JP2585019B2 - Imaging device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an imaging device.

(Prior Art) As this type of conventional image pickup apparatus, there is, for example, one shown in FIG. In the figure, 1 is an image sensor, 2 is an amplifier, 3 is a horizontal low-pass filter circuit A, 4 is an addition circuit, 5 is an arithmetic circuit, 6 is a gamma correction circuit, 7 is a horizontal contour compensation circuit, and 8 is color. Signal processing circuit, 9 is an NTSC encoder, 10 is a vertical low-pass filter circuit, 12 is a horizontal low-pass filter circuit B, 14
Is a 1H delay device. FIG. 7 shows a color filter configuration of the image sensor 1, and FIG. 8 shows a response of a pixel signal corresponding to each color filter when achromatic light is input.

To explain the operation of this conventional apparatus, a pixel signal output from the image sensor 1 is synchronized by a 1H delay unit 14 for two lines, an average of the two lines is obtained by a vertical low-pass filter circuit 10, and a signal is obtained. Earn the SN ratio. Next, the modulation component (color signal component) by the color filter is removed by the horizontal low-pass filter A3, and the vertical contour compensation signal obtained by the horizontal low-pass filter B12 and the arithmetic circuit 5 is added. Then, the signal passes through the gamma correction circuit 6 and the horizontal contour compensation circuit 7 to become a luminance signal.
The color signal is extracted from the pixel signal by the color signal processing circuit 8 and a predetermined video signal is obtained by the NTSC encoder 9 using the luminance signal and the color signal.

(Problems to be Solved by the Invention) In the conventional configuration as described above, the amount of light incident is reduced by A, C in FIG.
In the region, there is no problem since the average value of the WG pixel and the average value of the Cy and Ye pixels match, but in the B region where some pixels are saturated, the Average and Cy ・ Ye
A difference occurs in the average value of pixels, and a luminance difference between scanning lines appears in the vertical contour compensation signal, thereby causing a problem that image quality is significantly reduced.

The present invention has been made in view of the above circumstances, and provides an imaging apparatus in which a decrease in image quality due to a luminance difference between scanning lines that occurs when some pixels are saturated is eliminated.

(Means for Solving the Problems) In view of the above, the present invention provides a method of generating a plurality of lines of pixel signals or signals obtained by calculating pixel signals of lines of an image sensor through a color filter for spatial modulation multiplexing of color components. A color low-pass filter circuit for reducing a modulation component by a color filter as an input, each clip circuit for clipping an output signal of each low-pass filter circuit at a predetermined same level, and an output of each clip circuit And an arithmetic circuit for obtaining a vertical contour compensation signal using the above.

(Operation) By passing the pixel signals of a plurality of lines of the image sensor through the low-pass filtering circuit and clipping the output of each low-pass filtering circuit at a predetermined same level, some pixels are saturated. The image quality is prevented from deteriorating except for the luminance difference between the scanning lines that occurs when the image is displayed.

(Embodiment) FIG. 1 shows an embodiment of the present invention, in which components similar to those of the above-mentioned conventional apparatus are denoted by the same reference numerals, and 11a and 11b are clipping circuits, and a horizontal low-pass filtering circuit B12a. , 12b are clipped at the same predetermined level.

Next, this operation will be described. First, a pixel signal output from the image pickup device 1 passes through the amplifier 2 and is synchronized by the 1H delay unit 14 for two lines. The color signal processing circuit 8, the vertical low-pass filtering circuit 10, the horizontal low-pass filtering The signals are input to the circuits B12a and B12b, respectively. The color signal is processed by the color signal processing circuit 8, and the luminance signal is processed by the vertical low-pass filter 10, the horizontal low-pass filter A3, the gamma correction circuit 6, and the horizontal contour compensation circuit 7.
The chrominance signal and the luminance signal are converted into predetermined NTSC video signals by the NTSC encoder 9. Up to this point, the configuration is the same as the conventional configuration shown in FIG.

Next, a description will be given of a vertical contour compensation signal that is a problem. First, pixel signals input to the horizontal low-pass filtering circuits B12a and 12b are, as shown in FIG. Responses (shown by broken lines) are different. When this pixel signal passes through the horizontal low-pass filtering circuits B12a and 12b,
As shown by the solid line in the figure, the WG line outputs the average value of the signals of the W and G pixels, and the CyYe line outputs the average value of the signals of the Cy and Ye pixels. If the horizontal low-pass filter B12a, 12b
Is directly connected to the arithmetic circuit 5, a level difference occurs between the WG line and the CyYe line in the region B where some pixels are saturated, which adversely affects the image quality. Therefore, when the response at which the W pixel saturates is equal to or less than the value of Cw, the outputs of the horizontal low-pass filtering circuits B12a and 12b are clipped by the clipping circuits 11a and 11b, so that the levels of the WG line and the CyYe line are adjusted. Get rid of the difference. Thus, it is possible to prevent the luminance difference between the scanning lines from occurring in the vertical contour compensation signal.

In practice, the luminance difference between the scanning lines is visible even when there is 1-2% of the image signal. Accordingly, by setting the clip value Cw to be slightly smaller than the position shown in FIG. 2, the occurrence of a level difference between scanning lines due to a change in the position of the W pixel saturation point due to an error in the pixel response of each circuit is also prevented. be able to.

The vertical contour compensation signal obtained in this way is input to the addition circuit 4, where the vertical contour compensation of the luminance signal is performed.

As described above, in this embodiment, the luminance difference between the scanning lines of the vertical contour compensation signal is obtained by passing the pixel signal through the low-pass filtering circuit and further restricting the signal of each scanning line at a predetermined same level. Can be prevented and image quality can be improved.

FIG. 3 shows another embodiment of the present invention. The difference from the embodiment shown in FIG. 1 is that, among the color filters for spatial modulation multiplexing of color components, particularly, the level difference between W and G pixels. The WG pixel correction circuit 13 is inserted in order to suppress the disturbance to the luminance signal due to the modulation component described above, and the color signal processing circuit 8 receives the pixel signal before the WG pixel correction circuit 13 as an input. Other signal processing is basically the same as that of the embodiment shown in FIG. The color filter configuration of the image sensor is the same as that shown in FIG.

Here, the operation of the WG pixel correction circuit 13 will be described.
The WG pixel correction circuit 13 creates a correction signal obtained by multiplying each signal level of the WG pixel by a constant so as to eliminate the level difference of the WG pixel signal, and replaces only the high frequency component of the pixel signal with the correction signal.
This is to reduce the jagged flicker at the edge of the image. FIG. 4 shows how the correction is performed by multiplying the pixel signal by the correction constant. FIG. 5 shows the response of the output of the WG pixel correction circuit 13 to the high-frequency components of each pixel when there is no clipping circuit 11a, 11b during achromatic imaging. The response to low frequencies is the same as in FIG.

In FIG. 5, when the input signal level is in the area A, there is no level difference between the W and G pixels, but in the area where the pixels are saturated.
In the case of B and C, a level difference occurs between the W and B pixels, so that jagged flicker occurs at the edge of the image in the high frequency component, and the average value of the WG line and CyYe in the low frequency component.
A difference occurs in the average value of the lines, resulting in a level difference between the scanning lines. If subsequent signal processing is performed as it is, the image quality will be significantly reduced, but the characteristics of the clipping circuits 11a and 11b will be changed to W.
If the point at which the pixel is saturated or a value lower than that is used as the clip value, the difference between the average value of the WG line and the average value of the CyYe line in the regions B and C is eliminated. As a result, the level difference between the scanning lines of the vertical contour compensation signal is eliminated, and deterioration of the image quality due to the level difference for each line is prevented.

Even when the WG pixel correction circuit 13 is used as in this embodiment, the pixel signals of a plurality of lines are passed through the low-pass filter circuits, and the signals of the respective lines are clipped at the same predetermined level. Accordingly, it is possible to prevent the occurrence of a level difference between scanning lines.

Note that the above embodiment is only for a color camera, but other imaging devices, such as a facsimile, a scanner,
It is also applicable to hard copy devices. Further, the same configuration can be obtained by using a plurality of 1H delay units and synchronizing pixel signals of three or more lines.

(Effects of the Invention) As described above, according to the present invention, it is possible to prevent a luminance difference between each scanning line that occurs when some pixels of the image sensor are saturated, and to reduce the image quality. Can be eliminated.

[Brief description of the drawings]

FIG. 1 is a block diagram of one embodiment of the present invention, FIG. 2 is a graph showing the relationship between the response of incident light and a pixel signal and the operation of a clipping circuit of the embodiment, and FIG. 3 is a block diagram of another embodiment. FIG. 4 is a diagram for explaining the operation of the WG pixel correction circuit, and FIG.
FIG. 6 is a graph showing the relationship between the incident light and the output response of the WG pixel correction circuit of another embodiment, FIG. 6 is a block diagram of a conventional imaging device, and FIG. 7 is a diagram showing a color filter configuration of an imaging device. FIG. 8 is a graph showing the relationship between the incident light and the response of the pixel signal in the conventional device. 1 ... image sensor, 5 ... arithmetic circuit, 11a, 11b ... clip circuit, 12a, 12b ... horizontal low-pass filter circuit B, 13 ... W
G pixel correction circuit.

Claims (1)

(57) [Claims] An image pickup device for performing image pickup via a color filter for spatial modulation multiplexing of color components receives, as input signals, pixel signals of a plurality of lines or signals obtained by calculating pixel signals of the lines, thereby reducing modulation components due to the color filters. A clipping circuit for clipping the output signal of the color low-pass filtering circuit at a predetermined same level, and an arithmetic circuit for obtaining a vertical contour compensation signal using the output of each clipping circuit. Imaging device.