JPH08338954A - Signal processing circuit for image pickup device - Google Patents

Abstract

PURPOSE: To eliminate the lowering of image quality caused by the difference of saturation characteristics generated by different color filters. CONSTITUTION: An image pickup device is provided with the prescribed plural- color filters. Besides, it is provided with a line separation circuit 14 separating a first horizontal scanning signal S1 and a second horizontal scanning signal S2 obtained by the combination of the different color filters, a delay circuit 15 delaying the signal S1 as long as one horizontal scanning term, sample-and- hold circuits 17 and 19 extracting a picture element signal as much as two picture elements of the first and the second signals S1 and S2, a comparator 20 comparing the picture element signal as much as two picture elements and a GCA 18 amplifying the second signal S2 by gain for eliminating a saturation state based on the output of the comparator 20. Thus, the levels of the first and the second horizontal scanning signals become identical. As the result, the unbalance of an included primary color component in the saturation state is eliminated and the raising of a scanning line is eliminated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal processing circuit of an image pickup device, and more particularly to processing of a video signal in an image pickup device in which filters of a predetermined color are regularly arranged in pixel units.

[0002]

2. Description of the Related Art A CCD (Charge Cou
An imaging device using a pled device) is well known, and examples of this imaging device include an electronic endoscope device and the like.
In this type of imaging device, for example, like a simultaneous electronic endoscope device, a color filter having a different color arrangement for each pixel is provided in the CCD, and a pixel signal is extracted via this color filter, From these signals, color difference signals, luminance signals, or video signals such as R (red), G (green), and B (blue) signals are formed.

FIG. 4A shows the arrangement of color filters formed on the element surface of the CCD 1 in the simultaneous electronic endoscope system. The color filters are arranged for each pixel as shown in the figure. The four colors of Cy (cyan), G (green), Ye (yellow), and Mg (magenta) are arranged as one set, and the color filters are repeatedly formed on the entire image pickup area by the arrangement of each set. . Then, the signal obtained in each pixel unit of the CCD 1 through this color filter is, for example, as shown in FIG. 4B, in the first horizontal scanning line ODD1 of the odd field, the pixel signals of the upper and lower two columns are The signals of Mg + Cy (mixed signal obtained by the color filters of Mg and Cy) and the signal of G + Ye are repeatedly output, and the next two columns of upper and lower pixel signals are added in the next horizontal scanning line ODD3. G + Cy signal, Ye + Mg
Signal is repeatedly output, and thereafter, the addition output is sequentially output to the lowest horizontal scanning line in the same manner.
Also in the even field, similarly, the signals G + Cy and Ye + Mg are output as the horizontal scanning line EVEN2, and the signals Mg + Cy and G + Ye are repeatedly output as the EVEN4 signal.

The output of the CCD 1 thus obtained is, for example, a luminance (Y) signal, an R (red) -Y signal which is a color difference signal, and a B signal by an arithmetic circuit such as a color separation circuit.
(Blue) -Y signal, or R (red), G (green), B (blue)
Signals are calculated, and these signals are converted into composite video signals by an encoder or the like and then output to the monitor. In this way, the image inside the observed body is displayed on the monitor.

[0005]

However, in the above-mentioned conventional image pickup apparatus, since the sensitivities of the colors of the color filters are different, the saturation characteristics of the CCD output are different, and under the condition that at least one color is saturated, There is a problem that scanning lines are raised in the image and the image quality is deteriorated. That is, FIG. 5 shows the photoelectric conversion characteristics of the CCD 1 in the red band, and the signals output from the CCD 1 using the respective color filters have saturation points VE1 in the order of the color filters Ye, Mg, Cy, and G. Will be reached. Then, in the addition signal for each horizontal scanning line, as shown in the photoelectric conversion characteristic of the red band in FIG. 5, a signal of Ye + Mg (addition signal),
The saturation point VE2 is reached in the order of the G + Ye signal, the Mg + Cy signal, and the G + Cy signal.

According to such a photoelectric conversion characteristic, when the incident light amount P1 shown in the figure is obtained, the signals of any color filters are not saturated and there is no problem, but when the light amount exceeds the light amount P2 in FIG. In the mixed signal of FIG. 6 as well, it enters an area in which the incident light amount P4 is exceeded and each color signal becomes unbalanced, and thus the signals of the primary color components R (red), G (green), and B (blue) are unbalanced. Becomes

FIGS. 7 to 9 show the level of the added signal when a subject of primary color is photographed, and FIG. 10 shows the level difference of the primary color signal between the horizontal scanning signals at the saturation level. Has been done. FIG. 7 is a mixed signal level when a red (R) color subject is photographed, FIG. 8 is a green (G) color subject, and FIG. 9 is a blue (B) color subject. Is. For example, in an electronic endoscope that captures a reddish subject, assuming that the saturation level is 0.008 in FIG. 7, the mixed signal Ye + Mg far exceeds the saturation level. And FIG.
Referring to the saturation level of 0.008 at 0, the R signal is much higher than the other signals. That is, when a red subject is photographed with an incident light amount at a saturation level,
As described above, between the horizontal scanning signal obtained by the combination of the color filters of Mg + Cy and G + Ye and the horizontal scanning signal obtained by the combination of the color filters of G + Cy and Ye + Mg,
There will be a large difference for the R signal.

FIG. 11 shows a display state of the monitor 2 having a saturated region. From the above, when the saturated halation 100 exists in the image of the monitor 2, scanning is performed around the saturated halation 100. A phenomenon that the line 101 is raised occurs, which deteriorates the image quality. For example, in an electronic endoscope apparatus for observing the inside of a living body, since a close-up image is taken of a reddish body cavity, the state shown in FIG. 7 is obtained, and the Ye + Mg signal containing a large amount of red component is saturated, and the red Scan lines will result.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a signal processing circuit of an image pickup apparatus which can eliminate the deterioration of image quality due to the difference in saturation characteristics caused by different color filters. Especially.

[0010]

In order to achieve the above object, the invention according to the first aspect is an image pickup apparatus having a color filter in which predetermined colors are formed in different combinations for each horizontal line, and output from an image pickup element. Per horizontal scanning signal
A separation circuit that separates horizontal scanning signals for each horizontal line of a combination of different color filters, a sampling circuit that extracts a predetermined pixel signal from a plurality of sets of horizontal scanning signals output from this separation circuit, and a sampling circuit that outputs these signals. Also, based on the output of this comparator and the comparator that compares the level of the specified pixel signal of the horizontal scanning signal of each set, the horizontal scanning signal of either set is amplified with a gain for eliminating the signal saturation state. A gain control circuit for processing and a combining circuit for combining the output of the gain control circuit and the other horizontal scanning signal are provided. According to a second aspect of the present invention, the image pickup device forms a first set and a second set of horizontal scanning signals, and the delay circuit delays the first horizontal scanning signal by one horizontal scanning period. The sampling circuit
The video signal is sampled every 2n (n: integer) pixels.

[0011]

According to the above construction, the repetitive signal of the signals obtained by the color filters of, for example, Mg + Cy (for one pixel) and G + Ye (for one pixel) is used as the first horizontal scanning signal G + C.
A repeated signal of the signals obtained by the color filters of y (for one pixel) and Ye + Mg (for one pixel) is obtained as the second set horizontal scanning signal. The horizontal scanning signals of the first and second sets are
For example, two pixels are sampled, these levels are compared, and the second set horizontal scanning signal is gain-controlled based on the voltage of the difference. Therefore, the levels of the first set and the second set of horizontal scanning signals obtained by different color filter combinations become the same, and as a result, when the signal of one of the color filters is saturated, the imbalance of the included color components is eliminated. As a result, the scanning line does not protrude.

When there are two sets of horizontal scanning signals obtained by combining different color filters as described above, sampling of the pixel signals may be performed every 2n (n: integer) pixels, for example, 4 pixels. Minutes may be sampled and their levels may be compared. Further, when there are three sets of horizontal scanning signals obtained by different combinations of color filters, it is sufficient to carry out every 3n (n: integer) pixels.

[0013]

1 shows the configuration of a signal processing circuit of an image pickup apparatus according to the first embodiment, and FIG. 2 shows each signal obtained in the embodiment. On the light receiving surface of the illustrated CCD 10,
The color filters having the arrangement shown in FIG. 4A are provided, and the color filters of Mg (magenta), G (green), Cy (cyan), and Ye (yellow) are arranged corresponding to the pixels. It Then, the driving clock is input from the timing generator 12 to the CCD 10, so that the addition signals in FIG. 4B are sequentially output.

The CCD 10 is provided with a line separation circuit 14 via an amplifier 13. The line separation circuit 1
In 4, the first set horizontal scanning signal S1 and the second set horizontal scanning signal S2 are separated by the line identification signal output from the timing generator 12. That is, as shown in FIG. 2A, the first horizontal scanning signal S1 is Mg + Cy.
(Mixed signal obtained by color filters of Mg and Cy), G +
The Ye signal becomes a repeated signal, and the second horizontal scanning signal S2 becomes a signal in which the G + Cy and Ye + Mg signals are repeated.

A delay circuit for delaying the first horizontal scanning signal S1 by one horizontal scanning period, a low pass filter 16, and a sample and hold circuit for sampling and holding the signals of two pixels are provided in the subsequent stage of the line separation circuit 14. 17 is provided. Also, by inputting the second set horizontal scanning signal S2,
Gain control amplifier for adjusting gain (GCA-Gain Contr
ol Amplifier) 18, and a sample hold circuit 19 that samples and holds signals for two pixels. The sample and hold circuits 17 and 19 receive the pixel sampling clock (2n) for sampling two pixels from the timing generator 12,
As shown in FIGS. 2C and 2D, signals of two pixels are extracted.

A comparator (differential amplifier) 20 for comparing the signal levels of two pixels of the first set horizontal scanning signal S1 and the second set horizontal scanning signal S2 is provided at the subsequent stage of the sample and hold circuits 17 and 19. The output of the comparator 20 [FIG. 2 (E)] is fed back to the GCA 18. That is, the GCA 18 amplifies the second set horizontal scanning signal S2 by the gain determined by the output of the comparator 20 to bring this signal to the same level as the first set horizontal scanning signal S1.

The low pass filter 16 and the GCA 18 described above.
A line synthesizing circuit 22 for synthesizing these output signals as odd and even field signals based on the line identification signal is provided in the subsequent stage.
In the subsequent stage, a signal processing circuit 23 that performs other image processing.
Is arranged.

The first embodiment has the above construction, and its operation will be described below. First, from the CCD 10, FIG.
As shown in (B), ODD1
Signals of Mg + Cy and G + Ye of the first horizontal scanning signal S
1 [Figure 2 (A)] shows G + Cy and Ye + M of ODD3.
The g signal is output as the second horizontal scanning signal S2 [FIG. 2 (B)], and in the even field, G + C of EVEN2.
y, Ye + Mg is the second horizontal scanning signal S2
The four signals of Mg + Cy and G + Ye are output as the first horizontal scanning signal S1. These horizontal scanning signals S1 and S
2 is input to the line separation circuit 14.

In the line separation circuit 14, the first horizontal scanning signal S1 and the second horizontal scanning signal S2 are separated based on the line identification signal, and the first horizontal scanning signal S1 is delayed by the delay circuit 15. The sample hold 1 is delayed by one horizontal scanning period and passed through the low pass filter 16.
7 is supplied. On the other hand, the second horizontal scanning signal S2 is GC
It is supplied to the sample hold 19 via A18. In these sample-holds 17 and 19, signals for two mixed pixels are extracted by the pixel sampling clock as shown in FIGS. 2C and 2D, and these pixel signals are output to the comparator 20. .

In this comparator 20, as shown in FIG.
The signal levels of both (C) and (D) are compared, and FIG.
The difference signal as shown in (E) is supplied to the GCA 18. Therefore, in this GCA 18, the gain of the second set horizontal scanning signal S2 is adjusted based on the above difference signal, and finally, as shown in FIG. A signal having the same level as that of the signal S1 is obtained.

Thereafter, the second horizontal scanning signal S2 is input to the line synthesizing circuit 22 and is synthesized with the first horizontal scanning signal S1 input from the low-pass filter 16 to be a field processing signal processing circuit. 23. The signal processing circuit 23 performs predetermined signal processing such as gamma processing, and outputs the processed video signal to the monitor.

As described above, the fact that the first set horizontal scanning signal S1 and the second set horizontal scanning signal S2 are at the same level means that the average value of two pixels of Mg + Cy and G + Ye and G + C.
This means that there is no level difference between the average values of the two pixels of y and Ye + Mg, and even if the signal of any one color is saturated, the saturated state is not apparent. That is, the conversion characteristics equivalent to the photoelectric conversion characteristics in the state where the incident light amount is within P2 in FIG. 5 and in the state where the incident light amount is within P4 in FIG. 6 are obtained. Therefore, the saturation state of the signal of the specific color is eliminated, and the protrusion of the scanning line shown in FIG. 11 is also eliminated.

FIG. 3 shows the configuration of the second embodiment, which is for digitally processing an image signal. That is, A / which inputs the output of the amplifier 13 of FIG.
A D converter 25, a selector 26 for separating the first horizontal scanning signal S1 and the second horizontal scanning signal S2, a line memory 27 for delaying the first horizontal scanning signal S1 by one horizontal scanning period, An arithmetic unit 28 for performing gain control using a multiplexer for two sets of horizontal scanning signals S2, and pixel signal extraction circuits 29, 30 for extracting signals for two pixels are provided. Further, a comparator 31 is provided at the subsequent stage of the pixel signal extraction circuits 29 and 30, and the output of the comparator 31 is supplied to the arithmetic unit 28. Further, a selector 32 as a line synthesizing circuit and a latch circuit 33 for adjusting the phase difference between the lines are provided.

According to the configurations of the above-described two embodiments, the first set horizontal scanning signal S1 separated by the selector 26 is delayed by the line memory 27 for one horizontal scanning period, and then the pixel signal extracting circuit 29 outputs it. A signal for 2 pixels of 2 (C) is obtained. On the other hand, in the second set horizontal scanning signal S2,
The signal for two pixels of (D) is extracted by the pixel signal extraction circuit 30, and both signals for these two pixels are compared by the comparator 31. In this comparator 31, for example, G + C
It is determined whether the two pixel signals y, Ye + Mg are larger or smaller than the two pixel signals Mg + Cy, G + Ye, and the determination signal is supplied to the arithmetic unit 28.

In the arithmetic unit 28, the gain coefficient corresponding to the determination signal is selected by the multiplexer, and this gain coefficient is multiplied by the second set horizontal scanning signal S2. And
These horizontal scanning signals S1 and S2 are combined by the selector 32 and the latch circuit 33 based on the line identification signal,
As a field signal, it is supplied to the same signal processing circuit as in FIG.

Thus, the signals of the first horizontal scanning signal S1 and the second horizontal scanning signal S2 obtained in the second embodiment are the average value of two pixels of Mg + Cy and G + Ye and G + C.
The average value of the two pixels of y and Ye + Mg is set to the same level. According to the digital processing of the second embodiment, there is an advantage that the circuit scale is reduced.

In the first embodiment described above, the delay circuit 15 for delaying the first horizontal scanning signal S1 is provided with the sample hold 17
However, the delay circuit 15 can also be arranged after the sample hold 17. Further, the GCA 18 of the first embodiment and the arithmetic unit 28 of the second embodiment are arranged to adjust the gain of the second horizontal scanning signal S2.
The gain of the first horizontal scanning signal S1 may be adjusted.

[0028]

As described above, according to the present invention,
An image pickup device having color filters of a predetermined plurality of colors separates horizontal scanning signals for each horizontal line of a combination of different color filters, and extracts pixel signals of, for example, two pixels from the plurality of separated horizontal scanning signals. Then, the saturation state is eliminated by amplifying one of the horizontal scanning signals of one set, so that the embossing of the scanning line caused by the difference in the saturation characteristics between the different color filter combinations is reduced. As a result, it is possible to eliminate the deterioration in image quality.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a signal processing circuit of an image pickup apparatus according to a first embodiment of the present invention.

FIG. 2 is a signal waveform diagram showing the operation of the embodiment.

FIG. 3 is a block diagram showing a configuration of a signal processing circuit of the image pickup apparatus according to the second embodiment.

FIG. 4 is a diagram showing an example of an arrangement of color filters in the related art and the present invention [FIG. (A)] and a read state [FIG. (B)] in each horizontal scanning line.

FIG. 5 is a graph showing saturation characteristics of each color of a conventional color filter.

FIG. 6 is a graph showing a saturation characteristic of an addition signal.

FIG. 7 is a spectral distribution characteristic diagram of a mixed signal when a red subject is photographed.

FIG. 8 is a spectral distribution characteristic diagram of a mixed signal when a green subject is photographed.

FIG. 9 is a spectral distribution characteristic diagram of a mixed signal when a blue subject is photographed.

FIG. 10 is a graph showing differences in primary color components between Mg + Cy, G + Ye signals and G + Cy, Ye + Mg signals at a saturation level.

FIG. 11 is a diagram showing a state of image quality deterioration due to conventional signal saturation.

[Explanation of symbols]

 1, 10 ... CCD, 14 ... Line separation circuit, 15 ... Delay circuit, 17, 19 ... Sample hold circuit, 18 ... Gain control amplifier (GCA), 20, 31 ... Comparator, 22 ... Line combination circuit, 26, 32 ... Selector, 27 ... Line memory, 28 ... Operation part, 29, 30 ... Pixel signal extraction circuit.

Claims (2)

[Claims] 1. An image pickup apparatus having a color filter in which a predetermined color is formed in a different combination for each horizontal line, and a horizontal scanning signal is output for each horizontal line of a combination of different color filters for a horizontal scanning signal output from an image pickup device. A separation circuit for separating, a sampling circuit for extracting a predetermined pixel signal from a plurality of sets of horizontal scanning signals output from the separation circuit, and a level of a predetermined pixel signal of each set of horizontal scanning signals output from the sampling circuit And a gain control circuit that amplifies a set of horizontal scanning signals with a gain for eliminating the signal saturation state based on the output of this comparator, and the output of this gain control circuit. A signal processing circuit for an image pickup device, comprising: a synthesizing circuit for synthesizing the other horizontal scanning signal. 2. The image pickup device forms a first set and a second set of horizontal scanning signals, the delay circuit delays the first horizontal scanning signal by one horizontal scanning period, and the sampling circuit: The signal processing circuit of the image pickup device according to claim 1, wherein the video signal is sampled for every 2n (n: integer) pixels.