JP3971550B2 - Image signal processing circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image signal processing circuit for detecting a specific color from an image signal.
[0002]
[Prior art]
FIG. 1 shows a conventional circuit for detecting a specific color from an image signal.
[0003]
As shown in FIG. 1, an analog PreKnee processing circuit 1 compresses a high-intensity signal for each of the R, G, and B channels constituting the image signal. FIG. 2A shows input / output characteristics of the PreKnee processing circuit 1, and compresses an input signal at a level higher than the Knee point. FIG. 2B shows an input video level (RGB signal) with respect to the brightness (light quantity) of a subject when a specific color (in the example, a color close to skin color) is imaged. FIG. 2C shows the video level after the video signal has passed through the PreKnee processing circuit. FIG. 2D shows the luminance signal level obtained from the RGB signal after the PreKnee processing circuit of the same signal. Therefore, the entire dynamics of the image signal is suppressed by the PreKnee processing circuit 1 and converted into a digital signal by the A / D (analog / digital) converter 2. The image signal after A / D conversion is input to the two color detectors 3 and 4, and each color detector examines the ratio between any two color pairs (for example, R, G and R, B), When the ratio is within the range set for the specific color to be detected (for example, two colors of each pair within the set range (set range RG1, BR1) indicated by hatching in FIGS. 3A and 3B) When there is a ratio between them, a key signal is output. 3A and 3B show R and G, B and R ratios according to the luminance of a specific color. In the case of an achromatic color, since the ratio of R, G, and B is 1: 1: 1, each becomes a straight line having an inclination of 45 degrees.
[0004]
Reference numeral 5 denotes a luminance determiner, which determines the luminance of the image signal after A / D conversion by the A / D converter 2, and the hue of the image signal gathers to narrow the determination range (FIG. 3). In the low luminance part (1) of A), a luminance judgment signal (for example, low at low luminance, and low otherwise) is not output from the mixer 6 even if a key signal is output from the color detector. Hi pulse). The mixer 6 mixes the key signals from the two color detectors 3 and 4 and outputs the mixed signal as a key signal only when the luminance determination signal from the luminance determination unit 6 is Hi.
[0005]
If the mix of the key signals from the color detectors 3 and 4 is within the desired setting range with the two color detectors, and if the specific color to be detected is to be detected, the overlapping portion of the two key signals For example, an AND of two key signals is obtained so as to be detected.
[0006]
[Problems to be solved by the invention]
In the conventional method described above, when any of R, G, and B of the image signal is subjected to luminance compression (FIG. 2) by analog PreKnee processing, the ratio between R, G, and B is the ratio before compression. For example, as shown in FIG. 3A, there is a case where the color detector does not detect after compression even if it is within the set range RG1 between R and G before compression. That is, the ratio between R and G and the ratio between B and R within the set range RG1 before compression are the compression start by the PreKnee processing circuit, as indicated by solid lines in FIGS. Level (indicated by the arrow indicated as “Bending by PreKnee” in the figure) is different from the original setting range RG1 (indicated by hatching). As an example of such a false detection, for example, in the case of an image signal showing a face, when the light hits the cheek or forehead that should be the same color, the portion that is brightly reflected is compressed by the PreKnee circuit as much. Since the original skin color is close to white, the key signal is erroneously detected. Therefore, in the conventional method, the luminance corresponding to (2) in (D) in FIG. 2 ((2) in (A) in FIG. 3 and (2) in (B) in FIG. The luminance threshold 2 is provided so as to suppress the key signal at a high level.
[0007]
An object of the present invention is to provide an image signal processing circuit that solves the problem described above.
[0008]
[Means for Solving the Problems]
Therefore, the present inventor mainly caused the erroneous detection of the high-luminance portion because the ratio of R, G, and B changes due to the increase in the luminance of the image signal by the PreKnee process. In the color detector, on the basis of the compression start point of the PreKnee process, if the luminance is higher than that, a different range is set for the ratio of the two colors at the time of color detection, and the color is determined according to the luminance of the image signal. It was noted that the setting range at the time of detection should be switched. It should be noted that the portion close to low-luminance black in (1) in FIG. 3 (A) and (1) in FIG. 3 (B) is not determined as in the conventional method.
[0009]
The present invention has been made based on the above findings, the invention of claim 1 includes a first color detection means for detecting a specific color from an image signal compressed by Plinian (PreKnee) process, it is compressed by the Prinny treatment Second color detecting means for detecting the specific color when the image signal is larger than the knee point, and the detection output of the first color detecting means and the second color detecting means according to the luminance of the image signal compressed by the pre-needle processing . Output means for outputting one of the detection outputs of the two-color detection means.
[0010]
According to a second aspect of the present invention, in the first aspect, the output unit includes a luminance detection unit that detects luminance of the image signal compressed by the pliny process, and the first detection unit according to a detection result of the luminance detection unit. And switching means for selecting and outputting either the detection output of the one color detection means or the detection output of the second color detection means.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 4 shows an embodiment of the present invention. The analog PreKnee processing circuit 1, the A / D converter 2, and the two color detectors 3 and 4 have the same configuration as in FIG. 1, and the two color detectors 3 and 4 are detected as shown in FIG. When the setting ranges RG1 and BR1 are set for the specific color to be set, and the ratio between the two colors of each pair (R, G and B, R) of the input image signal is within the setting ranges RG1 and BR1 Output key signal. The key signals from the two color detectors 3 and 4 are mixed and output in the mixer 9.
[0012]
The image signal converted into a digital signal by the A / D converter 2 is further input to the two color detectors 7 and 8 with offset. As shown in FIG. 5, the color detectors 7 and 8 have set ranges RG2 and BR2 different from the set ranges RG1 and BR1. The setting ranges RG2 and BR2 are obtained as follows. That is, with respect to the setting ranges RG1 and BR1 set for the specific color to be detected, the compression rate at the time of PreKnee processing by the PreKnee processing circuit 1, that is, an input / output characteristic curve at a level higher than, for example, the Knee point in FIG. The other setting ranges RG2 and BR2 are obtained by applying an offset in accordance with the inclination of.
[0013]
Therefore, the two color detectors 7 and 8 with offset are between any two color pairs (for example, R, G and R, B) of the image signal after A / D conversion from the A / D converter 2. The ratio is checked, and a key signal is output when the ratio between the two colors of each pair is within a certain range within the setting ranges RG2 and BR2 set for the specific color to be detected. The key signals from the two color detectors 7 and 8 are mixed and output in the mixer 10.
[0014]
The luminance determiner 11 outputs one of three types of determination signals based on the image signal after A / D conversion from the A / D converter 2. That is, a low-luminance portion where hues in the image signal after A / D conversion from the A / D converter 2 gather, that is, a luminance portion that prevents the key signal from being output in a portion close to black is designated. 1 determination signal, a second determination signal that designates a higher luminance level than the luminance level corresponding to the Knee point, for example, as shown in FIG. 2, and a higher luminance level. One of the third determination signals for designating the part is output. In FIG. 5, the boundary between the first determination signal output and the second determination signal output is the luminance threshold 1, and the boundary between the second determination signal output and the third determination signal output is the luminance threshold 2. It is shown.
[0015]
The switch 12 receives the key signals from the two mixers 9 and 10 and responds to the three types of determination signals from the luminance determiner 11,
(1) No key signal is output from either of the two mixers 9 and 10 for the first determination signal.
(2) Only the key signal from the mixer 9 is output for the second determination signal.
(3) Only the key signal from the mixer 10 is output for the third determination signal.
One of the three operations is executed.
[0016]
Therefore, the image signal after A / D conversion from the A / D converter 2 does not output a key signal for a portion that detects low-brightness black in which hues gather as shown in FIG. For a portion having a higher luminance level and lower than the luminance level corresponding to the Knee point as shown in FIG. 2, for example, the two color detectors 3 and 4 described above based on the setting ranges RG1 and BR1. The color detection processing is performed as described above, and the portions having higher luminance levels are subjected to the color detection processing as described above in the two offset color detectors 7 and 8 based on the setting ranges RG2 and BR2. Among the signals, even if the portion of the signal is compressed by the analog PreKnee processing circuit 1 and the color ratio is lost and changed, accurate specific color detection suitable for it is performed.
[0017]
The two color detectors with offsets 7 and 8 perform an operation for obtaining the same effect as the offset for the input image signal, and the ratio between the two color pairs after the operation is two colors. Whether or not the key signal can be output may be determined according to whether or not the detectors 3 and 4 are within the same setting range as the setting ranges RG1 and BR1.
[0018]
In addition, the above explanation is for R, G, B, that is, three primary color signals. However, it is obvious that the present invention can be similarly applied to an image signal composed of luminance and color difference signals.
[0019]
【The invention's effect】
As described above, according to the present invention, when a specific color is detected from an image signal, for example, the color ratio is lost due to analog PreKnee processing, and accurate specific color detection can be realized even for a changed hue.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a conventional image signal processing circuit.
FIG. 2 is a diagram showing an example of PreKnee processing characteristics by the circuit.
FIGS. 3A and 3B are diagrams respectively showing setting ranges between two different color pairs for detecting a specific color in the circuit.
FIG. 4 is a diagram illustrating an image signal processing circuit according to the embodiment of the present invention.
FIGS. 5A and 5B are diagrams respectively showing two setting ranges between two different color pairs for detecting a specific color in the circuit.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 PreKnee processing circuit 2 A / D converter 3, 4 Color detector 7, 8 Color detector with offset 11 Luminance determination device 12 Switch

Claims (2)

First color detection means for detecting a specific color from an image signal compressed by a pre-Knee process ;
Second color detection means for detecting the specific color when an image signal compressed by the plenary process is larger than a knee point ;
Output means for outputting either the detection output of the first color detection means or the detection output of the second color detection means in accordance with the luminance of the image signal compressed by the pliny process. Image signal processing circuit. In claim 1,
The output means includes a brightness detection means for detecting the brightness of the image signal compressed by the pliny process, and a detection output of the first color detection means and a second color detection means according to a detection result of the brightness detection means. Switching means for selecting and outputting any one of the detected outputs of the image signal processing circuit.

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