sensors 21 and 23 for R and B is 20 MH corresponding to g11 and g12.
At the read timing of z, the same data is alternately stored in the two line delay memories 41 and 42 and 44 and 45, respectively.

The g11 line data stored in the line delay memory 43 and the r1 and b1 line data correspondingly stored in the line delay memories 41 and 44 are synthesized by the image synthesizing means 48. The first line of image data 51 shown in FIG. 9 is generated and output. Next, the line data of g12 and the line data of r1 and b1 stored in the corresponding line delay memories 42 and 45 are synthesized by the image synthesis means 48,
The image data 52 of the second line shown in FIG. 9 is generated.

As can be understood from the above description, the R and B line sensors 21 and 23 are based on the resolution of the G line sensor 22 whose clock frequency is set to double.
Image data is generated by converting the resolution of the image data to match the resolution, so that the resolution in the sub-scanning direction is equal to the resolution of the line sensor 22 for G, and
This is twice the resolution of the line sensors 21 and 23 for B.
As a result, high quality reading can be performed without increasing the light amount of the light source.

Such an operation is sequentially repeated with the movement of the light source 6, the reflecting mirror 7 and the first mirror 8 in the sub-scanning direction, and the original is read. The image data output from the image data generating means 40 is subjected to predetermined image processing thereafter.

In the above embodiment, the frequency of the drive signal for the highly sensitive G line sensor 22 is set to twice the frequency of the drive signals for the R and B line sensors 21 and 23, but it is three times or more. It may be set to an integral multiple. in this case,
In the sub-scanning direction, image data may be generated based on the resolution of the line sensor set to three times or more. Further, for example, based on the frequency of the drive signal of the B line sensor having the lowest sensitivity, the frequency of the drive signal of the R line sensor having the next lowest sensitivity and the drive signal of the G line sensor having the highest sensitivity are substantially proportional to the sensitivity. The frequency of the drive signal of each line sensor may be set to a different value by multiplying the frequency by an integer.

Although not performed in the present embodiment, the adjustment of the gain of the line sensor and the adjustment of the light amount may be performed as needed.

[0038]

Since the present invention is dependent on the above, the frequency of the drive signal of the line sensor having high sensitivity to the reading color is set to an integral multiple of the frequency of the other line sensors, so that the sensitivity of the reading color can be improved. Exposure time of high line sensor can be relatively shortened, and S / N of each line sensor
The ratio can be made uniform.

Further, since the frequencies of the drive signals of the respective line sensors are in integral multiples, the respective drive signals can be synchronized with each other very easily, so that the read timing can be prevented from shifting and the processing circuit can be prevented. Can also be simplified.

Further, since a plurality of colors are read simultaneously by one scan, the overall reading speed is increased, and a drive signal to be supplied to the image sensor every time the color filter is switched, and a capacity for storing the read image. Large memory means can be eliminated.

Furthermore, since the image read by each line sensor is synthesized at the resolution of the line sensor for reading the first reading color and output as image data, the resolution in the sub-scanning direction can be improved, and high-definition reading can be performed. It becomes possible.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an entire color image reading apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of a reading system in the color image reading apparatus of FIG. 1;

FIG. 3 is a block diagram showing a configuration of a CCD image sensor and image data generating means of the block diagram of FIG. 2;

FIG. 4 is a graph showing the output voltage of each line sensor when the frequency of the drive signal is the same.

FIG. 5 is a graph showing an output voltage of each line sensor in the CCD image sensor shown in FIGS. 2 and 3;

FIG. 6 is a timing chart of read data of each line sensor.

FIG. 7 is a diagram showing a reading area of each line sensor.

FIG. 8 is a diagram showing a read area of one pixel of each line sensor.

FIG. 9 is a diagram showing a read area after image synthesis by the image data generating means shown in FIGS. 2 and 3;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Device main body 6 ... Light source 12 ... Document 20 ... CCD image sensor 21 ... R line sensor 22 ... G line sensor 23 ... B line sensor 31 ... R drive signal generating means 32 ... G drive signal generating means 33 .. B drive signal generating means 40 image data generating means 41 to 45 line delay memories 46 and 47 selector 48 image synthesizing means

Claims (1)

[Claims] A plurality of line sensors each of which reads a plurality of reading colors and has the same pixel size and the same number of pixels, and has a main scanning direction along a pixel column direction of the line sensor and a sub-scanning direction perpendicular thereto. An apparatus for scanning to read a color image, wherein a frequency of a driving signal for reading one line of the line sensor for reading a first reading color is a driving signal for a line sensor for reading a second reading color. Drive signal generating means for generating a drive signal for each line sensor so as to be an integral multiple of the frequency of the image, and combining the image read by each line sensor with the resolution of the line sensor for reading the first reading color. A color image reading apparatus comprising: image data generating means for outputting data as data.