JP3267200B2 - Image processing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus, and more particularly, to a gamma correction process for a video signal in a backlight state.

[0002]

2. Description of the Related Art In recent years, many backlight correcting means have been developed for an image processing apparatus.
There is a gamma correction device disclosed in Japanese Patent Application Laid-Open No. 2 (1994). Hereinafter, the conventional gamma correction device will be described.

FIG. 11 is a block diagram of a conventional gamma correction circuit. In FIG. 11, reference numeral 1101 denotes an imaging apparatus; 1102, a gain control circuit whose gain changes according to a voltage; 1103, an attenuation control circuit whose attenuation in a required level range changes according to a voltage; Reference numeral 1105 denotes an average value detecting means, and reference numeral 1106 denotes a gain control data ROM. The operation will be described below.

[0006] The video signal obtained by the image pickup device 1101 is divided into predetermined level ranges by a level range dividing means 1104, and an average value or integrated value for each level range is detected by an average value detecting means 1105. Gain control data ROM 11
In 06, a gain or an attenuation amount according to an average value or an integral value of each of these level ranges is set, and a gain control circuit 1102 performs gamma correction of a video signal in accordance with an output signal of the gain control data ROM. This is performed in the circuit 1103.

[0005]

As described above, in the conventional gamma correction processing in an image processing apparatus in a backlight state, the gain for each level is controlled by a gradation distribution for each predetermined level range. When the subject is wearing black clothes in the light state, the distribution of low gradations increases as shown in FIG. 7, so the gain of the low gradation part increases, and despite the fact that the subject is in the normal light state, The same processing as in the backlight state correction is performed, and there is a problem that an image is overexposed.
Further, even when the background of the subject is a dark wall, there is a problem that the gamma correction cannot be performed accurately due to the distribution characteristics of the wall.

An image in the backlight state contains more noise components than an image in the normal light state. However, since the low luminance portion contains more noise components, the noise becomes more noticeable with the correction of the backlight state. At first, there is a problem that noise is further emphasized by the outline emphasis processing performed to sharpen an image, and the image quality is reduced. Further, with the correction of the backlight state, the brightness of the low-luminance portion is improved, but the gradation disappears. On the contrary, the gradation skip occurs in the low-luminance portion as shown in the luminance histogram of FIG. There is a problem that a false contour appears in an image, and a problem that image quality is deteriorated because the false contour is enhanced by the contour enhancement processing.

Further, the image from the CCD contains a color noise component such as a false color, and the luminance of the image is increased by the correction of the backlight state by the gamma correction. There is a problem that the color noise becomes noticeable due to the correction.

[0008]

In order to solve the above-mentioned problems, an image processing apparatus according to the present invention comprises: means for creating a histogram indicating a gradation distribution characteristic from an input video signal; and a predetermined histogram based on the created histogram. And a means for calculating a gamma correction amount according to the size of the peak pattern.

According to the present invention, the amount of gamma correction is determined based on the peak pattern of a high-luminance portion generated at the time of backlight.
The gamma correction amount can be accurately determined regardless of what kind of clothes the subject wears or the background. In addition, since the amount of edge enhancement is suppressed and the color noise component is removed based on the size of the peak pattern, it is possible to prevent a decrease in image quality due to gamma correction.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An image processing apparatus according to a first aspect of the present invention comprises: means for creating a histogram indicating gradation distribution characteristics from an input video signal;
The maximum value of the distribution number of the predetermined high-luminance part and this high luminance
And means for calculating a gamma correction amount according to the magnitude of the detected peak value. This has the effect that the gamma correction amount can be accurately determined regardless of the kind of clothes and the background.

Next, an image processing apparatus according to a second aspect of the present invention provides a means for creating a histogram indicating gradation distribution characteristics from an input video signal, and a predetermined histogram based on the created histogram.
The maximum number of distributions in the high-luminance area and the
Means for detecting the peak value calculated by the difference from the average value , and comprising a contour emphasis means for controlling the amount of contour emphasis according to the magnitude of the detected peak value , This has the effect of not emphasizing noise and false contours generated by gamma correction.

Next, an image processing apparatus according to a third aspect of the present invention provides a means for creating a histogram showing gradation distribution characteristics from an input video signal, and a predetermined histogram based on the created histogram.
The maximum number of distributions in the high-luminance area and the
Means for detecting a peak value calculated from a difference from the average value, and color difference correction amount calculating means for controlling a low-pass filter process on a color difference signal according to the magnitude of the detected peak value.
This has the effect that it is possible to suppress the color noise that increases in luminance with gamma correction and starts to stand out.

[0013]

(Embodiment 1) The first aspect of the present invention will be described below.
An embodiment of the invention described in claim 4 will be described with reference to the drawings.

FIG. 1 is a block diagram of an image processing apparatus showing the basic configuration of the present invention. In FIG. 1, reference numeral 101 denotes a histogram creating circuit for creating a histogram indicating a gradation distribution from the luminance signal Y, and 102 denotes a peak value for quantifying the magnitude of the peak value of the peak pattern of the high luminance portion from the created histogram. A detection circuit 103 determines a gamma correction amount based on the magnitude of the peak value and performs a gradation correction, and a gradation correction circuit 104 performs a contour enhancement.
5 is a contour emphasis amount calculation circuit that determines the contour emphasis amount according to the magnitude of the peak value, and 106 is
A color difference correction amount calculation circuit 107 that determines the strength of the low pass filter applied to the color difference signal, and a low pass filter 107 that performs low pass filtering on the color difference signal based on the correction coefficient.

FIG. 2 shows a histogram generating circuit 10 in FIG.
FIG. 1 is a diagram illustrating an example of an extracted luminance histogram. In this case, a peak pattern portion a is present in a high luminance portion, and the histogram in a backlight state is shown. FIG. 3 is a block diagram of the peak value detection circuit 102 in FIG. 1, wherein 301 is a comparator, 302 is a pixel counter, 303 is a maximum distribution number detection circuit, 304 is a distribution average value calculation circuit, and 305 is a subtractor. is there.

FIG. 4 is a gradation correction characteristic diagram of the gradation correction circuit 103 in FIG. 1, and FIG. 5 is a contour enhancement circuit 104 in FIG.
501 is a block diagram of a contour component extraction circuit;
Reference numeral 2 denotes a noise coring processing circuit for removing noise components in a level, 503 denotes an adder, and 504 denotes a delay circuit.
FIG. 6 is an explanatory diagram of the low-pass filter 107 in FIG.

The operation of the image processing apparatus configured as described above will be described below. First, input data is assumed to be 8-bit data. That is, in the luminance signal, 0 is black data and 255 is white data. In FIG. 1, a histogram is created by a histogram creating circuit 101 from an input luminance signal Y.

FIG. 2 shows a histogram of the input signal Y created by the histogram creating circuit 101. In particular, in this case, since there is a peak portion on the high brightness side as indicated by a, it can be determined that the brightness distribution is in a backlight state. . Figure 2 in backlight
Since a peak pattern appears on the high luminance side as shown by a in the figure, the amount of gamma correction is determined by digitizing this peak pattern. That is, if the peak value is large, it is determined that the backlight state is strong, the gamma correction amount is increased according to the magnitude of the peak value, and if the peak value is small, it is determined that the backlight state is weak, and the gamma correction amount is reduced. I do.
If there is no peak value on the high luminance side, it is determined that the subject is not in a backlight state, and no gamma correction is performed. According to this method, for example, in a case where black clothes or the like are worn in a normal light state, a histogram as shown in FIG. 7 is obtained. However, since there is no peak pattern, it is determined that the object is not in a backlight state, so that a malfunction can be prevented.

The digitization of the peak pattern is performed by the difference between the maximum value and the average value of the distribution of the high luminance portion. This is performed by the peak value detection circuit 102. Peak value detection circuit 1
As shown in FIG. 3, first, only the luminance distribution of the high luminance portion is extracted by the comparator 301, the number of distributions for each luminance is counted by the counter 302, and the maximum distribution number detection circuit 3
At 03, the maximum number of distributions at the maximum value of the peak pattern is calculated, and the distribution average value calculation circuit 304 measures the average value of the distribution of a predetermined high luminance portion. For example, the luminance at which the signal level is 200 or higher is defined as high luminance, and the maximum number of distributions at the maximum value of the number of distributions in the histogram from 200 to 255 and the average value of the distribution from 200 to 255 are obtained. Next, the difference between the maximum number of distributions and the average value is determined, and the peak value indicating the size of the peak pattern is determined. By using the peak value calculated in this way as the intensity of the backlight state, for example, even when the subject is wearing black clothes or white clothes in the normal light state, accurate correction can be performed. .

Next, a gradation correction amount, that is, a gamma correction amount is determined as shown in FIG. 4 based on the magnitude of the peak value calculated as described above. For example, the relationship between input data and output data is (output data) = (input data) × γ, and if the peak value is large, the correction amount is increased as shown by the curve A in FIG. 4 and the peak value is small. For example, when the gamma correction amount is set to a small value as indicated by B in FIG.
Correction is not performed as in C in FIG. The association between the peak value and the value of γ is performed, for example, as shown in FIG. That is, when the peak value is zero, no correction is performed with γ = 1, and the luminance correction amount is increased as the peak value increases, and when the peak value is larger than a certain value, a limiter is used to avoid excessive correction. To be applied. In this case, the value of γ is limited to 0.3. Further, as shown in D of FIG. 4, instead of an exponential function, the gamma correction amount may be determined by determining the knee point K and the white clip point W according to the peak value. . In this case, if the peak value is large, the values of the knee point K and the white clip point W are increased,
Gamma correction is performed using a conversion equation interpolated by a straight line. In this method, overexposure and the like due to gamma correction can be suppressed.

When the peak value is large, a process for suppressing the contour enhancement of luminance is performed. This is because, when the luminance component is gradation-corrected by gamma correction, the gradation of the low-luminance part disappears instead of improving the brightness of the low-luminance part, and the gradation skip occurs at the low luminance as shown in FIG. This is because false contours appear and noise originally present in the low gradation part starts to be noticeable due to an increase in luminance. If contour enhancement is performed as it is, noise will be enhanced. Therefore, when the peak value is large, a signal for suppressing the contour enhancement amount of the luminance is generated from the contour enhancement amount calculation circuit 105, and the contour enhancement circuit 104 suppresses the contour enhancement amount based on the signal. Perform processing. FIG. 5 is a block diagram showing the contour emphasizing circuit 104, which includes a contour component extracting circuit 501, a noise coring processing circuit 502, an adder 503, and a delay circuit 504. In FIG. 5, a contour component extraction circuit 501
Then, the difference between the target pixel data and the upper, lower, left, and right pixel data is calculated. That is, contour component = (target pixel data) − (upper pixel data) + (target pixel data) − (lower pixel data) + (target pixel data) − (left pixel data) + (target pixel data) − (right pixel Data) = (target pixel data) × 4- (upper pixel data) − (lower pixel data) − (left pixel data) − (right pixel data), and an outline component is extracted. This contour component is not added to the original data as it is by the adder 503, but the tone correction circuit 103 is added by the noise coring processing circuit 502.
The noise such as the false contour component generated by the correction is not added. That is, the noise coring processing circuit 502 does not add the contour components from the level -X to the level X to the original data so as not to emphasize the noise, thereby preventing the image quality from lowering. The contour emphasis amount calculation circuit 105 outputs the level X value to the contour emphasis circuit 104 when the peak value is large, and outputs a large value when the peak value is small. For example, as shown in FIG. 10, by associating the magnitude of the peak value with the value of the level X, it is possible to prevent the noise component generated by the gamma correction amount from being emphasized.

Next, when the peak value is large, the color difference signal is subjected to a low-pass filter to suppress color noise. This is C
When photographed in a backlight state on a CD, the image has color noise components, but the color noise is not so noticeable because the image is dark. However, since the brightness is improved by the gamma correction, color noise starts to stand out. Therefore, color noise is suppressed by the magnitude of the peak value. FIG. 6A shows an array of input pixel data, and FIG. 6B shows processed data. When the peak value is large, the averaging process is performed with 9 data of the target pixel P5 and its surrounding pixels. That is, output data Q = (P1 + P2 +
If the peak value is not so large, the averaging process Q = (P4 + P5 + P6) / 3 is performed on the three data of the target pixel and the left and right pixels. If there is no peak, the averaging process is not performed. As described above, by reducing the color noise by the magnitude of the peak value, it is possible to prevent the image quality from lowering.

[0024]

As described above, according to the image processing apparatus of the present invention, the peak value is calculated from the peak pattern of the high-luminance portion generated at the time of backlight, and the gamma correction amount is determined based on the peak value. The gamma correction amount can be accurately determined regardless of what clothes are worn and the background. In addition, since the amount of edge enhancement is suppressed and the color noise component is removed based on the magnitude of the peak value, it is possible to prevent a decrease in image quality due to gamma correction.

[Brief description of the drawings]

FIG. 1 is an overall block diagram of an image processing apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a luminance histogram according to the embodiment of the present invention.

FIG. 3 is a block diagram of a peak value detection circuit according to the embodiment of the present invention.

FIG. 4 is a gradation correction characteristic diagram according to the embodiment of the present invention.

FIG. 5 is a block diagram of an outline emphasis circuit according to the embodiment of the present invention;

FIG. 6 is an explanatory diagram of a low-pass filter according to the embodiment of the present invention.

FIG. 7 is a diagram showing a histogram in the case of a normal light state according to the embodiment of the present invention.

FIG. 8 is a correspondence diagram between a peak value and a gamma correction amount in the embodiment of the present invention.

FIG. 9 is a diagram showing a histogram showing a gradation skip state according to the embodiment of the present invention.

FIG. 10 is a characteristic diagram of a contour emphasis amount calculation circuit according to the embodiment of the present invention;

FIG. 11 is a block diagram of an image processing apparatus according to a conventional embodiment.

[Explanation of symbols]

 Reference Signs List 101 histogram creation circuit 102 peak value detection circuit 103 gradation correction circuit 104 contour enhancement circuit 105 contour enhancement amount calculation circuit 106 color difference correction amount calculation circuit 107 low-pass filter 301 comparator 302 counter 303 maximum distribution number detection circuit 304 distribution average value calculation circuit 305 Subtractor 501 Contour component extraction circuit 502 Noise coring processing circuit 503 Adder 504 Delay circuit 1101 Image pickup device 1102 Gain control circuit 1103 Attenuation control device 1104 Level range division means 1105 Average value detection means 1106 Gain control data ROM

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-7-23287 (JP, A) JP-A-9-51472 (JP, A) JP-A-7-162717 (JP, A) JP-A 8- 65543 (JP, A) JP-A-6-30330 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04N 5/14-5/217 H04N 9/64

Claims (3)

(57) [Claims] 1. A means for creating a histogram indicating a gradation distribution characteristic from an input video signal, and a predetermined maximum number of distributions of a high-luminance portion from the created histogram,
An image processing apparatus comprising: means for detecting a peak value calculated based on a difference from an average value of a distribution of luminance portions; and means for calculating a gamma correction amount according to the magnitude of the detected peak value . 2. A means for creating a histogram indicating a gradation distribution characteristic from an input video signal, and a predetermined maximum value of the number of distributions of a high-luminance portion based on the created histogram.
It is characterized in that it comprises means for detecting a peak value calculated from a difference from the average value of the distribution of the luminance portion, and contour emphasis means for controlling the amount of contour emphasis according to the magnitude of the detected peak value. An image processing apparatus. 3. A means for creating a histogram indicating a gradation distribution characteristic from an input video signal, and a predetermined maximum value of the number of distributions of a high-luminance portion based on the created histogram.
Means for detecting a peak value calculated from the difference from the average value of the distribution of the luminance portion, and color difference correction for controlling a low-pass filter process on the color difference signal according to the magnitude of the detected peak value.
An image processing apparatus comprising an amount calculating unit .