JP2009111894A - Video signal processing device, imaging apparatus and video signal processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform optimal control so as not to leave unnaturalness in a look by enhancing coloring of a portion on which dynamic range compression processing has been performed by a luminance signal, with a little circuit increase, preventing early fading, and dynamically changing, in accordance with a picture pattern, color leaving processing in a high luminance area during luminance knee correction. <P>SOLUTION: A video signal processing device includes: a luminance generating section 11 for extracting a luminance signal from an input video signal; a subtraction section 15 for subtracting the luminance signal from a color component signal; an arithmetic section 18 which calculates correction coefficients Kw, Kw' based on a signal NAMY calculated based on a maximum value of color component signals of the video signal after LPFing the video signal and a coefficient CHMAX relating to a saturation level of the color component signals and implements knee correction on a luminance signal Y using at least the correction coefficients Kw, Kw'; and an addition section 19 which adds the luminance signal on which the knee correction has been implemented, and an output of the subtraction section 15 and outputs the video signal to which the knee correction has been applied. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to, for example, a video signal processing apparatus, and more particularly to a technical field that optimally adjusts color surroundings and accompanying unnaturalness of coloring.

  Conventionally, in the field of video signal processing, knee correction is performed in which the dynamic range of a video signal is compressed and nonlinear conversion is performed in accordance with knee characteristics during the compression.

  In other words, this knee correction is a nonlinear compression process that compresses a video signal of a high-luminance portion above a predetermined level at a high compression rate, and performs knee correction for each of R, G, and B (hereinafter referred to as “knee correction”). , “RGB knee correction”) and broadly divided into those that generate a luminance signal and perform knee correction according to the luminance signal (hereinafter referred to as “luminance knee correction”).

  In this knee correction, for example, a video signal is processed using an approximate curve.

That is, in RGB knee correction, the slope of the approximate curve with respect to the input pixel value is KSr, KSg, KSb, the intercept is KYr, KYg, KYb, respectively, and knee correction is applied independently to each of the R, G, B color signals. If the results are R_k, G_k, and B_k, respectively, the calculation formulas are shown by the following formulas.
R_k ＝ KSr × R + KYr
G_k ＝ KSg × G + KYg
B_k = KSb × G + KYb
In this RGB knee correction, the hue of the portion subjected to knee correction is rotated, so that there is a problem that the color looks different from the portion not subjected to knee correction. That is, in RGB knee correction, knee correction is performed for each color signal, so that the color rotates with high luminance. For example, the color of a person's skin becomes yellow when RGB knee correction is performed.

  On the other hand, in the luminance knee correction, since the knee correction is performed on the luminance signal, the rotation of the color can be suppressed, but there is a disadvantage that the color disappears in the high luminance region due to the influence of the saturation diaphragm performed simultaneously. .

  In view of such a problem, for example, in Patent Document 1, in order to improve coloring at high luminance in luminance knee correction, a function for suppressing fading is mounted on the saturation stop.

JP 2006-148368 A

  However, the above-described conventional technique has a problem that unnaturalness may remain in the appearance, such as how the color remains different depending on the color.

  The present invention improves the coloring of the portion where the dynamic range compression processing using the luminance signal has been performed with a small increase in the number of circuits, prevents fast fading, and moves the color remaining processing in the high luminance region in luminance knee correction depending on the pattern. It is an object to make an optimal adjustment so as not to leave an unnatural appearance.

  The video signal processing apparatus according to the first aspect of the present invention performs knee correction on the luminance component extracted from the input video signal, and the color density in the high luminance portion is calculated from the original signal. Luminance knee correction means for adjustment based on the above is provided.

  Therefore, the brightness knee correction means can obtain a natural color with less color around the high brightness portion.

  In this first aspect, the color density is the saturation calculated from the original signal, and the luminance knee correction means calculates the coloring in the high luminance portion from the original signal when performing knee correction on the luminance. It may be adjusted according to the saturation level. Alternatively, in this first aspect, the color density is the level of the color difference signal calculated from the original signal, and the luminance knee correction means adds color in the high luminance part when performing knee correction on the luminance. It may be adjusted according to the level of the color difference signal calculated from the original signal.

  A video signal processing apparatus according to a second aspect of the present invention includes a luminance signal generating unit that extracts a luminance signal from an input video signal, a subtracting unit that subtracts the luminance signal from each color signal of the video signal, and a video signal A composite luminance signal is calculated on the basis of a signal calculated based on the maximum value of each color signal of the video signal after low-pass filtering and a predetermined first coefficient. A first correction coefficient is calculated by dividing the corrected signal by the combined luminance signal, and the signal calculated based on the first correction coefficient and the maximum value and the saturation level of the color signal are calculated. A second correction coefficient for preventing fading is calculated based on the second coefficient, and knee correction is performed on the luminance signal calculated by the luminance signal generation unit using at least the first and second correction coefficients. Carry out Comprising calculation means adds the luminance signal knee correction has been performed and the output of the subtraction means, and an adding means for outputting a video signal knee correction has been performed.

  Accordingly, knee correction is performed only on the luminance signal by the calculation means, and a natural color with less color rotation is obtained in the high luminance portion, and adjustment is performed so that the appearance becomes natural.

  In the second aspect, the calculation means may perform the knee correction by further using a third correction coefficient for making the saturation remaining processing variable according to the saturation level. Alternatively, in the second aspect, the calculation means may perform the knee correction by further using a fourth correction coefficient for making the saturation remaining processing variable according to the level of the color difference signal.

  An imaging apparatus according to a third aspect of the present invention includes an imaging unit that captures a subject image and outputs an imaging signal, a signal processing unit that outputs a video signal obtained by performing predetermined processing on the imaging signal, and the video signal Luminance signal generating means for extracting the luminance signal from the subtracting means for subtracting the luminance signal from each color signal of the video signal, based on the maximum value of each color signal of the video signal after low-pass filtering the video signal A combined luminance signal is calculated based on the calculated signal and a predetermined first coefficient, and a signal obtained by performing knee correction on the combined luminance signal is divided by the combined luminance signal to obtain the first A correction coefficient is calculated, and a second correction coefficient for preventing fading based on the first correction coefficient, a signal calculated based on the maximum value, and a second coefficient related to the saturation level of the color signal is calculated. Calculate and shine An arithmetic unit that performs knee correction on the luminance signal calculated by the signal generation unit using at least the first and second correction coefficients, a luminance signal on which the knee correction has been performed, and an output of the subtracting unit, And adding means for outputting a video signal subjected to knee correction.

  Accordingly, knee correction is performed only on the luminance signal in the video signal obtained by performing predetermined processing such as A / D conversion on the imaging signal obtained by the imaging means, thereby obtaining a high-luminance portion. In this way, natural colors with few colors are obtained, and adjustments are made so that the appearance is natural.

  A video signal processing method according to a fourth aspect of the present invention includes a step of extracting a luminance signal from an input video signal, a step of subtracting the luminance signal from each color signal of the video signal, and after low-pass filtering the video signal A signal obtained by calculating a composite luminance signal based on a signal calculated based on the maximum value of each color signal of the video signal and a predetermined first coefficient, and applying knee correction to the composite luminance signal Is divided by the combined luminance signal, a first correction coefficient is calculated, and the first correction coefficient, the signal calculated based on the maximum value, and the second coefficient related to the saturation level of the color signal are calculated. Calculating a second correction coefficient for preventing color fading based on the first correction coefficient, and performing knee correction on the luminance signal calculated by the luminance signal generation means using at least the first and second correction coefficients; The knee correction is the sum of the output after luminance signal and the subtraction performed, comprising a step of outputting a video signal knee correction has been performed.

  Therefore, knee correction is performed only on the luminance signal, and a natural color with little color rotation is obtained in the high luminance portion, and adjustment is performed so that the appearance is natural.

  According to the present invention, by adding a small number of circuits, coloring of a portion subjected to dynamic range compression processing using a luminance signal is improved, fast fading is prevented, and high-luminance color-remaining processing is performed with luminance knee correction. Thus, it is possible to provide a video signal processing device, an imaging device, and a video signal processing method that can be changed dynamically and can be optimally adjusted so as not to leave unnaturalness in appearance.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, a best mode for carrying out the invention (hereinafter simply referred to as an embodiment) will be described in detail with reference to the drawings.

  FIG. 1 shows and describes the configuration of a video signal processing apparatus according to an embodiment of the present invention.

  As shown in FIG. 1, the video signal processing apparatus includes a luminance knee correction circuit 1 and a saturation diaphragm circuit 2. In such a configuration, when color signals of R (Red), G (Green), and B (Blue) are input to the luminance knee correction circuit, luminance knee correction as will be described in detail later is performed. R, G, B signals R_yk, G_yk, B_yk after luminance knee correction are output. These signals R_yk, G_yk, B_yk are input to the saturation diaphragm circuit 2 and subjected to a saturation diaphragm process, which will be described in detail later. As a result, R, G, B signals R_ys, G_ys, B_ys after the saturation diaphragm process are performed. Is output.

  The detailed configuration of the luminance knee correction circuit 1 is shown in FIG.

  That is, as shown in FIG. 2, the luminance knee correction circuit 1 includes a luminance generation unit 11, low-pass filters (LPFs) 12, 13, a Y / MANY generation unit 14, a subtraction unit 15, and a coefficient generation unit. 16, a Sat generator 17, a calculator 18, and an adder 19.

  In such a configuration, the luminance knee correction employed in the present embodiment performs processing that suppresses color fading and suppresses fading and leaves saturation while preventing color rotation.

  That is, the R, G, B color signals are input to the luminance generation unit 11, the luminance components are extracted by the luminance generation unit 11, and the luminance signal Y is generated. The luminance signal Y is input to the subtractor 15 and is also input to the Y / NAMY generator 14 after the low frequency component is removed by the LPF 12.

  The R, G, B color signals are also input to the Y / NAMY generator 14 after the low frequency components are removed by the LPF 12. The Y / NAMY generator 14 generates a signal NAMY that is the maximum value of the R, G, B color signals, and sends the luminance signal Y and the signal NAMY to the coefficient generator 16.

The coefficient generation unit 16 obtains a combined luminance signal Mix_Y from the signal NAMY obtained by the maximum value of the input color signal and the luminance signal Y using a predetermined coefficient KNAM according to the following equation.
Mix_Y = Y + KNAM × (NAMY−Y)
Here, if the slope of the approximate curve is KS, the intercept is KY, Mix_Y is knee-corrected, and the luminance value after knee correction is Y_yk,
Y_yk ＝ KS × Mix_Y + KY
Is established.

Accordingly, the correction coefficient Kw (first correction coefficient) for luminance knee correction is obtained by dividing the luminance value Y_yk by the combined luminance signal Mix_Y.
Kw = Y_yk / Mix_Y
It becomes.

  On the other hand, in order to prevent fading, a coefficient Kw ′ (second correction coefficient) is obtained by the following equation.

  Here, CHMAX is a saturation level at the color signal level.

  The coefficient generator 16 sends the coefficients Kw and Kw ′ thus calculated to the calculator 18.

  In the present embodiment, the luminance knee correction is applied only to the luminance component.

That is, the calculation unit 18 calculates the coefficient Kw, Kw ′, the luminance signal Y, and the signal Y ′ subjected to the luminance knee correction based on the predetermined coefficient KADJ by the following equation.
Y ′ = [{KADJ × (Kw−Kw ′) + Kw ′} × Y]
Here, KADJ is a coefficient that takes a value between 0 and 1, and when it is 0, the cost for preventing fading is greatest. By doing so, it is possible to improve coloring in a high luminance region while reducing multiplication operations.

This signal Y ′ is input to the adder 19, and the adder 19 outputs an output signal after luminance knee correction based on the color difference signals RY, GY, BY generated by the subtractor 15 and the signal Y ′. R_yk, G_yk, B_yk are obtained by the following equations.
R_yk = Y '+ (RY)
G_yk = Y '+ (GY)
B_yk ＝ Y '＋ (BY)
On the other hand, there is a problem that the process of leaving the saturation to prevent fading is unnatural.

  For example, a portion that has a three-dimensional appearance due to various gradations due to lighting or the like eliminates a difference in gradation by performing a process of leaving saturation, and becomes a uniform color.

  As a result, there is a problem that it looks like a painting.

  In order to solve this problem, a process for making the process of leaving the saturation variable according to the saturation level of the signal is further added. When the saturation remaining processing is made linear by the coefficient Sat (third correction coefficient) generated by the Sat generator 18, the knee correction is expressed by the following equation.

  In this case, as the coefficient Sat is closer to 0, normal luminance knee correction processing is performed, and conversely, as Sat is closer to 1, saturation remaining processing is performed.

  By changing the range and slope of the coefficient Sat in this equation in various ways, it is possible to adjust the coloring due to the saturation. In the example, a system that reacts linearly to saturation is shown, but it is also possible to improve the system so as to show a non-linear response. However, in practice, the square root calculation in the saturation calculation has a very large circuit scale.

  To avoid this problem, it is conceivable to perform approximate calculations, but there is a tendency for the circuit scale to increase in order to improve accuracy in the approximate calculation. There is also the problem of getting worse.

  Therefore, it goes without saying that the level of the color difference signal may be used instead of the saturation, and similarly, the saturation remaining processing may be made variable. This is expressed by the following equation, where NAM_CY (fourth correction coefficient) is a coefficient for changing the saturation remaining processing according to the level of the color difference signal.

  In this example, the color leaving process is controlled using the maximum value of the color difference as a gain.

  By doing in this way, the effect similar to the color-remaining processing by saturation is obtained while minimizing the calculation amount. Similarly, a method that uses a simple sum or average of color differences, a method that distinguishes particularly sensitive colors by the ratio of color differences, and a method that does not perform open / close operations by saturation calculation are also conceivable. Therefore, it seems best to select an optimal correction value calculation method in consideration of human visual characteristics and the like.

  With respect to the signal obtained as described above, the saturation stop circuit 2 applies the saturation stop so that it finally falls within the saturation level set for each color signal, thereby obtaining the final luminance knee. Output is obtained. This can be shown by the following equation.

  Here, TEWC is the set saturation level.

  As described above, according to the present embodiment, the luminance generator 11 that extracts the luminance signal Y from the input video signal, and the luminance signal Y from the R, G, and B signals that are the color signals of the video signal. A subtractor 15 for subtracting the signal, a signal NAMY calculated based on the maximum value of each color signal of the video signal after the low-frequency removal of the video signal by the LPF 12, and a coefficient KNAM as a predetermined first coefficient And the combined luminance signal Mix_Y is calculated, and the signal Y_yk obtained by performing knee correction on the Mix_Y is divided by the combined luminance signal Mix_Y to calculate Kw as a first correction coefficient. A luminance signal calculated by the luminance generation unit 11 is calculated by calculating a second correction coefficient Kw ′ for preventing fading based on the correction coefficient Kw, the signal NAMY, and the second coefficient CHMAX related to the saturation level of the color signal. For Y, at least first and second correction factors Kw , Kw ′, the arithmetic unit 18 that performs knee correction, and the luminance signal subjected to knee correction and the output of the subtracting unit 15 are added, and the video signals R_yk, G_yk, B_yk subjected to knee correction are added. A video signal processing apparatus including an adding unit 19 for outputting is provided.

  Note that the calculation unit 18 may further perform the knee correction by further using a coefficient Sat as a third correction coefficient for making the saturation remaining processing variable depending on the saturation level. The calculation unit 18 may further perform the knee correction by further using a coefficient NAM_CY as a fourth correction coefficient for making the saturation remaining processing variable according to the level of the color difference signal.

  Next, FIG. 3 shows a configuration in which the video signal processing apparatus according to this embodiment is applied to an imaging apparatus. The imaging apparatus is a digital video camera or the like, and includes a lens unit 100, an imaging device 101, an analog processing and AD conversion unit 102, a defect correction unit 103, a camera signal processing unit 104, a frame processing unit 105, a correction unit 106, And an output unit 107. The video signal processing apparatus is mounted as a part of the correction unit 106.

  In such a configuration, the lens unit 100 includes a focus lens, a zoom lens, a diaphragm blade, and the like, and a drive unit that drives these lenses and the like. The subject image incident through the lens unit 100 is received by the image sensor 101, subjected to photoelectric conversion, and an image signal is output. The image sensor 101 is a solid-state image sensor such as a C-MOS image sensor or a CCD image sensor. The imaging signal is supplied to the analog processing and A / D conversion unit 102, subjected to analog processing such as clamping and amplification processing, and digitized by A / D conversion.

  The defect correction unit 103 is a circuit that corrects an imaging signal of a defective portion when a defect has occurred in a pixel of the image sensor 101. The imaging signal that has been subjected to the defect correction processing by the defect correction unit 103 is supplied to the camera signal processing unit 104 and subjected to processing such as white balance processing, aberration correction processing, and shading processing. The image signal subjected to these processes is supplied to the frame processing unit 105, and the image signal is subjected to frame (field) unit processing.

  Then, the imaging signal that has been processed in units of frames (fields) is supplied to the correction unit 106. In the correction unit 106, the luminance knee correction as described above is performed on the luminance signal and supplied to the output unit 107. Thus, the output unit 107 converts the input imaging signal into a signal corresponding to a predetermined video format, and outputs the signal to the outside.

  As described above in detail, according to an embodiment of the present invention, it is possible to improve coloring of a portion subjected to dynamic range compression processing using a luminance signal. Furthermore, it is possible to prevent fast fading with a small increase in circuit. Further, it is possible to dynamically change the color-remaining process in the high luminance area in the luminance knee correction depending on the pattern. In addition, it is possible to dynamically change the high-luminance color-remaining process with a smaller circuit scale according to the pattern.

  The embodiment of the present invention has been described above, but the present invention is not limited to this, and it is needless to say that various improvements and changes can be made without departing from the spirit of the present invention.

1 is a configuration diagram of a video signal processing apparatus according to an embodiment of the present invention. The detailed block diagram of the brightness | luminance knee correction circuit of a video signal processing apparatus. The block diagram of the imaging device to which the video signal processing apparatus which concerns on this Embodiment is applied.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Luminance knee correction circuit, 2 ... Saturation stop circuit, 11 ... Luminance production | generation part, 12 ... LPF, 13 ... LPF, 14 ... Y / NAMY production | generation part, 15 ... Subtraction part, 16 ... Coefficient production | generation part, 17 ... Sat Generation unit, 18 ... calculation unit, 19 ... addition unit

Claims (8)

In the video signal processing device,
A knee correction is performed on the luminance component extracted from the input video signal, and luminance knee correction means for adjusting the coloring in the high luminance portion based on the color density calculated from the original signal is provided. A video signal processing apparatus. The color density is the saturation calculated from the original signal,
2. The video signal according to claim 1, wherein the luminance knee correction unit adjusts coloring in a high luminance portion according to a saturation level calculated from an original signal when performing knee correction on luminance. Processing equipment. The color density is the level of the color difference signal calculated from the original signal,
2. The video signal according to claim 1, wherein the luminance knee correction means adjusts coloring in a high luminance portion according to a level of a color difference signal calculated from an original signal when performing knee correction on luminance. Processing equipment. Luminance signal generating means for extracting a luminance signal from the input video signal;
Subtracting means for subtracting the luminance signal from each color signal of the video signal;
A composite luminance signal is calculated based on a signal calculated based on the maximum value of each color signal of the video signal after low-pass filtering the video signal and a predetermined first coefficient, and the composite luminance signal A first correction coefficient is calculated by dividing the signal subjected to knee correction by the combined luminance signal, and the signal calculated based on the first correction coefficient and the maximum value and the saturation of the color signal are calculated. A second correction coefficient for preventing fading is calculated based on the second coefficient relating to the level, and at least the first and second correction coefficients are applied to the luminance signal calculated by the luminance signal generating means. Computing means for performing knee correction using,
A video signal processing apparatus comprising: an addition unit that adds the luminance signal subjected to the knee correction and the output of the subtraction unit and outputs a video signal subjected to the knee correction. 5. The video signal processing according to claim 4, wherein the arithmetic means further performs the knee correction by further using a third correction coefficient for making the saturation remaining processing variable according to the saturation level. apparatus. 5. The video signal processing according to claim 4, wherein the arithmetic means further performs the knee correction by further using a fourth correction coefficient for making the saturation remaining processing variable according to the level of the color difference signal. apparatus. Imaging means for capturing a subject image and outputting an imaging signal;
Signal processing means for outputting a video signal obtained by performing predetermined processing on the imaging signal;
Luminance signal generating means for extracting a luminance signal from the video signal;
Subtracting means for subtracting the luminance signal from each color signal of the video signal;
A composite luminance signal is calculated based on a signal calculated based on the maximum value of each color signal of the video signal after low-pass filtering the video signal and a predetermined first coefficient, and the composite luminance signal A first correction coefficient is calculated by dividing the signal subjected to knee correction by the combined luminance signal, and the signal calculated based on the first correction coefficient and the maximum value and the saturation of the color signal are calculated. A second correction coefficient for preventing fading is calculated based on the second coefficient relating to the level, and at least the first and second correction coefficients are applied to the luminance signal calculated by the luminance signal generating means. Computing means for performing knee correction using,
An image pickup apparatus comprising: an addition unit that adds the luminance signal subjected to the knee correction and the output of the subtraction unit and outputs a video signal subjected to the knee correction. Extracting a luminance signal from the input video signal;
Subtracting the luminance signal from each color signal of the video signal;
A composite luminance signal is calculated based on a signal calculated based on the maximum value of each color signal of the video signal after low-pass filtering the video signal and a predetermined first coefficient, and the composite luminance signal A first correction coefficient is calculated by dividing the signal subjected to knee correction by the combined luminance signal, and the signal calculated based on the first correction coefficient and the maximum value and the saturation of the color signal are calculated. A second correction coefficient for preventing fading is calculated based on the second coefficient relating to the level, and at least the first and second correction coefficients are applied to the luminance signal calculated by the luminance signal generating means. Using to perform knee correction,
A video signal processing method comprising: adding the luminance signal subjected to the knee correction and the output after the subtraction to output a video signal subjected to the knee correction.

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