JP2001203910A - Video signal processor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a video signal processor which can uniformly and effectively widen gradations of an image having a high-luminance and a low-luminance part nearby the center of a screen. SOLUTION: When the screen has low luminance at its center part, the coefficient is set >=1 at the center part, decreased stepwise toward the peripheral part, and set <=1 at the peripheral part. When the screen has high luminance at the center part, the coefficient is set <=1 at the center part, increased stepwise toward the peripheral part, and set >=1 at the peripheral part. Then the coefficient is set to LUT 22, a multiplying circuit 23 multiplies an input video signal corresponding to a screen position by the multiplier, and after a clip circuit 24 clips an overflow part, a gamma correcting circuit 25 performs nonlinear processing. Consequently, video can be displayed on a screen where a high- luminance and a low-luminance area are both present without spoiling their gradational representations.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video signal processing apparatus in an image pickup apparatus for picking up an image of a subject illuminated by illumination light from a light source device, and more particularly, to a gradation expression of an image in which a high luminance portion and a low luminance portion are mixed. The present invention relates to a video signal processing device that improves the image quality.

[0002]

2. Description of the Related Art As an image pickup apparatus provided with a light source device, there is an electronic endoscope using a solid-state image pickup device such as a CCD as an image pickup means. The electronic endoscope sequentially illuminates a subject with illumination light having different wavelengths such as red, green, and blue, and synthesizes a component image captured under illumination with illumination light of each wavelength to produce a color image. And a simultaneous type in which a subject is illuminated with white light and a color image is obtained by a mosaic color filter arranged in front of the imaging surface of a solid-state imaging device. In each case, the subject is illuminated by a light source device unique to the endoscope system using halogen or xenon, but these light source devices can automatically adjust the illuminance level by detecting the brightness of the screen. .

However, when an image of a tubular part in a living body is taken as an object using an endoscope, for example, even if the amount of illumination light is increased, the depth of the deep tube at the center of the screen becomes low due to the structure of the object. At the same time, the periphery of the screen becomes a high-brightness state called overexposure, making it difficult to observe. In addition, when a wide area such as a wall surface in a living body is set as a subject, the brightness of the central portion of the screen is automatically adjusted to an appropriate illuminance level by the dimming function of the light source device, but the peripheral portion is sufficiently adjusted. Since the amount of light cannot be obtained, the gradation expression may be poor at low luminance.

In order to solve such a problem of gradation expression, for example, in Japanese Patent Laid-Open No. 6-30301, a difference value between input and output signals before and after predetermined nonlinear processing is stored in a storage means, And a non-linear signal processing device that can arbitrarily change the characteristics of non-linearization such as gamma correction by appropriately setting a correction rate by which the difference value between the input and output signals is multiplied. I have.

[0005]

However, in the above-mentioned conventional technique, although the gamma characteristic can be arbitrarily changed, the gradation in either the high luminance region or the low luminance region can be expanded. In the case of the observation image in the above, there are a portion that becomes a high-luminance portion and a portion that becomes a low-luminance portion in the screen as described above. It is difficult to do faithfully.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem in an image pickup apparatus provided with a conventional light source device, and always provides a gradation of an image having a high luminance portion or a low luminance portion near the center of the image. It is an object of the present invention to provide a video signal processing device that can be uniformly and effectively spread.

[0007]

According to a first aspect of the present invention, there is provided a video signal processing apparatus in an imaging apparatus for imaging a subject illuminated by illumination light from a light source device. Storage means for generating a coefficient which changes stepwise from the center of the screen of the input video signal toward the periphery of the screen, calculation means for multiplying the coefficient output from the storage means by the input video signal, and output of the calculation means And non-linear processing means for performing non-linear conversion of

In the video signal processing apparatus thus configured, when the center of the screen of the input video signal of one screen has low luminance, the coefficient of the center is set to 1 or more, and the coefficient is gradually increased toward the peripheral part. The coefficient is set to 1 or less in the peripheral portion by making it smaller. When the luminance is high at the center of the screen, the coefficient at the center is set to 1 or less, and the coefficient is increased stepwise toward the periphery, and set to 1 or more at the periphery. Then, the coefficient is stored in a storage unit such as a memory, and is appropriately multiplied by an input video signal corresponding to a screen position, and then nonlinear processing represented by gamma correction is performed. By multiplying by the coefficient set in this way, a high-brightness region where the vicinity of the center of the screen has higher or lower brightness than the peripheral portion due to a unique structure of the subject such as an endoscope image is reduced. Even on a screen in which the luminance areas are mixed, it is possible to display an image without impairing the gradation expression in the high luminance area or the low luminance area peripheral part.

According to a second aspect of the present invention, in the video signal processing apparatus according to the first aspect, means for detecting a luminance signal level at a central portion and a peripheral portion of the screen, and each of the luminances detected by the detecting means. Means for comparing signal levels, wherein the storage means is configured to selectively generate a coefficient in accordance with a result of comparison of the luminance signal levels by the comparing means. In the video signal processing device configured as described above, the luminance signal level at the center of the screen and the average luminance signal level at the peripheral part are detected and compared, respectively, so that the luminance signal level can be adjusted according to the luminance distribution of the subject in the screen. It is possible to automatically select and set a coefficient for setting an optimum gain.

[0010]

Next, an embodiment will be described. FIG. 1 is a schematic diagram showing the overall configuration of an electronic endoscope to which a first embodiment of a video signal processing device according to the present invention has been applied. In FIG. 1, reference numeral 1 denotes an insertion portion of an electronic endoscope, and a solid-state imaging device including an objective lens 2 at a tip of the insertion portion 1 and a charge-coupled device (CCD) at a position where an object image is formed on the objective lens 2. 3 are arranged. Reference numeral 4 denotes an illumination light guide for irradiating the subject with illumination light. The illumination light guide 4 is irradiated with illumination light from a light source lamp 6 disposed in the light source unit 5 through a rotary RGB filter 7 that is driven to rotate at a constant speed by a motor (not shown). Has become.

The video signal processing section 8 is for performing image pickup of a frame sequential method. The pre-processing circuit 10 and the CCD drive circuit 11 are connected to the solid-state image pickup Connected to element 3. The control signal generation circuit 12 controls the generated timing signal,
The signal is supplied to each circuit section. The CCD drive circuit 11
A drive signal for driving the solid-state imaging device 3 is generated by a signal from the control signal generation circuit 12.

Video signal data output from the solid-state imaging device 3 driven by the CCD drive circuit 11 is input to a pre-processing circuit 10 and subjected to processing such as amplification and waveform shaping. Is converted into digital data. The video signal converted to digital data is subjected to multiplication by a coefficient, which will be described later with reference to FIG. The synchronized video data is subjected to display control such as switching between a moving image and a still image in a memory circuit 16, and then converted into an analog signal in a digital-to-analog converter 17.
The video of the subject is reproduced on the monitor 19 via the.

FIG. 2 is a block diagram showing the internal configuration of the gamma conversion circuit 14 in FIG. In FIG. 2, reference numeral 21 denotes a control circuit for generating an address of an LUT (lookup table), 22 denotes an LUT, 23 denotes a multiplier,
24 is a clip circuit, and 25 is a gamma correction circuit. The control circuit 21 receives the signal from the control signal generation circuit 12, and outputs the horizontal and vertical positions of the currently input video signal as an address. This address is input to an LUT 22 represented by a ROM. This LUT
From 22, coefficients depending on the position of the screen are output as data. The coefficient is multiplied by the video signal, and after passing through the clipping circuit 24, the gamma correction circuit 25 performs gamma correction.

Next, the operation of the first embodiment configured as described above will be described. The coefficient (data) for the screen position (address) is stored in the LUT 22 in the gamma conversion circuit 14, and outputs the coefficient at each position on the screen according to the scanning direction of the pixel. The address relating to the position of the coefficient is input from the control circuit 21 and is converted into a coefficient by the LUT 22 for each position. This coefficient is set so as to change stepwise from the center of the screen toward the peripheral portion as shown in FIG. In this example, it is assumed that the central part 101 of the screen is dark and the peripheral part 102 is a bright tubular object, and the central part 101 of the screen is 1 (256/256).
As described above, the coefficient table for setting the screen peripheral portion 102 to 1 (256/256) or less is set. Next, the coefficient set in the LUT 22 and the video signal are multiplied by the multiplier 23, and the clipping circuit 24 clips the overflow. Thereafter, the gamma correction circuit 25 performs non-linear conversion processing represented by gamma correction on the output video signal of the clip circuit 24.

By performing signal processing in the gamma conversion circuit 14 as described above, in a scene in which a tubular subject is imaged, if illumination light is not sufficiently applied to the center of the screen, the gain is increased in a low-luminance area in the center. In this way, it is possible to display a wide range of gradations, and in a high luminance region in the periphery, it is possible to secure a luminance that can maintain observation without compressing the gradation by suppressing an increase in gain. Also, in a normal subject, when it is desired to highlight the central portion, the same distribution coefficient can be used. On the other hand, when the luminance at the center of the screen is high, contrary to the coefficient distribution of FIG. 3, a coefficient table for setting the center of the screen to 1 or less and the periphery of the screen to 1 or more can be selectively used. is there.

Next, a video signal processing apparatus according to a second embodiment of the present invention will be described. FIG. 4 is a block diagram showing a configuration of a gamma conversion circuit which is a main part of the second embodiment. The configuration other than this gamma conversion circuit is the same as that of the first embodiment shown in FIG. . In FIG. 4, the same components as those of the gamma conversion circuit of the first embodiment shown in FIG. 2 are denoted by the same reference numerals, and description thereof will be omitted. In FIG. 4, reference numeral 26 denotes a detection circuit for detecting the luminance level at the center of the screen, 27 denotes a detection circuit for averaging and detecting the luminance level at the periphery of the screen, and 28 denotes a luminance detection circuit for the center.
This is a comparison circuit that compares the luminance level of 26 with the luminance level of the peripheral luminance detection circuit 27.

FIG. 5 shows portions A to E for detecting luminance on the screen. In the present embodiment, the luminance of the central portion E is detected by the central luminance detecting circuit 26, and the average value of the luminance of the four peripheral portions (A, B, C, D) is detected by the peripheral luminance detecting circuit 27. Detected. The luminance level e output from the central luminance detecting circuit 26 and the average luminance level (a + b + c + d) / 4 output from the peripheral luminance detecting circuit 27 are compared by a comparing circuit 28. When the average value (a + b + c + d) / 4 of the parts A to D is lower and higher than the average value (a + b + c + d) / 4, the coefficient characteristics as shown in FIGS. 6A and 6B and FIGS. 7A and 7B respectively. Correction is performed using the LUT 22. The horizontal axes of FIGS. 6A and 6B and FIGS. 7A and 7B are XX ′ of the screen shown in FIG.
The vertical axis corresponds to the multiplication coefficient at that screen position, corresponding to the position along the line and the line YY '. If there is no large difference in the result of the comparison of the brightness levels, the correction by the LUT 22 may not be performed. In addition, for the display effect, there is no problem even if the characteristics shown in FIGS. 6A and 6B and the characteristics shown in FIGS. 7A and 7B are reversed. In the examples shown in FIGS. 6A and 6B, the coefficient characteristic crosses the luminance level 1.0. Of course, the coefficient for all positions on the screen is set to 1.0 or more and 1.0 or less. In some cases, you may not cross level 1.0.

As described above, in the second embodiment,
The luminance distribution of the subject in the screen is detected according to the shape of the subject, and the correction coefficient can be automatically selected and set from the detection result.

In each of the above embodiments, the present invention is applied to a frame sequential type electronic endoscope provided with a light source device. However, the present invention uses a unique light source such as a simultaneous type electronic endoscope. The present invention can also be applied to a video signal processing device of an imaging device that uses and captures an image.

[0020]

As described above based on the embodiment, according to the first aspect of the present invention, the vicinity of the center of the screen is higher than that of the peripheral part due to the unique structure of the subject such as an endoscope image. Even on a screen in which a high-luminance area and a low-luminance area are mixed such that the luminance or the low-luminance is present, it is possible to display an image without impairing the gradation expression of the high-luminance area or the low-luminance area peripheral portion. Become. According to the second aspect of the present invention, the coefficient is selectively generated in accordance with the comparison result between the luminance signal level at the center of the screen and the average luminance signal level at the peripheral part. A coefficient for setting an optimum gain according to the luminance distribution of the subject can be automatically selected and set.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating an overall configuration of an electronic endoscope to which a first embodiment of a video signal processing device according to the present invention has been applied.

FIG. 2 is a block diagram showing a configuration of a gamma conversion circuit according to the first embodiment shown in FIG.

FIG. 3 is a diagram showing coefficients set in an LUT corresponding to a tubular subject.

FIG. 4 is a block diagram illustrating a configuration of a gamma conversion circuit according to a second embodiment of the present invention.

FIG. 5 is a diagram showing a portion for detecting screen brightness in the second embodiment.

FIG. 6 is a diagram illustrating coefficient characteristics when a luminance level in a central portion is lower than an average luminance level in a peripheral portion.

FIG. 7 is a diagram illustrating coefficient characteristics when the luminance level at the center is higher than the average luminance level at the periphery.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electronic endoscope insertion part 2 Objective lens 3 Solid-state image sensor 4 Lighting guide 5 Light source part 6 Light source lamp 7 Rotating RGB filter 8 Video signal processing part 9, 18 Connector 10 Pre-processing circuit 11 CCD drive circuit 12 Control signal generation Circuit 13 Analog to digital converter 14 Gamma conversion circuit 15 Synchronization circuit 16 Memory circuit 17 Digital to analog converter 19 Monitor 21 Control circuit 22 LUT 23 Multiplier 24 Clip circuit 25 Gamma correction circuit 26 Central luminance detection circuit 27 Peripheral luminance detection Circuit 28 Comparison circuit

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4C061 CC06 LL02 MM03 NN01 SS08 SS10 SS11 SS23 TT01 TT06 TT20 5B057 AA07 BA02 CA01 CA08 CA12 CA16 CB01 CB08 CB12 CB16 CC01 CE11 CH07 5C021 PA17 PA85 PA86 RB03 XA32 A33 CA04 CC07 EA01 EA05 EB05 EB07 ED13 HA12

Claims (2)

[Claims] An image signal processing apparatus in an image pickup apparatus for picking up an image of a subject illuminated by illumination light from a light source device, wherein a coefficient of an input image signal of one screen changes stepwise from the center to the periphery of the screen. Video signal processing comprising: storage means for generating; arithmetic means for multiplying a coefficient output from the storage means with an input video signal; and non-linear processing means for non-linearly converting the output of the arithmetic means. apparatus. 2. The apparatus according to claim 1, further comprising: means for detecting a luminance signal level at a central portion and a peripheral portion of the screen; and means for comparing respective luminance signal levels detected by the detecting means. 2. The video signal processing device according to claim 1, wherein the video signal processing device is configured to selectively generate a coefficient in accordance with a result of the comparison of the luminance signal levels according to the above.