JP2007311961A - Camera device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a camera device which redues the amount of information while suppressing deterioration in image quality even in an image including a large movement. <P>SOLUTION: The camera device comprises: an imaging means 10 of generating a video signal corresponding to imaging light of a subject; a sharpness adjusting means 21 of adjusting sharpness of the video signal; a contrast adjusting means 21 of adjusting a contrast; encoding means 34, 35 and 41 of encoding video signals from the sharpness adjusting means and contrast adjusting means; and a control means of controlling the sharpness adjusting means and contrast adjusting means so that predetermined amounts of video signals are supplied to the encoding means and the sharpness and contrast are adjusted simultaneously. When an image has a small movement, its outlines are emphasized with a normal contrast and sharpness, and set values of the contrast and sharpness are discriminatingly used for a particular scene to keep picture quality deterioration small, thereby improving a decrease in frame rate. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a camera device, and more particularly to a camera device that performs an encoding process on a video signal obtained by photographing a subject.

  Conventionally, in a camera device that shoots a subject and performs encoding processing on the obtained video signal, the compression ratio of the image and the image quality are in a trade-off relationship, and when obtaining a high compression ratio, the image quality must be sacrificed to some extent. I must. Furthermore, there is a trade-off relationship between improving the image quality for each image and bringing the movement of the subject in the image closer to a natural one even if the image quality is lowered. In this case, in general, priority is given to detecting the motion of the image and prioritizing improving the image quality of each frame by clarifying the outline when the motion is small, and conversely, if the motion is large, the image is filtered to the image of each frame. Even if the image quality is lowered by applying a priority, priority is given to smoothing the movement of the image.

  If there is an accelerated movement of the sharp edge of the subject in the image, the DCT (Discrete Cosine Transform) coefficient distribution increases on the wide area side in the block, which is expected to continue zero run in the next zigzag scan. The occurrence of non-zero quantized representative values increases in the second half of the scan. This is because high-frequency components have increased in the inter-frame difference data before DCT, and as a result, the amount of generated code in the entire image frame increases. For this reason, when the movement is intense, the transmission rate for communication is limited, so the frame rate has to be lowered accordingly, and when decoding on the receiving side, the movement in the image is not smooth. There is a problem that a poor quality image is reproduced.

  In order to solve this problem, for example, Patent Document 1 discloses that even when a subject with rapid motion is photographed, a video signal is encoded while improving the frame rate while minimizing deterioration in image quality as much as possible. The integrated representative value summation circuit calculates the integral value (summation) of the quantized representative value in the high frequency range, and the quantization circuit quantizes the summed value into, for example, an 8-bit summed value signal to obtain a serial bus interface, bidirectional serial It is supplied to the microcomputer via a bus, etc., and the microcomputer determines whether there are many non-zero quantized representative values based on this total value signal. If there are many non-zeros, sharpness is reduced to prevent a decrease in the frame rate. There has been proposed a camera device for lowering.

Japanese Patent Laid-Open No. 10-108063

  However, even the camera device described in Patent Document 1 has a problem in that in the case of an image having a large movement, a sufficient amount of information cannot be compressed only by adjusting the sharpness.

  Therefore, the present invention has been made in view of the problems in the conventional technology described above, and is a camera capable of reducing the amount of information while suppressing deterioration in image quality even in the case of an image having a large movement. An object is to provide an apparatus.

  In order to achieve the above object, the present invention provides a camera apparatus, an imaging unit that generates a video signal corresponding to imaging light of a subject, a sharpness adjustment unit that adjusts the sharpness of the video signal, A contrast adjusting means for adjusting contrast, an encoding means for encoding the video signal from the sharpness adjusting means and the contrast adjusting means, and a predetermined amount of the video signal is supplied to the encoding means; The sharpness adjusting means and the control means for controlling the contrast adjusting means are provided so as to adjust the sharpness and the contrast at the same time.

  According to the present invention, the sharpness adjusting means and the contrast adjusting means are supplied by the control means so that a predetermined amount of the video signal is supplied to the encoding means, and the sharpness adjustment and the contrast adjustment are performed simultaneously. Since the control is performed, it is possible to reduce the amount of information while suppressing deterioration in image quality when shooting an image with a large movement or a complex image. Specifically, in the case of an image with a small amount of motion, normal contours and sharpness are set to enhance the outline, providing high-contrast high-quality images, and sharpness and contrast settings for specific scenes. By using them properly, it is possible to improve the decrease in the frame rate while keeping the image quality deterioration small.

  In the camera device, when the average value of the entire luminance component of the video signal generated by the imaging means is not less than the first set value and not more than the second set value, the average value is the first value. The contrast can be adjusted to be higher than in the case where the value is between the set value and the second set value. In bright places, the contrast is already low, so reducing the contrast has little effect. Therefore, it is not necessary to lower the contrast than when setting when the frame rate is lowered in a place of normal brightness. Thereby, there is little image quality degradation and it can improve the fall of a frame rate.

  In the camera device, when the average value of the entire luminance component of the video signal generated by the imaging means is equal to or less than a predetermined value, the sharpness is reduced more than when the average value exceeds a predetermined value. It can be adjusted smaller. Since noise is likely to appear in dark places, the noise can be made inconspicuous by reducing the sharpness further than the value set when the frame rate is lowered in a place with normal brightness for the purpose of suppressing this. .

  As described above, according to the present invention, it is possible to provide a camera device capable of reducing the amount of information while suppressing deterioration in image quality even for an image having a large movement.

  Next, embodiments of the present invention will be described with reference to the drawings.

  As shown in FIG. 1, the camera device according to the present invention is roughly divided into a camera unit (imaging unit) 10 that shoots a subject and generates an image, and an encoding that encodes an image generated by the camera unit 10. Part 30.

  The encoding unit 30 includes a luminance component determination circuit 31, an arithmetic circuit 32, a DCT circuit 33 that performs orthogonal transformation, a quantization circuit 34, a coefficient prediction circuit 35, an inverse quantization circuit 36, and a motion compensation circuit 37. A memory 38, an arithmetic circuit 39, an inverse DCT circuit 40, a variable length coding circuit 41, a frame rate detection circuit 42, a motion vector detection circuit 43, a camera control unit 20, and a frame rate / light / dark determination. The circuit 21 is configured.

  As shown in FIG. 2, the quantization circuit 34 includes a luminance / color difference component distribution circuit 50, a normal quantization table 51, an arithmetic circuit 52, and a high compression quantization table 53.

  The luminance component determination circuit 31 shown in FIG. 1 determines whether the place where the subject exists is a bright place or a dark place by taking the average of the entire luminance component supplied from the camera unit 10. To do.

  The arithmetic circuit 32 performs arithmetic processing using the video signal supplied from the luminance component determination circuit 31 as an addition signal, the prediction signal supplied from the motion compensation circuit 37 as a subtraction signal, and the obtained prediction error signal as a DCT circuit 33. To supply. Here, for example, the arithmetic circuit 32 takes a difference from the temporally forward image in the P picture (forward predicted image), and temporally forward or backward, or forward in the B picture (bidirectionally predicted image). By taking the difference from the stored image created from behind, the amount of information to be transmitted is reduced by reducing the redundancy in the time axis direction.

  The DCT circuit 33 performs a two-dimensional DCT (discrete cosine transform) on the prediction error signal from the arithmetic circuit 32 (or an original signal when prediction is not performed like a scene change) to remove spatial correlation, Concentrate energy on some coefficients. Specifically, the DCT circuit 33 converts 8 × 8 (= 64) image data into 8 × 8 (= 64) DCT coefficients.

  Here, when a subject with small motion is photographed and the inter-frame difference supplied to the DCT circuit 33 is small, the quantized representative value after the two-dimensional DCT conversion tends to be biased toward the head of the block, When a subject with a large amount of motion is photographed and the inter-frame difference supplied to the DCT circuit 33 is large, the quantized representative value after the two-dimensional DCT conversion tends to be biased toward the back of the block.

  Therefore, when zigzag scanning is performed during DCT conversion, the coefficient of image scan number 0 becomes a coefficient of DC (direct current) component, and the subsequent pixel scan numbers 1 to 63 become coefficients of AC (alternating current) component. At this time, the frequency components in the horizontal direction are concentrated toward the right side, and the frequency components in the vertical direction are concentrated toward the lower side. In addition, since all quantized representative values other than zero (non-zero) are encoded, the amount of generated code increases as the spectrum extends to a wide area, and the spectrum extends only from the low range to the mid range. Since there are few non-zeros, the amount of generated codes can be reduced.

  The quantization circuit 34 linearly quantizes the 64 DCT coefficients existing for each block with a different step size for each coefficient position, using a quantization table that defines the quantization step size for each coefficient. The quantized representative value obtained by this quantization is supplied to the coefficient prediction circuit 35 and the inverse quantization circuit 36. Further, the quantization table can be optimized for the luminance component and the color difference component according to the application. For example, as shown in FIG. 2, the amount of information is reduced by using a normal quantization table for the luminance component and a high compression quantization table for the color difference component. This uses the characteristic that the human eye is sensitive to changes in the luminance component but is not sensitive to changes in the color component, and can reduce the amount of information while suppressing deterioration in image quality. it can.

  The coefficient prediction circuit 35 quantizes the DCT coefficient, and then performs differential encoding called DC coefficient prediction. Also, differential encoding called AC coefficient prediction is performed on low-order AC coefficients by selection.

  The inverse quantization circuit 36 performs an inverse quantization process on the quantized representative value supplied from the quantization circuit 34 and supplies this to the inverse DCT circuit 40.

  The inverse DCT circuit 40 performs inverse DCT transform on the DCT coefficient supplied from the inverse quantization circuit 36 to decode the prediction error signal, and supplies the prediction error signal to the arithmetic circuit 39.

  The arithmetic circuit 39 adds and synthesizes the prediction error signal supplied from the inverse DCT circuit 40 and the prediction error signal motion-compensated by the motion compensation circuit 37, and supplies the synthesized prediction error signal to the memory 38.

  The memory 38 stores the prediction error signal for each block supplied from the arithmetic circuit 39 and supplies the prediction error signal to the motion compensation circuit 37 for each frame.

  The motion vector detection circuit 43 detects a two-dimensional motion vector based on the signals supplied from the camera unit 10 and the memory 38 and supplies the detection result to the motion compensation circuit 37.

  The motion compensation circuit 37 obtains a prediction signal by performing predetermined motion compensation on the prediction error signal for one frame read from the memory 38, and supplies this prediction signal to the arithmetic circuit 32 described above.

  The variable length coding circuit 41 performs code assignment (for example, Huffman coding) on the quantized representative value supplied from the coefficient prediction circuit 35 so as to shorten the average code length, and is thus obtained. Output compressed data.

  The frame rate detection circuit 42 counts the number of frames per second and obtains the current frame rate.

  The frame rate / brightness determination circuit 21 determines the current optimum contrast, sharpness setting value, and quantization table based on signals from the frame rate detection circuit 42 and the luminance component determination circuit 31, and uses the information as a camera. This is supplied to the control unit 20 and the quantization circuit 34.

  Based on the signal from the frame rate / brightness determination circuit 21, the camera control unit 20 performs register settings for the camera unit 10 via the camera control interface.

  Next, the operation of the camera apparatus having the above configuration will be described with reference to FIG.

  In step S1, the frame rate detection circuit 42 in FIG. 1 counts the number of frames per second, and supplies the current frame rate to the frame rate / brightness determination circuit 21.

  When the frame rate is less than a certain threshold Afps (Frame Per Second), the frame rate / brightness / darkness determination circuit 21 has a wide range due to the influence of an image with a large movement or an image in which local changes are discontinuous. It is determined that the image needs to be updated and the frame rate has decreased.

  After the decrease in the frame rate is detected, in step S 2, the second contrast and sharpness values that are dynamically lower than normal are set to the camera unit 10 via the camera control unit 20. With a large amount of movement, it is not possible to achieve a sufficient amount of information compression with sharpness alone. By reducing the contrast, the gradation difference of the entire screen can be reduced and the amount of information can be reduced. Rather than adjusting the sharpness and the contrast individually, the frame rate can be more effectively improved by adjusting both at the same time.

  Furthermore, in step S4, when the average value of the luminance component supplied from the luminance component determination circuit 31 is C or more, it is determined that the place is bright. In bright places, the contrast is already low, so reducing the contrast has little effect. Therefore, in step S5, it is not necessary to lower the contrast as compared with the case where the frame rate is lowered at the normal brightness (in the case of step S6). Thereby, there is little image quality degradation and the fall of a frame rate can be improved. This process operates with both a low frame rate flag and a bright place flag.

  In step S4, if the average value of the luminance components supplied from the luminance component determination circuit 31 is D or less, it is determined that the area is dark. Even in a dark place, as in a bright place, the contrast is already low, so reducing the contrast has little effect. Therefore, in step S7, it is not necessary to lower the contrast as compared with the case where the frame rate is lowered at the normal brightness (in the case of step S6). As a result, it is possible to suppress deterioration in image quality and to improve the frame rate. This process operates with both a low frame rate flag and a dark place flag. In addition, since noise is likely to appear in dark places, in order to suppress this, the noise can be made inconspicuous by lowering the sharpness further than the value set when the frame rate is lowered in a place with normal brightness. it can.

  Below, a setting image is demonstrated with the setting example of Table 1. FIG. It is assumed that the contrast and sharpness settings are each set to 100 when the frame rate is high, and the contrast and sharpness are reduced to 50 when the frame rate is reduced at normal brightness. Since there is no need to greatly reduce the contrast in a bright place and a dark place, each is set to 80. Furthermore, noise can be reduced by reducing the sharpness to 30 in a dark place.

  Further, in FIG. 3, when the frame rate becomes Bfps or less and a significant decrease in the frame rate is detected, the amount of information can be further compressed by controlling the use of the quantization table simultaneously with the sharpness and contrast control. Can do. When the frame rate is equal to or less than Bfps, the amount of information is reduced by using a standard quantization table for the luminance component and a high compression quantization table for the color difference component, as shown in FIG. This uses the characteristic that the human eye is sensitive to changes in the luminance component but is not sensitive to changes in the color component, and can reduce the amount of information while suppressing deterioration in image quality. it can.

  As described above, by adjusting the contrast, sharpness, and quantization table, it is possible to realize information amount compression with suppressed image quality deterioration, and to prevent a decrease in frame rate.

  If the frame rate in FIG. 3 exceeds a certain threshold Afps, the frame rate / brightness determination circuit 21 in FIG. 1 determines that an image with a small motion is being photographed, and in step S3, the normal rate is detected. Return to contrast, sharpness values and quantization tables. Thereby, from the camera part 10, an outline is emphasized and an image with high contrast can be reproduced.

It is a block diagram which shows the whole structure of the camera apparatus concerning this invention. It is a block diagram which shows the structure of the quantization circuit of the camera apparatus of FIG. It is a flowchart which shows operation | movement of the camera apparatus of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Camera part 20 Camera control part 21 Frame rate / brightness determination circuit 30 Encoding part 31 Luminance component determination circuit 32 Calculation circuit 33 DCT circuit 34 Quantization circuit 35 Coefficient prediction circuit 36 Inverse quantization circuit 37 Motion compensation circuit 38 Memory 39 Calculation Circuit 40 Inverse DCT circuit 41 Variable length coding circuit 42 Frame rate detection circuit 43 Motion vector detection circuit 50 Luminance / color difference component distribution 51 Normal quantization table 52 Arithmetic circuit 53 High compression quantization table

Claims (3)

Imaging means for generating a video signal corresponding to the imaging light of the subject;
Sharpness adjusting means for adjusting the sharpness of the video signal;
Contrast adjusting means for adjusting the contrast of the video signal;
Encoding means for encoding a video signal from the sharpness adjusting means and the contrast adjusting means;
Control means for controlling the sharpness adjusting means and the contrast adjusting means so that a predetermined amount of video signal is supplied to the encoding means, and the sharpness adjustment and the contrast adjustment are simultaneously performed. A camera device characterized by that.   When the average value of the entire luminance component of the video signal generated by the imaging means is not less than the first set value and not more than the second set value, the average value is equal to the first set value and the first set value. The camera device according to claim 1, wherein the camera device is adjusted so that the contrast is higher than that between the second set values.   When the average value of the entire luminance component of the video signal generated by the imaging means is less than or equal to a predetermined value, the sharpness is smaller than when the average value exceeds a predetermined value. The camera device according to claim 1, wherein the camera device is adjusted.

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