JP3348311B2 - Video signal processing apparatus and method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a video signal processing apparatus and method for improving color reproduction in a color television camera or the like, for example, reproduction of skin color.

[0002]

2. Description of the Related Art The quality of color reproduction in a color television camera largely depends on the light source under which the image is taken. For example, the image is taken outdoors under sunlight and indoors under fluorescent light. The color reproducibility is significantly different from that of imaging. In particular, a single-panel color television camera using a complementary color imager (hereinafter referred to as a complementary color television camera)
Although high sensitivity can be obtained, many improvements are desired in terms of fidelity of color reproduction, and various adjustment means are provided for this purpose. One example of such adjusting means will be described with reference to FIG.

FIG. 1 shows a signal processing system for deriving a color difference signal from an image pickup output of a CCD image sensor in a conventional complementary color television camera, and an automatic adjustment circuit provided in the signal processing system. It is. In this figure, the imaging output from the CCD image sensor 2 is
Is supplied to the CDS circuit 4 through which the correlation double sampling is performed to reduce noise. Next, the AGC circuit 5
, And to the sample and hold circuits 6 and 7, to which pulses P1 and P2 receive signals from every other pixel in a relationship as shown in the pixel arrangement of the complementary imager of FIG. Supplied to sample.

On the other hand, the image pickup output from the CCD image sensor is an output obtained by mixing signals for two pixels in the vertical direction as shown in FIG.
8 and 9 for quantizing and encoding the outputs of
Is supplied to the addition / subtraction circuit through the adder, thereby obtaining Mg + Ye + G + Cy = 3G + 2R + 2B = Y1 from the addition circuit.

From the subtraction circuit, on the N line, Mg + Ye- (G + Cy) = 2RG = C0 is obtained, and on the N + 1 line, Ye + G- (Mg + Cy) = G-2B = -C1 is obtained.

The Y1 signal is supplied to a primary color separation matrix 14 via a low-pass filter 10, and the output of the subtraction circuit is supplied to a synchronization circuit 12 including a one-line delay element 1HDL. The signal C0 is taken out at the output side of the. The signal on the other output side of the synchronization circuit is passed through the polarity inversion circuit 13 to extract the signal C 1, and the signals C 0 and C 1 are also supplied to the primary color separation matrix 14. In the primary color separation matrix 14, primary color signals R, G, and B are formed from the signals Y1, C0, and C1 by the matrix. The primary color signals R, G, and B are subjected to white balance adjustment in a circuit 15 and gamma adjustment in a circuit 16, and then matrixed in a circuit 17 to form color difference signals RY and B.
-Y is formed.

The microcomputer 20 is a control device for executing automatic adjustment. The microcomputer 20 receives a signal from a light receiving amount sensor provided in a complementary color television camera, and controls the aperture 1 and the AGC circuit 5 based on the signal. An image signal of an appropriate level is always obtained regardless of the amount of received light. Also, the Y1, C0, and C1 signals are fetched through the interface 19, and the white balance adjustment in the circuit 15 is executed based on these signals. The white balance is adjusted as follows. First, in the initial adjustment of the complementary color television camera, the white balance is adjusted so that a correct white balance can be obtained in an imaging state under illumination light having a predetermined color temperature.

Here, the color temperature of sunlight changes greatly from a low value to a high value depending on weather conditions and the like, and its change characteristics are, for example, R / G on the vertical axis and B / G on the horizontal axis. B /
On the G─R / G plane, the trajectory is along the blackbody radiation locus Z as schematically shown in FIG. 5, so that the change in the white balance caused by the color temperature change is corrected as follows. Perform automatic adjustment. That is, in normal imaging, R, G, B
Since the average of the signal over the entire screen becomes almost white, the microcomputer 20 outputs Y1 through the interface 19.
A signal, a C0 signal, and a C1 signal are taken in, an average value of the R, G, and B signals over the entire screen (these values are written as <R>, <G>, and <B>) is obtained based on these signals.
The values of <R> / <G> and <B> / <G> are calculated.

[0009] These <R> / <G> and <B>
The deviation between the value of> / <G> and “1” is regarded as the deviation of the white balance, and the gains of R, G, and B in the white balance adjustment circuit 15 in FIG. 3 are adjusted so that this becomes equal to “1”. adjust. Specifically, for example, the gain of the R signal is set to <G> / <
R> times and the gain of the B signal is <G> / <B>
Double it. In some cases, the image is in an imaging state in which the entire screen is substantially a single color (for example, when a lawn or a blue sky is imaged on the entire screen), so that the average value of the R, G, B signals over the entire screen is When the chromaticity value is in the vicinity of white (for example, a square ACDE surrounding the white point W in FIG. 5)
White balance adjustment according to the deviation of the white balance.

[0010]

The automatic white balance adjustment function as described above can improve color reproducibility in outdoor imaging, but in indoor imaging under fluorescent light, the spectrum of the light source can be improved. Are separated from those on the blackbody radiation trajectory, so that only the automatic white balance adjustment described above does not provide a sufficient improvement in color reproducibility. FIG. 6 shows the position on the vectorscope of each color bar when a color bar pattern is captured by a complementary color television camera having the above-described automatic white balance adjustment function under various light sources.

In this figure, ● represents an ideal position of each color bar when an image is taken under sunlight. In addition, ○ indicates the position of each color bar when imaged under various fluorescent lamps, and each ○ indicates the position of the color bar when imaged under one specific type of fluorescent lamp. As shown in this figure, the white color bar W is always located at the origin while the white balance is always maintained by the above-mentioned automatic white balance adjustment operation, but the chromatic color bars Ye, Cy, G, R, and M are displayed.
For both g and B, the chromaticity point considerably changes depending on the type of fluorescent lamp, causing color shift. For example, when looking at the positions of red R and yellow Ye that greatly affect the reproduction of skin color, The yellow chromaticity point significantly changes in the negative direction of the BY axis, and this causes a phenomenon in which the skin color becomes yellowish in imaging under a fluorescent lamp.

The present invention has been made in order to solve such a problem, and a color signal correction apparatus capable of reproducing a good chromatic color even when photographing under any kind of fluorescent lamp. And a method.

[0013]

According to the present invention, there is provided a video signal processing apparatus comprising: a primary color signal generating means for generating three primary color signals based on an image signal picked up by an image sensor; A shift calculating means for calculating an amount indicating the shift in balance, a white balance adjusting means for adjusting the white balance of the three primary color signals based on the amount indicating the shift in white balance, and an output from the white balance adjusting means. A color difference signal generating means for generating a color difference signal based on the three primary color signals of which the white balance has been adjusted, and detecting a shift from a black body radiation trajectory of the light source based on the three primary color signals to perform shooting under a fluorescent light source. Light source determining means for determining whether or not there is, and color difference signal correcting means for correcting the color difference signal, wherein the color difference signal correcting means, under the fluorescent light source by the determining means If it is determined that the shadow, and corrects the color difference signals.

[0014]

In the video signal processing method according to the present invention, three primary color signals are generated based on an image pickup signal picked up by an image sensor, and an amount representing white balance deviation is calculated based on the three primary color signals. The white balance of the three primary color signals is adjusted based on the amount representing the deviation of the white balance, a color difference signal is generated based on the three primary color signals having the adjusted white balance, and the black body radiation of the light source is determined based on the three primary color signals. By detecting a deviation from the trajectory, determining whether or not the image is captured under a fluorescent light source, and correcting the color difference signal when determining that the image is captured under a fluorescent light source. .

[0016]

According to the present invention, not only the deviation of the white balance caused according to the type of each fluorescent lamp in the imaging under the fluorescent light source but also the chromatic color remaining in the color difference signal after the white balance adjustment is corrected. The reproduction error is also automatically improved.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention uses a color signal correction circuit shown in FIG. 7 as a circuit for correcting the chromatic color shift described in FIG. This circuit receives the RY signal and the BY signal output from the color difference signal matrix circuit 17 of the signal processing circuit shown in FIG. , 31 and the color difference signals RY ′ and BY ′ corrected by further adjusting the level are output.

The variable amplifier 32 in this circuit
Is the hue adjustment amount for the BY signal, the gain r of the variable amplifier 33 is the hue adjustment amount for the RY signal, the gain α of the variable amplifier 34 is the amplitude adjustment amount for the RY signal, and the variable amplifier The gain β of 35 represents the amplitude adjustment amount for the BY signal, and the hue and amplitude of both color difference signals can be independently and freely changed by appropriately operating these adjustment amounts. When the relationship between the input and output signals in the correction circuit is expressed by a mathematical expression, the following [Equation 1] is obtained.

[0019]

(Equation 1)

As described above, the color signal correction circuit according to the present invention has a high correction capability for an arbitrary chromatic color. Here, by using the color signal correction circuit, the above-described fluorescent light source is used. An embodiment in which the phenomenon in which the skin color takes on a yellow tint in the lower imaging will be described. The degree of the color shift of the chromatic color under the fluorescent light source described above is correlated with the degree of the white balance shift due to the use of the fluorescent light source, and in order to suppress the phenomenon in which the skin color takes on a yellow tint. It is considered effective to suppress the level of the BY signal.

Therefore, in the present embodiment, the microcomputer 20 shown in FIG.
By setting the gain β of the Y signal as in the following equation (1), setting the values of r and s to “0” and setting the value of α to “1”, the skin color reproduction is improved. β = 0.33 + 0.35 <B> / <G> (1) (where, <B> / <G> are values obtained by the microcomputer 20 at the time of the white balance adjustment). The flowchart of the microcomputer 20 for executing the white balance adjustment and the improvement of the skin color reproduction described above can be configured as shown in FIG. 1, for example.

This flowchart will be described.
In ST1, the average value of each color signal is obtained, and it is checked whether or not the color point on the R / G ／ B / G plane determined by these average values is in the white point vicinity area where white balance should be adjusted (ST2). When it is within the area, white balance adjustment is performed (ST3). Next, it is checked whether or not the color point on the R / G ／ B / G plane is located substantially on the blackbody radiation locus (ST4). In the case of imaging, the gain of the BY signal in the above-described color signal correction circuit is set as in equation (1) to improve the reproduction of skin color (ST5).

Next, the effect of skin color improvement by the color signal correction circuit configured as described above will be specifically described for the case of imaging under a three-wavelength fluorescent lamp and the case of imaging under a white fluorescent lamp. explain. 1) In the case of a three-wavelength fluorescent lamp In this case, in the microcomputer 20, <R> / <G> = 0.71, <B> /
Based on the fact that <G> = 1.49 is obtained, the gain β of the BY signal in the color signal correction circuit is set as β = 0.33 + 0.35 <B> / <G> = 0.85. . As a result, the output B-
Y ′ and RY ′ are as follows: RY ′ = RY BY ′ ′ = 0.85 (BY).

2) In the case of a white fluorescent lamp In this case,
In the microcomputer 20, <R> / <G> = 0.90 and <B> / <G> = 0.81 as values representing the deviation of the white balance.
Is obtained, the gain β is set as follows. β = 0.33 + 0.35 <B> / <G> = 0.61 Thereby, the outputs BY ′ and R− of the color signal correction circuit are obtained.
Y ′ is RY ′ = RYBY ′ ′ = 0.61 (BY).

FIG. 2 shows the reproduction chromaticity of the Ye color bar when the color bar pattern is imaged in the above two cases. In this drawing, W1 is a chromaticity point of Ye when color signal correction is not performed in imaging under a white fluorescent lamp, and W2 is Ye reproduction when color signal correction is performed on W1 according to the present embodiment. A chromaticity point, T1 is a reproduction chromaticity point of Ye when color signal correction is not performed in imaging under a three-wavelength fluorescent lamp, and T2 is a reproduction chromaticity point of Ye when color signal correction is performed on T1. Respectively.

As is apparent from this figure, in the present embodiment, the chromaticity of reproduction of Ye is greatly improved in the imaging under any fluorescent light, and the phenomenon that the skin color becomes yellowish under the fluorescent light source is sufficiently suppressed. can do. In the present embodiment, the color signal correction circuit is applied for improving skin color reproduction.
The color signal correction circuit itself can freely correct any chromatic color by operating each adjustment amount, and the correction target is, of course, not limited to flesh color, but is extremely versatile. It is.

[0027]

According to the present invention, it is possible to automatically improve a chromatic color reproduction error that occurs depending on the type of fluorescent lamp in imaging under a fluorescent lamp light source. For example, it is possible to prevent a skin color from becoming yellowish. it can.

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating operations of white balance adjustment and color signal correction according to an embodiment of the present invention.

FIG. 2 is a diagram showing an operation and effect of color signal correction in the embodiment.

FIG. 3 is a diagram illustrating a signal processing system and an automatic adjustment circuit for deriving a color difference signal in a conventional single-panel color television camera using a complementary color imager.

FIG. 4 is a diagram illustrating a pixel array of a complementary color imager.

FIG. 5 is a diagram illustrating an area on a B / GR-G / G plane where white balance adjustment is performed.

FIG. 6 is a diagram showing positions on a vector scope after white balance adjustment when a color bar pattern is imaged under various light sources.

FIG. 7 is a diagram showing a configuration of a color signal correction circuit according to the present invention.

[Explanation of symbols]

2: CCD image sensor, 14: primary color separation matrix circuit, 15: white balance adjustment circuit, 17: color difference signal matrix circuit, 19: interface, 20: microcomputer, 30, 31, addition circuit, 32-35: variable gain amplifier,

Continuation of the front page (56) References JP-A-3-192987 (JP, A) JP-A-2-46090 (JP, A) JP-A-2-50693 (JP, A) JP-A-4-160892 (JP) , A) JP-A-2-194792 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04N 9/00-9/78

Claims (5)

(57) [Claims] 1. A primary color signal generating means for generating three primary color signals based on an image pickup signal taken out by an image sensor, a shift calculating means for calculating an amount representing a shift in white balance based on the three primary color signals, White balance adjustment means for adjusting the white balance of the three primary color signals based on the amount representing the deviation of the white balance; and a color difference signal based on the white balance adjusted three primary color signals output from the white balance adjustment means. A color difference signal generating means for generating a color difference signal; a light source determining means for detecting a shift from a black body radiation locus of a light source based on the three primary color signals to determine whether or not shooting is performed under a fluorescent light source; A color difference signal correction unit that corrects a signal, wherein the color difference signal correction unit outputs the color difference signal when the determination unit determines that the image is captured under a fluorescent light source. A video signal processing device for correcting. 2. The deviation calculating means calculates an average value of the entire screen for each color of the three primary color signals, and calculates an average value of the entire screen of another color signal with respect to the average value of the entire screen for a specific color signal. 2. The ratio of the white balance is calculated, and the ratio is output as an amount representing the deviation of the white balance.
Video signal processing device. 3. The video signal processing apparatus according to claim 1, wherein the color difference signal correction means controls the amplitude of the BY signal based on an amount representing a shift in white balance. . 4. The color difference signal correcting means according to claim 1, wherein the ratio of the average value of the entire screen of the blue signal to the average value of the entire screen with respect to the green signal is (<B> / <G>). 4. The video signal processing device according to claim 3, wherein the correction is performed by multiplying by (0.33 + 0.35 × (<B> / <G>)). 5. A three-primary-color signal is generated based on an image pickup signal taken out by an image pickup device, and an amount representing a shift in white balance is calculated based on the three-primary-color signal. The white balance of the three primary color signals is adjusted based on the three primary color signals, a color difference signal is generated based on the three primary color signals having the adjusted white balance, and a deviation from the black body radiation locus of the light source is detected based on the three primary color signals. , It is determined whether or not shooting is performed under a fluorescent light source, and when it is determined that shooting is performed under a fluorescent light source,
A video signal processing method comprising correcting the color difference signal.