JP5147521B2 - Image processing device - Google Patents

Description

  The present invention relates to an image processing apparatus that nonlinearly converts luminance information of a luminance signal.

  In the conventional image processing apparatus, the luminance information of the input luminance signal is shifted by the automatic black level control circuit, and then the three primary color signals are generated from the color difference signal and the converted luminance signal. Thereafter, the brightness of the three primary color signals is shifted by the brightness adjustment circuit, and then the gradations of the three primary color signals are nonlinearly converted for each input gradation by the gamma correction circuit. By the brightness adjustment and gamma correction of the three primary color signals, the luminance information of the luminance signal in the three primary color signals is converted nonlinearly. As described above, the conventional image processing apparatus nonlinearly converts the luminance information of the luminance signal before and after the generation of the three primary color signals. Patent Document 1 describes a nonlinear conversion circuit that performs such nonlinear conversion.

Japanese Patent Laid-Open No. 4-077179

  However, there is a problem that the ratio between the luminance signal and the color difference signal in the three primary color signals after the nonlinear conversion is different from the ratio between the luminance signal and the color difference signal before the nonlinear conversion due to the nonlinear conversion of the luminance information of the luminance signal. It was. As a result, color saturation is higher in the pixel portion that has been converted to have a lower luminance than that at the time of initial input by nonlinear conversion, and in the pixel portion that has been converted to have a higher luminance than at the time of initial input, There was a problem of low saturation.

  The present invention has been made to solve the above-described problems, and an image processing apparatus capable of correcting the balance between the luminance signal and the color difference signal after nonlinear conversion to the balance before nonlinear conversion is provided. The purpose is to provide.

An image processing apparatus according to the present invention includes an automatic black level control circuit that nonlinearly converts the brightness of a first luminance signal, and three primary color signals generated from the converted first luminance signal and color difference signal . A nonlinear conversion circuit including a brightness adjustment circuit and a gamma correction circuit for nonlinearly converting brightness and gradation, respectively , is provided. Then, the luminance of the first luminance signal before nonlinear conversion by the automatic black level control circuit and the three primary color signals after nonlinear conversion by the brightness adjustment circuit and the gamma correction circuit are generated. And a color difference signal correction circuit for correcting the color difference signal based on the luminance of the second luminance signal.

  According to the image processing apparatus of the present invention, the second luminance generated from the first luminance signal before nonlinear conversion by the nonlinear conversion circuit and the three primary color signals after nonlinear conversion by the nonlinear conversion circuit. The color difference signal is corrected based on the signal. Thereby, it is possible to perform correction for returning the balance between the luminance signal and the color difference signal after the nonlinear conversion to the balance between the luminance signal and the color difference signal before the nonlinear conversion.

<Embodiment 1>
The image processing apparatus according to the present embodiment is provided in, for example, a still image camera, a video camera, a television receiver, a monitor receiver, and a video storage device that perform image processing. Before describing the configuration of the image processing apparatus according to the present embodiment, the configuration of a conventional image processing apparatus will be described. FIG. 4 is a block diagram showing a configuration of a conventional image processing apparatus. As shown in the figure, the conventional image processing apparatus includes an automatic black level control circuit 1, a dematrix circuit 2, a contrast adjustment circuit 3, a brightness adjustment circuit 4, a gamma correction circuit 5, and an amplitude converter 6. A hue adjustment circuit (tint adjustment circuit) 7 and a color saturation adjustment circuit 8. The automatic black level control circuit 1 receives the luminance signal y from the outside, and the amplitude converter 6 receives the color difference signals Cb and Cr from the outside.

  The automatic black level control circuit 1 corrects the brightness of the luminance signal y from the outside. The automatic black level control circuit 1 performs correction to change the black level of the luminance signal y, that is, the brightness with time so as to always maintain the black tightness visually according to the pattern. Output a luminance signal.

The amplitude converter 6 corrects the amplitudes of the color difference signals Cb and Cr from the outside, converts them into color difference signals by and ry which are difference signals between the luminance signal and the three primary color signals, and the color difference after the conversion. The signals by and ry are output. The hue adjustment circuit 7 corrects the hue by rotating the vector angle of the color difference signals by and ry from the amplitude converter 6 according to the user's preference, and the corrected color difference signal (b− y) _t , (ry) _t is output. Color saturation adjusting circuit 8, in accordance with the preference of the user, the color difference signal from the color adjusting circuit 7 (b-y) _t, and adjust the color saturation of (r-y) _t, the color difference after the adjustment Signals (by) _ct and ( _ry ) _ct are output.

The dematrix circuit 2 uses the luminance signal from the automatic black level control circuit 1 and the color difference signals (by) _ct and ( _ry ) _ct from the color saturation adjustment circuit 8 to _provide the three primary color signals r and g. , B. The contrast adjustment circuit 3 amplifies the amplitudes of the three primary color signals r, g, and b from the dematrix circuit 2 according to the user's preference, and outputs the amplified three primary color signals. The brightness adjustment circuit 4 adjusts the black level of the three primary color signals from the contrast adjustment circuit 3, that is, the brightness according to the user's preference, and outputs the adjusted three primary color signals. The gamma correction circuit 5 nonlinearly converts the gradations of the three primary color signals from the brightness adjustment circuit 4 for each input gradation, and outputs the three primary color signals r ′, g ′, and b ′ after luminance correction.

  The values after the black level shift by the automatic black level control circuit 1 and the brightness adjustment circuit 4 described above have a lower limit determined in a practical process, and all the values after the shift below the lower limit value are processed as the lower limit value. Is done. Therefore, the automatic black level control circuit 1 can be regarded as a circuit that nonlinearly converts the luminance information of the luminance signal y before the dematrix circuit 2 that generates the three primary color signals r, g, and b. Similarly, the brightness adjustment circuit 4 can be regarded as a circuit that nonlinearly converts luminance information of luminance signals in the three primary color signals after the dematrix circuit 2 that generates the three primary color signals r, g, and b.

  Among these, the automatic black level control circuit 1 performs non-linear conversion of brightness signal brightness based on temporal changes. However, the nonlinear conversion is not linked to the processing of the color difference signal from the amplitude converter 6 to the color saturation adjustment circuit 8. Therefore, the ratio between the luminance signal corrected by the automatic black level control circuit 1 and the color difference signal converted by the color saturation adjustment circuit 8 is the ratio between the luminance signal y at the time of input and the color difference signals by and ry. (Hereinafter, sometimes referred to as a ratio at the time of input). Further, the brightness adjustment circuit 4 performs a process of shifting the luminance information of the luminance signals in the three primary color signals in the bright direction or the dark direction by the same amount from the dark gradation to the light gradation. Therefore, the ratio between the luminance signal and the color difference signal in the three primary color signals adjusted by the brightness adjustment circuit 4 also changes from the ratio at the time of input.

  Further, after the dematrix circuit 2 that generates the three primary color signals r, g, and b, the gamma correction circuit 5 converts the gradation of the three primary color signals from the brightness adjustment circuit 4 nonlinearly for each input gradation. Therefore, the gamma correction circuit 5 can be regarded as a circuit that nonlinearly converts the luminance information of the luminance signals in the three primary color signals after the dematrix circuit 2 that generates the three primary color signals r, g, and b. Similarly, the ratio of the luminance signal and the color difference signal in the three primary color signals whose luminance is corrected by the gamma correction circuit 5 is also changed from the ratio at the time of input.

  As described above, the nonlinear conversion circuit including the automatic black level control circuit 1, the brightness adjustment circuit 4, and the gamma correction circuit 5 converts the luminance information of the luminance signal into a non-linear manner before and after the dematrix circuit 2 that generates the three primary color signals. Was. As a result of this non-linear conversion, there is a problem that the ratio between the luminance signal and the color difference signal in the three primary color signals finally output from the image processing apparatus is different from the ratio at the time of input.

  FIG. 1 is a block diagram of a configuration of an image processing apparatus according to the present embodiment for solving such a problem. Hereinafter, among the configurations of the image processing apparatus according to the present embodiment, configurations that are not newly described are assumed to be substantially the same as those described above, and are denoted by the same reference numerals. As shown in the figure, the image processing apparatus according to the present embodiment includes a luminance signal generation circuit 9, a color difference signal correction circuit 10, and a dematrix circuit 11 in addition to the above-described configuration.

  The automatic black level control circuit 1 converts the brightness of the first luminance signal y nonlinearly and converts the luminance information of the luminance signal nonlinearly before the dematrix circuit 2. The dematrix circuit 2 is based on the first luminance signal nonlinearly converted by the automatic black level control circuit 1 and the chrominance signals by and ry converted by the amplitude converter 6 and outputs the three primary color signals r. , G, b are generated. After the dematrix circuit 2, the brightness adjustment circuit 4 nonlinearly converts the brightness of the three primary color signals r, g, and b, and nonlinearly converts the luminance information of the luminance signal in the three primary color signals. After the dematrix circuit 2, the gamma correction circuit 5 converts the gradations of the three primary color signals r, g, and b nonlinearly for each input gradation, and converts the luminance information of the luminance signal in the three primary color signals nonlinearly. . Then, the gamma correction circuit 5 outputs three primary color signals r ′, g ′, and b ′ obtained by nonlinearly converting the luminance information of the luminance signal.

  Thus, the non-linear conversion circuit composed of the automatic black level control circuit 1, the brightness adjustment circuit 4, and the gamma correction circuit 5 uses the three primary color signals generated from the first luminance signal y and the color difference signals by and ry. The luminance information of the luminance signal is converted non-linearly before and after the dematrix circuit 2.

  Here, the first luminance signal y input to the automatic black level control circuit 1, the color difference signals by and ry input to the dematrix circuit 2, and the three primary colors output from the gamma correction circuit 5. The relationship with the signals r ′, g ′, and b ′ is expressed as in Equation (1). The function f of the equation (1) is a conversion process from the automatic black level control circuit 1 to the gamma correction circuit 5, that is, the nonlinearity in the automatic black level control circuit 1, the brightness adjustment circuit 4, and the gamma correction circuit 5. Represents a conversion process that includes conversion.

  The luminance signal generation circuit 9 generates a second luminance signal y ′ based on the three primary color signals r ′, g ′, b ′ after nonlinear conversion output from the gamma correction circuit 5. The luminance signal generation circuit 9 according to the present embodiment linearly generates a second luminance signal y ′ from the three primary color signals r ′, g ′, and b ′ after nonlinear conversion based on the equation (2). . Here, k, l, and m are predetermined coefficients.

The color difference signal correction circuit 10 generates a color difference signal (g−y) _ct based on the color difference signals (b−y) _ct and (r−y) _ct . The luminance signal generation circuit 9 according to the present embodiment generates a color difference signal (g−y) _ct from the color difference signals (by) _ct and ( _ry ) _ct based on Expression (3). Here, s and t are predetermined coefficients.

The color difference signal correction circuit 10 included in the image processing apparatus according to the present embodiment has a non-linear conversion by the non-linear conversion circuit and the non-linear conversion by the non-linear conversion circuit and the non-linear conversion by the non-linear conversion circuit. of the three primary color signals r ', g', on the basis of b on the luminance of the 'from the second luminance signal y generated linearly', the color difference signal _{(b-y) ct, (} r-y) ct, (g -Y) Correct _ct . In the present embodiment, the color difference signal correction circuit 10 has the luminance of the first luminance signal y before nonlinear conversion by the above-described nonlinear conversion circuit and the three primary color signals r after nonlinear conversion by the nonlinear conversion circuit. A luminance ratio (= y ′ / y) with the luminance of the second luminance signal y ′ generated from “, g”, b ′ is calculated in units of pixels. That is, the luminance change rate is calculated. Then, the color difference signal (b-y) _ct of the corresponding pixel, (r-y) _ct, the amplitude of the (g-y) _ct, as shown in Equation (4), the luminance ratio described above (= y '/ y) is multiplied and corrected, and the corrected color difference signals (by) ′, (gy) ′, and (ry) ′ are output.

The dematrix circuit 11 includes the color difference signals (by) ′, (gy) ′, (ry) ′ corrected by the color difference signal correction circuit 10, and the non-linear conversion output from the luminance signal generation circuit 9. Based on the subsequent second luminance signal y ′, corrected three primary color signals r _out , g _out and b _out are generated. The dematrix circuit 11 according to the present embodiment is obtained from the color difference signals (b−y) ′, (g−y) ′, (r−y) ′ and the second luminance signal y ′ according to the equation (5). Based on this, three primary color signals r _out , g _out and b _out are generated and output.

According to the image processing apparatus according to the present embodiment as described above, the ratio of the luminance signal and the color difference signal in the three primary color signals output from the above-described nonlinear conversion circuit is input to the above-described nonlinear conversion circuit. Correction processing for returning to the ratio between the first luminance signal y and the color difference signals by and ry before being performed can be performed for each pixel. Thus, in an apparatus to which the three primary color signals r _out , g _out , and b _out are input, an image in which the ratio between the luminance signal and the color difference signal is corrected for each pixel, that is, the natural color saturation of the pixel is corrected. Video can be displayed.

<Embodiment 2>
FIG. 2 is a block diagram showing the configuration of the image processing apparatus according to this embodiment. Of the configurations of the image processing apparatuses according to the following embodiments, the same configurations as those of the image processing apparatus according to the first embodiment are denoted by the same reference numerals, and the configurations not newly described are described in the first embodiment. Shall be the same. In the configuration of the image processing apparatus according to the first embodiment shown in FIG. 1, the hue adjustment circuit 7 and the color saturation adjustment circuit 8 are arranged in front of the color difference signal correction circuit 10. On the other hand, in the configuration of the image processing apparatus according to the present embodiment illustrated in FIG. 2, the hue adjustment circuit 7 and the color saturation adjustment circuit 8 are disposed after the color difference signal correction circuit 10. The image processing apparatus according to the present embodiment is different from the first embodiment in that the arrangement of the hue adjustment circuit 7 and the arrangement of the color saturation adjustment circuit 8 are different, but the image processing apparatus according to the present embodiment is also different. The same effects as those of the first embodiment can be obtained.

<Embodiment 3>
FIG. 3 is a block diagram showing a configuration of the image processing apparatus according to the present embodiment. In the image processing apparatus according to the first embodiment shown in FIG. 1, the color difference signal _{(b-y) ct, (} r-y) ct, the (g-y) _ct, the first luminance signal y and the second luminance The luminance ratio (= y ′ / y) of the signal y ′ is multiplied as it is. On the other hand, in the image processing apparatus according to this embodiment, the luminance ratio (= y ′ / y) used in the color difference signal correction circuit 10 can be amplified or attenuated. This will be described below.

  As shown in FIG. 3, the image processing apparatus according to the present embodiment further includes an increase / decrease unit 12 and an adder 13 in addition to the configuration of the first embodiment. The increase / decrease unit 12 is provided after the luminance signal generation circuit 9. The increase / decrease unit 12 includes, for example, an amplifier and an attenuator. The increase / decrease unit 12 outputs a second luminance signal my 'obtained by multiplying the luminance of the second luminance signal y' by a coefficient m. The adder 13 adds the luminance of the second luminance signal my ′ from the increase / decrease unit 12 to the luminance of the second luminance signal y ′ from the luminance signal generation circuit 9 to generate a second luminance signal (1 + m) y ′. Is output.

Similar to the first embodiment, the color difference signal correction circuit 10 generates a color difference signal (g−y) _ct from the color difference signals (by) _ct and (r−y) _ct based on Expression (3). . Then, the color difference signal correction circuit 10 determines the color difference signal (by) _ct , based on the luminance of the first luminance signal y and the luminance of the second luminance signal (1 + m) y ′ from the adder 13. (Ry) _ct , ( _gy ) _ct is corrected. In the present embodiment, the color difference signal correction circuit 10 has a luminance ratio between the luminance of the first luminance signal y and the luminance of the second luminance signal (1 + m) y ′ from the adder 13 (= (1 + m) · y ′ / y) is calculated in units of pixels. The corresponding color difference signals of the pixels _{(b-y) ct, (} r-y) ct, the amplitude of the (g-y) _ct, as shown in equation (6), the luminance ratio (= (1 + m) · y ′ / y) is used for correction, and corrected color difference signals (by) ′, (g−y) ′, and (r−y) ′ are output. Subsequent operations are the same as those in the first embodiment.

  In the image processing apparatus according to the present embodiment configured as described above, the same effects as those of the first embodiment can be obtained. Further, according to the image processing apparatus according to the present embodiment, since the luminance ratio used in the color difference signal correction circuit 10 can be amplified or attenuated, the balance between the luminance signal output from the image processing apparatus and the color difference signal is finely adjusted. Can be adjusted.

1 is a block diagram illustrating a configuration of an image processing device according to Embodiment 1. FIG. 6 is a block diagram illustrating a configuration of an image processing apparatus according to Embodiment 2. FIG. FIG. 10 is a block diagram illustrating a configuration of an image processing device according to a third embodiment. It is a block diagram which shows the structure of the conventional image processing apparatus.

Explanation of symbols

  1 automatic black level control circuit, 2, 11 dematrix circuit, 3 contrast circuit, 4 brightness adjustment circuit, 5 gamma correction circuit, 6 amplitude converter, 7 hue adjustment circuit, 8 color saturation adjustment circuit, 9 luminance signal generation circuit 10 color difference signal correction circuit, 12 increase / decrease unit, 13 adder.

Claims (3)

An automatic black level control circuit that nonlinearly converts the brightness of the first luminance signal, and the brightness and gradation of the three primary color signals generated from the converted first luminance signal and color difference signal are respectively nonlinearly converted. A non-linear conversion circuit including a brightness adjustment circuit and a gamma correction circuit ,
A second luminance generated from the luminance of the first luminance signal before nonlinear conversion by the automatic black level control circuit and the three primary color signals after nonlinear conversion by the brightness adjustment circuit and the gamma correction circuit. A color difference signal correction circuit for correcting the color difference signal based on the luminance of the luminance signal;
Image processing device. The color difference signal correction circuit includes:
The second luminance generated from the luminance of the first luminance signal before nonlinear conversion by the automatic black level control circuit and the three primary color signals after nonlinear conversion by the brightness adjustment circuit and the gamma correction circuit. Calculating a luminance ratio with the luminance of the luminance signal of each pixel, and multiplying the amplitude of the color difference signal of the corresponding pixel by the luminance ratio,
The image processing apparatus according to claim 1. The luminance ratio used in the color difference signal correction circuit can be amplified or attenuated.
The image processing apparatus according to claim 2.

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