JPH07143357A - Color image pickup device - Google Patents

Abstract

PURPOSE:To automatically set a compression ratio and a knee point to an optimum value in a knee correcting circuit. CONSTITUTION:A signal of the maximum level in three primary color signals from an image pickup element is detected by an NAM circuit 21. The peak level of the maximum level signal in the three primary colors signals detected by the NAM circuit 21 is detected by a peak detecting circuit 23. Knee correcting circuits 11R, 11G and 11B compress a video signal of a high luminance part exceeding a prescribed polygonal point level by a prescribed compression ratio and compress the video signal within a prescribed signal level, and also, the polygonal point level can be varied and set, and moreover, the compression ratio can be varied and set. In accordance with the peak level detected by the peak detecting circuit 23, the polygonal point level of the knee correcting circuit 11R, 11G and 11B is set. The compression ratio of a knee correction is set from a signal level standard of an input signal of the knee correcting circuits 11R, 11G and 11B, a white clip level, and the minimum polygonal point level of the knee correcting circuits 11R, 11G and 11B.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image pickup device, and more particularly to a circuit portion for compressing a high brightness level portion.

[0002]

2. Description of the Related Art Although the dynamic range of a signal obtained from an image pickup device is relatively wide, the image pickup device cannot transmit and output all of this signal. Therefore, in the image pickup apparatus, the video signal processing circuit compresses the video signal within a specified level.

A circuit for compressing the video signal is called a knee correction circuit and has an input / output characteristic as shown in FIG. That is, the dynamic range of the signal obtained from the image pickup device is set to, for example, about 600%, but the output of the image pickup apparatus is compressed to a maximum of about 110% (this becomes the white clip level).

As shown in the figure, the knee correction circuit operates so that when the amount of incident light is below a predetermined level, signal compression is not performed between its input and output, but when it exceeds a predetermined level, signal compression is performed. . The branch point (bending point of the characteristic) P of whether or not to perform signal compression is the breaking point level (knee point).
is called.

The knee correction processing includes a manual knee correction mode and an automatic knee correction mode. In the case of the manual knee correction mode, fixed values of the knee point and the compression ratio (corresponding to the inclination of the portion beyond the knee point in the above input / output characteristic diagram) are set. FIG. 6 shows an example of characteristics in the manual correction mode.

On the other hand, in the auto knee correction mode,
The maximum value of the three primary color signals of red (R), green (G), and blue (B) is extracted, and the maximum value is supplied to the peak detection circuit to extract the peak value of the video signal in the screen. Then, the signal is compressed so that this peak value converges to a specified level (white clip level).

Therefore, in the auto knee correction mode, a predetermined compression ratio (knee slope) is set in the knee correction circuit, and the peak level is detected by the white clip circuit according to the peak level detected by the peak detection circuit. As shown in FIG. 7, the knee point is variably set to the calculated value so as not to be clipped. That is, in the auto knee correction mode, the knee point changes according to the fluctuation of the peak level of the input signal, and the peak value of the output signal of the knee correction circuit converges to the white clip level or less. In FIG. 7, NAM indicates the detected value of the maximum peak value of the three primary color signals.

[0008]

By the way, in the above auto knee correction mode, how to determine the compression ratio and the knee point in consideration of the relationship between them is a problem, and it is quite appropriate to set them appropriately. Was difficult.

For example, in consideration of increasing the contrast in the high brightness level portion, the compression ratio in the knee correction circuit should be small. However, when the compression ratio is small, the break point level (knee point) must be set low as shown in FIG. 8, and the parts other than the high-luminance part are also compressed, and the contrast is reduced. Will fall.

As shown in FIG. 9, when the compression ratio is changed without changing the knee point and the compression ratio is smaller than an appropriate value, the peak level of the video signal is clipped. On the contrary, when the compression ratio is larger than the appropriate value, the signal level does not reach the white clip level. Therefore, when the compression ratio is changed, the knee point must also be changed, but as shown in FIGS. 10A and 10B, the rate of change in the break point level (knee point) must be set according to the compression ratio. However, the above-mentioned state will occur.

A first object of the present invention is to appropriately set a compression ratio and a knee point so that compression of a portion other than a high luminance portion can be minimized and contrast of a high luminance portion can be increased. It is to be able to do.

In the conventional auto knee correction mode, the peak level detected by the peak detection circuit is accurately detected even if the area of the high brightness level portion is small,
Set the knee point of the knee correction circuit to operate so that the peak level is not clipped.

Therefore, conventionally, even if the brightness is high on the screen, it is easily affected by an unnecessary subject, such as a spotlight or a fluorescent lamp, and a necessary subject portion is unnecessarily compressed. However, there is a drawback that the contrast in that part becomes small.

A second object of the present invention is, in view of the above points, to prevent a necessary object portion from being unnecessarily compressed.

[0015]

In order to achieve the first object, the color image pickup apparatus according to the present invention includes an image pickup element 1 and an image pickup element 1 corresponding to the reference numerals of the embodiments described later. Means 21 for detecting the maximum level signal of the three primary color signals, peak detection circuit 23 for detecting the peak level of the maximum level signal of the three primary color signals, and a high brightness portion above a predetermined break point level Is a knee correction circuit capable of variably setting the break point level and variably setting the compression ratio. 11R, 11G, 11B and the peak detection circuit 23
Means 24 for setting the break point level of the knee correction circuits 11R, 11G, and 11B according to the peak level detected by the above, the signal level standard of the input signal of the knee correction circuits 11R, 11G, and 11B, and white clipping And a means 24 for setting the compression ratio of the knee correction circuit based on the level and the minimum break point level of the knee correction circuit.

Further, in order to achieve the second object, the image pickup device 1, means 21 for detecting a signal of the maximum level among the three primary color signals from the image pickup device 1, and among the three primary color signals are provided. A peak detection circuit 23 for detecting the peak level of the maximum level signal, and a circuit for compressing a video signal of a high brightness portion above a predetermined break point level with a predetermined compression ratio to compress the video signal within a specified signal level. Yes, the knee correction circuits 11R and 11G whose fold level can be variably set,
11B and the break level 11 of the knee correction circuit according to the peak level detected by the peak detection circuit 23.
A low-pass filter 22 is provided between the means 24 for setting R, 11G, and 11B, the means 21 for detecting the maximum level signal of the three primary color signals, and the peak detection means 23.

[0017]

In the present invention having the above construction, the compression ratio for knee correction is dynamically set from the input signal of the knee correction circuit, the white clip level, and the minimum break point level, so that it is always appropriate. Knee correction can be performed.

Further, by providing the low-pass filter 22 between the means for detecting the maximum level signal of the three primary color signals and the peak detection circuit, even if the brightness is high, the area is small and unnecessary. It is possible to prevent a necessary subject from being compressed due to the influence of the subject.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a color image pickup apparatus according to the present invention will be described below with reference to the drawings. FIG. 1 is a first half of the block diagram and FIG. 2 is a continuation of the block diagram.

In FIG. 1, reference numeral 1 denotes an optical system including an image pickup lens, a spectral prism, and the like. In this optical system 1, the light incident from the lens is transmitted by a prism or the like.
After being decomposed into red (R), green (G), and blue (B) light, they are incident on the CCD image pickup devices 2R, 2G, and 2B for the respective primary colors, and the red, green, and blue electric signals are generated. Primary color signal SR,
Converted to SG, SB.

The three primary color signals SR, SG and SB from the image pickup devices 2R, 2G and 2B are respectively supplied to the CDS (correlated double sampling) circuits 3R, 3G and 3B and the trap filters 4R, 4G and 4B at the subsequent stage. , Image sensor 2
The peculiar clock component superposed on the output signals of R, 2G and 2B is removed. Trap filter 4R, 4
The three primary color signals from G and 4B are supplied to amplifiers 5R, 5G and 5B.
And the sensitivity is adjusted.

The three primary color signals from the amplifiers 5R, 5G and 5B are supplied to the analog signal processing circuits 6R, 6G and 6B and subjected to analog processing such as shading correction, gain up and clamp. The three primary color signals from the analog processing circuits 6R, 6G and 6B are supplied to the prinny circuits 7R, 7G and 7B.

In the case of this example, the prinny circuits 7R and 7R
The compression ratios of G and 7B are changed to 1/4 and 1/5 in the manual knee mode and the auto knee mode, respectively, and the knee point is changed by the control signal from the system control circuit 24 described later. Can be changed. The compression here is performed corresponding to the dynamic range of A / D converters 9R, 9G, 9B described later.

The high-frequency components of the outputs of the prinny circuits 7R, 7G, 7B are removed by the low-pass filters 8R, 8G, 8B, and then the A / D converter 9R,
It is supplied to 9G and 9B, respectively, and is converted into, for example, a 10-bit digital signal. This A / D converter 9
The three primary color signals converted into digital signals from R, 9G and 9B are digital signal processing circuits 10R, 10G and 10
B is supplied to B, and NAM (Non Addiv
e Mix) circuit 21.

In the digital signal processing circuits 10R, 10G and 10B, processings such as linear matrix processing, detail signal addition, gamma correction, flare correction and pedestal addition are performed.

The gamma correction is performed by mixing the gamma correction signal approximated by the polygonal line with the input signal. The gamma correction signal level is set by the system control circuit 24.
It is variable by.

This digital signal processing circuit 10R, 10G
The digital signals of the primary color signals from 10 and 10B are supplied to knee correction circuits 11R, 11G and 11B. In the knee correction circuits 11R, 11G, and 11B, the compression ratio and knee point are set by the system control circuit 24 as described later, and the level of the high-luminance portion is compressed.

The knee correction circuits 11R, 11G and 11
The primary color signal of the digital signal from B is supplied to the white clip circuits 12R, 12G and 12B, respectively, where white clip processing is performed, and the NTSC encoder 1
3 and encoded into an NTSC signal. The NTSC signal from the encoder 13 is converted into an analog signal by the D / A converter 14, and the low pass filter 1
In step 5, unnecessary high frequency components are removed and output terminal 16
And output to, for example, a VTR or monitor receiver.

On the other hand, the NAM circuit 21 outputs the maximum value of the digital signals of the three primary color signals inputted thereto. The output signal of the NAM circuit 21 is supplied to the peak detection circuit 23 via the low-pass filter 22, and the peak level in one field is detected. Then, the peak level is supplied to the system control circuit 24.

The low-pass filter 22 reduces the peak level in a portion of the screen having high brightness but a small area in accordance with the area. As a result, if the area is not large to a certain extent, the output signal of the NAM circuit 21 will be detected by the peak detection circuit 23 so that its peak level is small, which is necessary for an unnecessary object having a small area even with high brightness. The subject will not be compressed.

The system control circuit 24 obtains a compression ratio (knee slope) as described later and sets it in the knee correction circuits 11R, 11G and 11B, and within one field from the peak detection circuit 23. The knee point is calculated according to the peak level of and the knee correction circuits 11R, 11G and 11B are set. The parameter relating to this set value is registered in the system control circuit 24 in advance or sent from a remote controller (not shown).

[About Auto Knee Correction] In the auto knee correction of this example, the knee correction point (knee point) is adjusted in accordance with the change in the detected peak value of the peak detection circuit 23 described above to reach a predetermined dynamic range. It realizes the function to output at the maximum compression rate without applying clips. Therefore, the video signal is output in the state where the dynamic range and the contrast are the best for any subject.

In the case of this example, the set value can be set instantaneously and discontinuously. Knee points and compression ratios (knee slopes) are important items to be set in this auto knee correction. The setting of the knee slope is obtained from each setting condition, and the knee point is obtained from the peak value from the peak detection circuit 23.

The setting conditions necessary for setting the knee slope and knee point are as follows. The dynamic range, that is, the maximum incident light amount is determined. When the maximum amount of light is determined by the dynamic range of the minimum knee point (when the video signal input to the knee correction circuit is at the maximum level in the standard)
Decide how many points you will have. Since there is a portion where compression is not preferable under any circumstances, the level of this portion is defined as the minimum level of the knee point of the knee correction circuit. White clip level This white clip level is set independently of the auto knee correction operation. For example, 110% and 107% are set. Output peak value of peak detection circuit 23 This peak value is detected for each field and the knee point is set to an appropriate value. However, in this example, since the detection is performed before the pedestal addition circuit and the gamma correction circuit, the inputs of the knee correction circuits 11R, 11G, and 11B are considered in consideration of how the peak value changes in these two circuits. It is necessary to find the peak value at. Pedestal addition + flare correction Set the auto knee correction operation by referring to the value set in the actual pedestal addition circuit. Gamma correction The settings related to the auto knee correction operation are a gamma correction gain and a gamma correction table when the gamma correction is performed by, for example, polygonal line approximation.

As a procedure, the knee slope is calculated from the above set conditions. The knee slope is obtained from the auto knee correction operation when the maximum amount of light is incident. Since the knee point becomes the minimum point when the maximum amount of light is incident, if the white clip level is known, it can be obtained from FIG.

That is, WCP = (MAX-KPmin) × (1 / KS) + KPmin ... (a) 1 / KS = (WCP-KPmin) / (MAX-KPmin) where WCP is the white clip level and MAX is the maximum. The maximum peak level of the inputs of the knee correction circuits 11R to 11B when the amount of light is incident (the video signal input to the knee correction circuits 11R to 11B is the standard maximum level), KPmin is the minimum level of the knee point of the knee correction circuit, and KS is the knee level. It is the compression ratio (knee slope) of the correction circuit.

The above MAX is a pliny point, A / D
It is calculated from the converter output level standard, pedestal addition, and gamma correction circuit settings.

As described above, if the compression ratio KS is set,
From FIG. 3, the peak level is not clipped, and conversely the level does not reach the white clip level.

After the compression ratio is set as described above, the knee point may be set from the peak level detected by the peak detection circuit 23. Here, assuming that the digital signal processing circuits 10R, 10G, and 10B have no fluctuations in the peak level (actually, the environment is such that fluctuations can be calculated), the peak level detected by the peak detection circuit 23 is knee-corrected. The knee point may be set in the circuits 11R to 11B so as to be equal to the white clip level.

WCP = (PEAK-KP) × (1 / KS) + KP (b) PEAK: peak level detected by the peak detection circuit 23 KP: knee point Here, the above equation (a) and (b) are used. From the formula, the following relationship is obtained.

(MAX-KPmin) × (1 / KS) + KPmin = (PEAK-KP) × (1 / KS) + KP KP = (MAX-PEAK) × (1 / (KS-1)) + KPmin ... (c) That is, the output peak level of the peak detection circuit 23 is
If the break point level (knee point) is obtained by substituting it into PEAK in the above equation (c) and set in the knee correction circuit, the peak level output from the knee correction circuit is always equal to the white clip level.

In this case, the knee correction circuits 11R, 11
G, 11B are digital signal processing circuits 10R, 10G,
Since the knee correction is provided after the gamma correction and the pedestal correction, it is provided in the latter stage of 10B, so that the peak level can be surely corrected to be equal to the white clip level.

As described above, the knee correction circuit 11R-
By obtaining and setting the compression ratio and knee point of 11B, the knee point will not be set below the minimum point, and the compression ratio can be set to the minimum necessary. Grows larger.

Since the low-pass filter 22 is inserted before the peak detection circuit 23, the peak detection circuit 2
The peak level detected in 3 decreases according to the area. As a result, if the area is not large to some extent, the peak level is detected to be small, so the amount of change in the knee point of the knee correction circuit is small, and the probability of compressing the necessary subject portion outside the high brightness level portion is small. .

On the contrary, even when the area is small, the knee point of the knee correction circuit can be set so that the peak level is not clipped when the important high-luminance subject is photographed, regardless of the area. It may be desired. However, with the low-pass filter 22, if the area is small, the requirement cannot be met.

To solve this, as shown in FIG.
A function of turning on / off the low-pass filter 22 is added. That is, only when the area of the high brightness level portion is small due to the switch circuit 25 and the portion is unnecessary, the switch 25 is switched to the low pass filter 22 side and turned on.

Further, as shown in FIG. 5, an amplifier 26 is provided at the output of the peak detection circuit 23, the peak detection output level is multiplied by a coefficient GC, and the peak level reduced due to the small area by the low-pass filter 22 is corrected. You may do it. It is also possible to perform the gain control processing by multiplying the coefficient GC in the system control circuit 24 without providing the amplifier 26.

By performing this calculation, the degree of change in area and knee point can be changed, and at the same time, the auto knee correction amount can be set.

[0049]

As described above, according to the present invention, the compression ratio and knee point for knee correction can always be automatically and appropriately determined.

Further, by providing the low-pass filter in front of the peak detection circuit, it is possible to prevent the necessary subject portion from being compressed due to the presence of an unnecessary high brightness portion having a small area.

When the output gain of the peak detection circuit is controlled substantially, the peak level of a small area can be accurately detected even if a low-pass filter is inserted before the peak detection circuit. Then, the degree of change of the knee point can be changed so that the small area portion can be appropriately compressed. In other words, it becomes possible to set the relationship between the area of the high brightness portion and the knee correction amount.

[Brief description of drawings]

FIG. 1 is a block diagram of a part of an embodiment of a color image pickup apparatus according to the present invention.

FIG. 2 is a continued block diagram of an embodiment of the color image pickup apparatus according to the present invention.

FIG. 3 is a diagram for explaining a main part of an embodiment of a color image pickup apparatus according to the present invention.

FIG. 4 is a block diagram of a main part of another embodiment of the color image pickup apparatus according to the present invention.

FIG. 5 is a block diagram of a main part of another embodiment of the color image pickup apparatus according to the present invention.

FIG. 6 is a diagram for explaining a knee correction circuit.

FIG. 7 is a diagram for explaining a knee correction circuit.

FIG. 8 is a diagram for explaining the relationship between the compression ratio of the knee correction circuit and the knee point.

FIG. 9 is a diagram for explaining the relationship between the compression ratio of the knee correction circuit and the knee point.

FIG. 10 is a diagram for explaining the relationship between the compression ratio of the knee correction circuit and the knee point.

[Explanation of symbols]

 1 Image sensor 9R A / D converter for red primary color signal 9G A / D converter for green primary color signal 9B A / D converter for blue primary color signal 10R Digital signal processing circuit for red primary color signal 10G Green Digital signal processing circuit for primary color signal 10B Digital signal processing circuit for blue primary color signal 11R Knee correction circuit for red primary color signal 11G Knee correction circuit for green primary color signal 11B Knee correction circuit for blue primary color signal 12R White clip circuit for red primary color signal 12G White clip circuit for green primary color signal 12B White clip circuit for blue primary color signal 21 NAM circuit 22 Low pass filter 23 Peak detection circuit 24 System control circuit 25 Switch circuit 26 For gain control Amplifier

Claims (4)

[Claims] 1. An image pickup device, means for detecting a maximum level signal of the three primary color signals from the image pickup device, and a peak detection circuit for detecting a peak level of the maximum level signal of the three primary color signals. And compressing the video signal of a high-brightness portion having a predetermined break point level or higher at a predetermined compression ratio to compress the video signal within a specified signal level, and the break point level can be variably set, A knee correction circuit in which the compression ratio can be variably set, a means for setting the break point level of the knee correction circuit according to the peak level detected by the peak detection circuit, and an input signal of the knee correction circuit. A color image pickup apparatus comprising: a signal level standard, a white clip level, and means for setting a compression ratio of the knee correction circuit based on a minimum break point level of the knee correction circuit. 2. An image pickup device, a means for detecting a maximum level signal of the three primary color signals from the image pickup device, and a peak detection circuit for detecting a peak level of the maximum level signal of the three primary color signals. And a video signal in a high-brightness area above a predetermined break point level is compressed with a predetermined compression ratio to compress the video signal within a specified signal level. The above-mentioned break point level can be variably set. A circuit and means for setting the break point level of the knee correction circuit in accordance with the peak level detected by the peak detection circuit, and means for detecting the maximum level signal of the three primary color signals; A color image pickup device comprising a low-pass filter provided between a peak detection circuit and the peak detection circuit. 3. The color image pickup apparatus according to claim 2, further comprising means for turning on / off the low-pass filter. 4. The color image pickup apparatus according to claim 2, wherein the gain of the output signal of the means for detecting the maximum level signal of the three primary color signals is adjustable.