JP2000149014A - Image processor and image processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct gradation by efficiently preventing partial lowering of contrast by deciding an area to which inputted image data belong and correcting the signal level of the image data based on the decision result. SOLUTION: An image pickup result VN of normal exposure by electric charge storage time set by a user and an image pickup result VS of shot time exposure by short electric charge storage time are outputted alternately, and an image pickup result VT is generated by being composited by a level correcting circuit 6 and an adding circuit 5. A low-frequency component r(i, j) as an average value of pixel values is detected, fine structure in an image is removed and an area with a flat pixel value is extracted by an area deciding filter 10. A contrast correction coefficient g(i, j) is generated, depending on a signal level of the low frequency component r(i, j) by a coefficient calculating circuit 11, and thus the pixel value is corrected by a multiplying circuit 12, the pixel value is corrected and outputted by a gain according to each area based on the low-frequency component r(i, j).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an image processing apparatus and an image processing method, and can be applied to, for example, an image processing apparatus such as a television receiver, a video tape recorder, a television camera, and a printer. According to the present invention, for example, a region to which image data belongs is determined based on a low-frequency component of a pixel value, and a signal level of image data is corrected based on the determination result, thereby effectively reducing partial contrast deterioration. It is possible to correct the gradation by avoiding it.

[0002]

2. Description of the Related Art Conventionally, in an image processing apparatus such as a television camera, the gradation of image data obtained through image input means such as an image pickup means is corrected and output.

FIG. 15 is a characteristic curve diagram showing input / output characteristics of a signal processing circuit applied to the gradation correction processing. This type of signal processing circuit reduces the gain when the input level 1 rises above a predetermined reference level lk. As a result, this type of signal processing circuit suppresses the signal level when the input level becomes higher than the reference level lk and outputs the signal. In this case, the gradation is corrected at the expense of the contrast of the portion where the signal level is high. ing.

In the characteristic curve diagram shown in FIG. 15, the horizontal axis represents a pixel value 1 which is an input level of image data.
The vertical axis represents the pixel value T (l), which is the output level of the image data, and Lmax represents the maximum level that each pixel of the input / output image can take. In the following, a function indicating an input / output relationship as shown in the characteristic curve diagram is referred to as a level conversion function.

FIG. 16 is a characteristic curve diagram showing the input / output characteristics of the same type of signal processing circuit. The signal processing circuit using the level conversion function reduces the gain when the input level 1 is equal to or lower than the first reference level ls and when the input level l is equal to or higher than the second reference level lb. As a result, this signal processing circuit corrects the gradation at the expense of the contrast between the low and high signal levels.

On the other hand, in image processing using a computer, gradation is corrected by, for example, histogram equalization.

This histogram equalization is:
This is a method of adaptively changing the level conversion function according to the frequency distribution of the pixel values of the input image, and is a method of correcting the gray levels by reducing the gray levels of a portion having a low frequency distribution of the pixel values.

That is, as shown in FIG. 17, in the histogram equalization process, the frequency distribution H which is the total of the number of pixels based on the pixel value 1 of the input image is used.
Based on (l), a cumulative frequency distribution C (l) is detected by the following equation.

[0009]

(Equation 1)

In the process of histogram equalization, the cumulative frequency distribution C
The level conversion function T (l) is defined by normalizing (l) by the following equation, and the signal level of the input image is corrected according to the level conversion function T (l). Here, Fmax is the final value of the cumulative frequency distribution C (l), and Lmax is the maximum value of the input / output level.

[0011]

(Equation 2)

[0012] Such a process of correcting the gradation may be performed even when the image data is transmitted through a transmission line, displayed on a display device, or stored in a storage device.
It is appropriately executed as needed for the purpose of suppressing the dynamic range.

[0013]

In the tone correction processing according to the above-described conventional method, the entire tone is corrected at the expense of the contrast of any part. This is because, in any of the methods, in order to avoid generation of an unnatural image, level conversion is performed using an input / output function having a monotonically increasing property.

Therefore, in the case of the conventional method, there is a problem that the contrast is partially reduced in the processed image.

The present invention has been made in view of the above points, and it is an object of the present invention to propose an image processing apparatus and an image processing method capable of correcting gradation by effectively avoiding a partial decrease in contrast. Things.

[0016]

According to the present invention, there is provided an image processing apparatus or an image processing method, wherein an area to which image data belongs is determined, and a pixel value of the image data is determined based on the determination result. Is generated, and the pixel value of the image data is corrected according to the correction coefficient.

A region to which the image data belongs is determined, a correction coefficient for correcting the pixel value of the image data is generated based on the determination result, and the pixel value of the image data is corrected according to the correction coefficient. Then, the pixel values can be corrected by the same coefficient to maintain the magnitude relation of the pixel values in the area, and the magnitude relation of the pixel values can be reversed between the pixels belonging to different areas, thereby reducing the partial contrast deterioration. It is possible to correct the entire gradation by avoiding it.

[0018]

Embodiments of the present invention will be described below in detail with reference to the drawings.

(1) First Embodiment (1-1) Configuration of First Embodiment FIG. 1 is a block diagram showing a television camera according to a first embodiment of the present invention. In the television camera 1, a CCD solid-state imaging device (CCD) 2 outputs an imaging result by driving a timing generator (TG) 3. At this time, the CCD solid-state imaging device 2 obtains an imaging result at a period of 1/60 [sec] according to the charge accumulation time set by the user, and outputs the imaging result as an imaging result VN by normal exposure. In addition, CCD solid-state imaging device 2
In the vertical blanking period of the imaging result VN obtained by the normal exposure, an imaging result obtained by a charge accumulation time shorter than the charge accumulation time obtained by the normal exposure is obtained, and the imaging result is output as the imaging result VS of the short exposure I do.

As a result, as shown in FIG. 2, in the CCD solid-state image pickup device 2, when the amount of incident light is equal to or more than a predetermined amount of light, the image pickup result VN (FIG. 2A) by normal exposure in which the output level is saturated, The imaging result V of the short-time exposure in which the output level is not saturated due to the shorter charge accumulation time
S (FIG. 2B) is output as a set.

The memory 4N converts the image pickup result VN (converted into red, blue and green color signals) by the normal exposure through a correlated double sampling circuit, a defect correction circuit, a matrix operation circuit, an analog-to-digital conversion circuit and the like (not shown). Is input), and the imaging result VN by this normal exposure is input.
Is output temporarily.

Similarly, the memory 4S stores a correlation 2 (not shown).
The imaging result VS obtained by the short-time exposure is input via a multiple sampling circuit, a defect correction circuit, a matrix operation circuit, an analog-digital conversion circuit, and the like, and the imaging result VS obtained by the short-time exposure is temporarily held and output.

The addition circuit 5 adds the imaging result VN obtained by the normal exposure held in the memory 4N and the imaging result VS held by the short-time exposure held in the memory 4S to provide a wide dynamic range and a sufficient dynamic range. The imaging result VT based on the pixel value is output, and the level correction circuit 6 outputs the imaging result VS by the short-time exposure output from the memory 4S so that practically sufficient linearity can be secured in the imaging result VT obtained by the adding circuit 5. Is corrected and output.

As a result, the television camera 1 generates an imaging result VT (FIG. 2C) with a much larger dynamic range than in the past.

The gradation correction circuit 8 corrects the pixel value of the image pickup result VT to correct and output the gradation of the image pickup result VT. Subsequently, the signal processing circuit 9 executes various signal processing necessary for the television camera and outputs the imaging result to an external device or the like. At this time, the pixel value of the imaging result is uniformly suppressed so as to correspond to the output device. By doing so, the dynamic range of the imaging result is suppressed and output.

In this process, the tone correction circuit 8 performs the following arithmetic operation in advance to obtain the color signals R,
A luminance signal Y is generated from the imaging result VT of G and B, and the gradation of each of the color signals R, G and B is corrected based on the luminance signal Y and output.

[0027]

(Equation 3)

Here, in the gradation correction circuit 8, the area judgment filter 10 judges the area to which the image data which is the luminance signal Y belongs, and outputs the judgment result. At this time, the area determination filter 10 detects an average luminance level, which is an average value of pixel values, as a feature amount indicating a characteristic of a predetermined range in the vicinity of the image data, and thereby determines which average luminance level the image data belongs to. The determination is made, and the average value, which is the average luminance level, is output as the determination result.

That is, the area determination filter 10 is a two-dimensional low-pass filter, and has a pixel value x of the luminance signal Y in the imaging result VT sequentially input in the raster scanning order.
For (i, j), a low frequency component r (i, j) represented by the following equation is detected, and this low frequency component r
(I, j) is output as the determination result.

[0030]

(Equation 4)

In the equation (3), N and M are constants representing the size of the neighboring area for calculating the average value.
As shown in FIG. 7, in this embodiment, the horizontal direction is indicated by a suffix with a code i and the vertical direction is indicated by a suffix with a code j in the imaging results VT input in the raster scanning order. As a result, the area determination filter 10 sets the imaging result V
A region having relatively flat pixel values is extracted by removing fine structures in the image from the image based on T. Since the area determination filter 10 aims at such processing, it is desirable that the band is relatively narrow.

The coefficient calculation circuit 11 calculates the low frequency component r
According to the signal level of (i, j), for example, a contrast correction coefficient g is calculated by a coefficient calculation function G as shown in FIG.
(I, j) is generated. Here, the coefficient calculation function G is
For example, the level conversion function T (l) described above with reference to FIG.
Is a function obtained by performing an arithmetic operation on the following equation.

[0033]

(Equation 5)

Thus, the coefficient calculation circuit 11 generates and outputs a contrast correction coefficient g (i, j) by the following equation, and outputs the low-frequency component r (i,
For a region where the signal level of j) is equal to or lower than the predetermined reference level lk, a contrast correction coefficient g (i, j) based on a constant value gmax of 1 or more is output.
For the above region, the contrast correction coefficient g (i, j) is output so that the value gradually approaches the value gmin according to the signal level of the low frequency component r (i, j).

[0035]

(Equation 6)

The multiplying circuit 12 multiplies the contrast correction coefficient g (i, j) thus generated by the pixel value x (i, j) of the corresponding imaging result VT (in this case, This is a process for each color signal), and the signal level of the imaging result VT is corrected by the contrast correction coefficient g (i, j) and output.

(1-2) Operation of the First Embodiment In the above configuration, in the television camera 1 (FIG. 1), the image is captured by the CDD solid-state imaging device 2 by the normal exposure according to the charge storage time set by the user. The result VN (FIG. 2A) and the imaging result VS (FIG. 2B) of the short-time exposure with a short charge accumulation time are alternately output, and the imaging results VN and VS are stored in the memories 4N and 4S, respectively. Will be retained. In the television camera 1, the two imaging results VN and VS are combined by the level correction circuit 6 and the addition circuit 5, whereby the imaging result VT with a much larger dynamic range than in the past (FIG. 2C) ) Is generated.

In this imaging result VT, the luminance signal Y
Is generated, and the area determination filter 10 of the gradation correction circuit 8 detects an average value of pixel values, which is a feature amount indicating a feature in a predetermined range in the vicinity of the input image data, thereby indicating an area to which the input image data belongs. A determination result is generated.
More specifically, the low frequency component r (i, j), which is the average value of the pixel values, is detected by the region determination filter 10, whereby the fine structure in the image is removed, and the region where the pixel values are relatively flat is detected. Is extracted. Also, this low frequency component r
(I, j) is output as the determination result.

In the imaging result VT, a coefficient correction circuit 11 generates a contrast correction coefficient g (i, j) according to the signal level of the low frequency component r (i, j). The pixel value is corrected by the multiplying circuit 12 by (i, j), whereby the pixel value is corrected by a gain corresponding to each region based on the low frequency component r (i, j) and output.

As a result, in the imaging result VT, in a region where the signal level of the low-frequency component r (i, j) is equal, the pixel value is corrected by the same gain.
In a region where the signal level of the low frequency component r (i, j) is different, the pixel values can be made close to each other in accordance with the setting of the level conversion function T (l). It can also be reversed. As a result, the contrast in each region can be naturally increased with respect to the entire gradation, and the whole gradation can be corrected while effectively preventing a partial decrease in contrast.

That is, as shown in FIG.
Pixel value x (i, j) pulsates at a frequency equal to or higher than the cutoff frequency of the low-pass filter 10, and furthermore, the pixel value x
In the case where the DC level of (i, j) rises sharply (FIG. 5B), the change of the low frequency component r (i, j) corresponding to the rapid change of the DC level is used to calculate the coefficient. The case where the function G (l) straddles the inflection point (FIG. 5)
(A)), depending on the conventional level conversion function described above with reference to FIG. 15, the contrast is suppressed in a portion where the pixel value x (i, j) is large (FIG. 5C).

However, according to this embodiment, before and after the signal level of the low frequency component r (i, j) sharply rises, the gain according to the signal level of the low frequency component r (i, j) is obtained. The pixel value x (i, j) is corrected, and the signal level is corrected by setting the coefficient calculation function G (l). At this time, the pixel value x (i,
In a portion where j) is small, the pixel value x (i, j) is corrected by the gain gmax based on the average level l2 of the peak value l3 and the bottom value l1, so that the low-level region is comparable to the conventional method. Can be obtained (FIG. 5D).

On the other hand, on the high level side, the average level 15 of the peak value 16 and the bottom value 14 is similarly calculated.
The pixel value x (i, j) is corrected by the gain g5 by
At this time, the pixel value is corrected by the uniform gain of the peak value 16 and the bottom value 14 so that the contrast between the peak value 16 and the bottom value 14 is:
The signal is amplified by the gain g5.

Thus, in this embodiment, although the gradation when viewed as a whole does not change significantly, the microscopic pulsation is not affected by the imaging result VT as the input image.
Large pulsation due to the above can be enlarged.

As shown in FIG. 6, similarly, the pixel value x
(I, j) pulsates and the DC level rises sharply (FIG. 6 (B)), and the pixel value x (i, j)
If the pulsation is biased to a higher level than the inflection point of the coefficient calculation function G (l) (FIG. 5B), all the pixel values x may be obtained depending on the conventional level conversion function described above with reference to FIG.
The contrast is suppressed at (i, j) (FIG. 6C).

However, also in this case, on the low level side and the high level side, the average value levels l2 and l5 are respectively provided.
Are corrected by the gains g2 and g5 corresponding to
Although the gradation when viewed as a whole does not change significantly, the microscopic pulsation is not affected by the imaging result V which is the input image.
Large pulsation due to T can be expanded.

(1-3) Effect of First Embodiment According to the above configuration, a region to which image data belongs is determined, and a correction coefficient for correcting a pixel value of the image data is generated based on the determination result. In addition, by correcting the pixel value of the image data according to the correction coefficient, the same coefficient holds the magnitude relation of the pixel values within the same area while maintaining the same value.
Pixel values of pixels belonging to different regions can be made closer to each other as necessary, and can be reversed in extreme cases. As a result, the contrast in each area can be enlarged within a predetermined level range, and the entire gradation can be corrected while avoiding a partial decrease in contrast.

At this time, by using a low-frequency component by a low-pass filter as a feature value and correcting the pixel value with reference to the low-frequency component, partial reduction in contrast can be avoided with a simple configuration. Thus, the entire gradation can be corrected.

(2) Second Embodiment FIG. 7 is a block diagram showing a gradation correction circuit applied to a television camera according to a second embodiment of the present invention. This gradation correction circuit 28 is applied instead of the gradation correction circuit 8 described above with reference to FIG.

Here, the quantization circuit 29 requantizes the pixel value of the luminance signal Y constituting the imaging result VT, thereby reducing the number of bits and outputting the result. In this embodiment, the quantization circuit 29 performs the following arithmetic operation on the pixel value x (i, j) by a preset quantization step Q, thereby obtaining the pixel value x (i , J) is subjected to a linear quantization process to output a pixel value x ′ (i, j). Here, int (a) is a function for rounding down the decimal part of a.

[0051]

(Equation 7)

The area determination filter 30 is formed in the same manner as the area determination filter 10 according to the first embodiment except that the number of bits is different.

The look-up table (LUT) 31 is
The coefficient calculation circuit according to the first embodiment is configured, and the low frequency component r (i, i,
The correction coefficient g (i, j) is output using j) as an address. Thus, the lookup table 31 stores the correction coefficient LUT (i) represented by the following equation at the ith address.

[0054]

(Equation 8)

According to the above configuration, the same effect as in the first embodiment can be obtained even if the pixel values are quantized and processed in advance. In addition, by generating the correction coefficient by using the look-up table, the entire process can be simplified by that much, and the configuration of the region determination filter can be simplified by performing quantization in advance at this time. Can reduce the size of the lookup table.

(3) Third Embodiment FIG. 8 is a block diagram showing a gradation correction circuit applied to a television camera according to a third embodiment of the present invention. This gradation correction circuit 38 is applied instead of the gradation correction circuit 28 described above with reference to FIG.
A lookup table 41 and an interpolation circuit 42 are arranged in place of the lookup table 31 of FIG.

Here, the lookup table 41 has an address smaller than the number of levels that the output value r (i, j) of the area determination filter 30 can take, and the output value r (i, j)
, Two addresses addr0 (i, j), ad expressed by the following equation
dr1 (i, j) and correction coefficients g0 (i, j), g1
(I, j). Here, the lookup table 41 outputs the two addresses addr0 (i, j) by omitting the lower bits of the output value r (i, j) of the area determination filter 30 and outputting the address addr1 (i, j). i, j), this address ad
By adding a logical 1 bit to the least significant bit of dr0 (i, j), these addresses addr0 (i, j),
addr1 (i, j) is generated and output. Here, Rmax is the maximum value that the output value x (i, j) of the area determination filter 30 can take, and R′max is the maximum value that the address of the lookup table 41 can take.

[0058]

(Equation 9)

The interpolation circuit 42 is provided for the lookup table 4
Address addr0 (i, j), ad input from 1
dr1 (i, j), correction coefficient g0 (i, j), g1
Using (i, j), an interpolation operation is performed by the following equation.
The result of the interpolation is output as a correction coefficient g (i, j).

[0060]

(Equation 10)

According to the configuration shown in FIG. 8, by generating a correction coefficient by performing an interpolation operation, it is possible to generate a correction coefficient whose value changes smoothly using a small-scale look-up table. The gradation can be corrected with minute accuracy.

(4) Fourth Embodiment FIG. 9 is a block diagram showing a gradation correction circuit applied to a television camera according to a fourth embodiment of the present invention. This gradation correction circuit 48 is applied instead of the gradation correction circuit 8 described above with reference to FIG.

In the gradation correction circuit 48, the area judgment filter 50 judges the judgment results r0 (i, j) and r1 (i, i) of the area to which the input image data with different resolutions belong.
j), r2 (i, j),..., rN−1 (i, j), and the low-pass filter unit 50A, and the determination results r0 (i, j), r1 (i, j), r
2 (i, j),..., RN-1 (i, j),
A signal synthesis unit 50B that generates a determination result r (i, j) that is a synthesized signal.

The low-pass filter section 50A includes low-pass filters (LPF) F0 and FP having different pass bandwidths.
, FN-1, and low-pass filters (LPF) F0, F1, F2,..., FN-1
The pixel value x of the luminance signal Y generated from the imaging result VT
(I, j) is input, and the corresponding low frequency components are determined as determination results r0 (i, j), r1 (i, j), r2 (i, j),.
.., RN−1 (i, j).

The signal synthesizing unit 50B includes a multiplying circuit M
0, M1, M2,..., MN−1, the determination result r
0 (i, j), r1 (i, j), r2 (i, j), ...
.., RN-1 (i, j) are weighted, and then added
3 and the result is a decision result r which is a composite signal of 1
(I, j) is generated and output. At this time, the weighting coefficients w0, w1, w2,..., WN−1 in the multiplication circuits M0, M1, M2,..., MN−1 are set in advance so as to satisfy the following relational expression. You.

[0066]

[Equation 11]

Thus, in this embodiment, by setting the weighting coefficients w0, w1, w2,..., WN-1, the contour in the imaging result VT is not abnormally emphasized.

That is, as shown in FIG.
When (i, j) changes rapidly (FIG. 10
(A)), in the low frequency component r (i, j), the signal level changes as if the sudden change in the pixel value was mitigated. In the case where the signal level of the low frequency component r (i, j) is biased to a higher level than the inflection point described above with reference to FIG. 4, the output signal of the low-pass filter is simply used as in the first embodiment. Since the correction coefficient g (i, j) is generated, immediately before the pixel value x (i, j) changes abruptly, the pixel value is amplified by an extra gain, and the pixel value x (i, j) rapidly increases. Immediately after the change, the pixel value is amplified with a small gain, whereby an output value y (i, j) (FIG. 10B) with an abnormally emphasized contour is obtained.

In this case, the pixel value of such an outline can be corrected with a substantially uniform gain to reduce the emphasis of an abnormal outline.

In this embodiment, a correction coefficient is generated from low-frequency components of a plurality of systems, thereby effectively avoiding the emphasis of abnormal contours and obtaining the same effect as in the first embodiment. It has been made possible.

According to the configuration shown in FIG. 9, by generating a correction coefficient from low-frequency components of a plurality of systems, an effect similar to that of the first embodiment can be obtained by effectively avoiding the emphasis of an abnormal contour. be able to.

(5) Fifth Embodiment FIG. 11 is a block diagram showing a gradation correction circuit applied to a television camera according to a fifth embodiment of the present invention. This gradation correction circuit 58 is applied instead of the gradation correction circuit 8 described above with reference to FIG.

In the gradation correction circuit 58, the area determination filter 60 determines the determination result r0 at a different resolution.
(I, j), r1 (i, j), r2 (i, j),.
Output rN-1 (i, j). That is, the area determination filter 60 is composed of low-pass filters (LPF) F0, F1, F2,..., FN-1 having different pass bandwidths, respectively.
, FN-1, the pixel value x (i, j) is input, and the corresponding low frequency component is determined as a determination result r0 (i, j),
r1 (i, j), r2 (i, j),..., rN-1
Output as (i, j).

The coefficient calculation circuit 61 determines the judgment result r0 (i,
j), r1 (i, j), r2 (i, j),..., rN−
Correction coefficients g0 (i, j), g corresponding to 1 (i, j)
1 (i, j), g2 (i, j),..., GN−1 (i,
j) for generating the correction coefficients g0 (i, j), g1 (i, j), g2 (i, j),.
.., GN-1 (i, j) are combined to obtain a correction coefficient g of 1
And a coefficient synthesis unit 61B for generating (i, j).

Among them, the coefficient generation section 61A performs predetermined coefficient calculation functions Gk (k = 0, 1, 2,..., N-
1), the determination results r0 (i, j), r1 (i,
j), r2 (i, j),..., rN-1 (i, j), and corresponding correction coefficients g0 (i, j), g1 (i, j), g
2 (i, j),..., GN−1 (i, j). The coefficient calculators L0, L1, L2,.

On the other hand, the coefficient synthesizing section 61B uses the multiplication circuits M0, M1, M2,..., MN-1 to correct the correction coefficients g0 (i, j), g1 (i, j), g2 (i,
j),..., gN-1 (i, j) are weighted and then added by an adding circuit 63, whereby a correction coefficient g (i, i, 1) of 1 is obtained.
j) is generated and output. At this time, the multiplication circuit M
, MN−1, w0, w1, w2,..., WN−1 are set in advance so as to satisfy the above-described relational expression (11). .

According to the configuration shown in FIG. 11, the same effect as in the fourth embodiment can be obtained by generating one correction coefficient after each of the correction coefficients is generated from the low frequency components of a plurality of systems. Obtainable.

(6) Other Embodiments In each of the above-described embodiments, a case has been described in which correction coefficients are basically generated based on the characteristics described above with reference to FIG. 4, but the present invention is not limited to this. Instead, a correction coefficient may be generated based on various input / output characteristics.
As shown in (1), a level conversion function based on input / output characteristics such that the output level decreases on the way with an increase in the input level may be used.

That is, in the conventional method, when such a function is used, since this function is not a monotonically increasing function, a pseudo contour may be generated in an image as a processing result. However, when processing is performed by dividing into regions by a low-pass filter as in the above-described embodiment, pixel values in which the magnitude relationship of pixel values is reversed in a neighboring region having a size corresponding to the pass band of the low-pass filter. Can be prevented from changing greatly. As a result, generation of a false contour can be effectively avoided.

Further, in the above-described embodiment, the case where the coefficient calculation function G is generated by the calculation processing of the equation (6) using the level conversion function T has been described. The coefficient calculation function G may be arbitrarily set without using the function T.

Further, in the above-described embodiment, the case has been described where the gradation is corrected by the gradation correction circuit and then the dynamic range is suppressed by the subsequent signal processing circuit. These processes can be collectively executed by setting a function T and a coefficient calculation function G corresponding thereto.

That is, in the process of suppressing the dynamic range, it is required that the number of bits of the output pixel value is smaller than the number of bits of the input pixel value. Is set to the maximum value allowed for the output image, and the coefficient calculation function G is generated using the maximum value, whereby these processes can be executed collectively.

When the coefficient calculation function G is arbitrarily set without using the level conversion function T, the coefficient calculation function G may be set so as to satisfy the following equation. Here, l
Represents the input pixel level, Lmax represents the maximum value of the input pixel level, and L0max represents the maximum value of the output pixel level.

[0084]

(Equation 12)

In the above embodiment, the case where the quantization circuit, the look-up table, and the interpolation circuit are used in the second and third embodiments has been described. However, the present invention is not limited to this. If necessary, all or any of these quantization circuits, look-up tables, and interpolation circuits can be applied to other than the second and third embodiments.

On the contrary, in the second and third embodiments, the quantization circuit may be omitted if necessary.

In the above embodiment, the case where a luminance signal is generated from a color signal and the gradation of the color signal is corrected based on the luminance signal has been described. However, the present invention is not limited to this. For example, when processing an imaging result (FIG. 14) in which an amplitude-modulated color signal is superimposed on a luminance signal output from a single-chip solid-state imaging device by setting a color filter as shown in FIG. The present invention can be widely applied to processing a video signal based on a color difference signal, and further to processing a composite video signal in which a chroma signal is superimposed on a luminance signal.

For example, when processing an imaging result in which a color signal whose amplitude is modulated is superimposed on a luminance signal, the color noise is reduced by setting the resolution of the correction coefficient lower than the modulation frequency of the color signal. The gradation can be corrected by avoiding it effectively.

When processing a video signal based on a luminance signal and a chrominance signal, a correction coefficient is calculated based on the luminance signal, and the gradation of the luminance signal and the chrominance signal is corrected using the correction coefficient. Of the video signal can be corrected.

In the above-described embodiment, the case where the area to which the input image data belongs is determined by the low-pass filter, and the low-frequency component output from the low-pass filter is used as the determination result. For example, in an image to be processed, for example, the similarity between an arbitrarily selected pixel and a neighboring pixel surrounding the pixel is grasped as a feature amount, and the area is sequentially enlarged from this pixel to divide the image to be processed into regions. At the same time, when the feature amount is used as a determination result or the like, the image to be processed is divided into regions by various processing methods, and the same effect as in the above-described embodiment can be obtained.

Further, in the above-described embodiment, the case where the present invention is applied to a television camera has been described. However, the present invention is not limited to this, and various images such as a television receiver, a video tape recorder, and a printer may be used. It can be widely applied to processing equipment.

[0092]

As described above, according to the present invention, an area to which input image data belongs is determined based on, for example, a low-frequency component of a pixel value, and the signal level of the image data is corrected based on the determination result. This makes it possible to correct gradation while effectively avoiding a partial decrease in contrast.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a television camera according to a first embodiment of the present invention.

FIG. 2 is a characteristic curve diagram for describing processing of an imaging result in the television camera of FIG. 1;

FIG. 3 is a schematic diagram illustrating an array of pixel values in the television camera of FIG. 1;

FIG. 4 is a characteristic curve diagram for explaining a contrast correction coefficient g (i, j).

FIG. 5 is a signal waveform chart for describing processing of a gradation correction circuit in the television camera of FIG. 1;

FIG. 6 is a signal waveform diagram for explaining processing of a gradation correction circuit at an input level different from that in FIG. 5;

FIG. 7 is a block diagram showing a gradation correction circuit applied to a television camera according to a second embodiment of the present invention.

FIG. 8 is a block diagram showing a gradation correction circuit applied to a television camera according to a third embodiment of the present invention.

FIG. 9 is a block diagram showing a gradation correction circuit applied to a television camera according to a fourth embodiment of the present invention.

FIG. 10 is a signal waveform diagram for explaining the operation of the gradation correction circuit of FIG. 9;

FIG. 11 is a block diagram showing a gradation correction circuit applied to a television camera according to a fifth embodiment of the present invention.

FIG. 12 is a characteristic curve diagram for explaining a level conversion function applied to a gradation correction circuit according to another embodiment.

FIG. 13 is a plan view for describing a color filter.

14 is a signal waveform diagram showing an imaging result when the color filter of FIG. 13 is used.

FIG. 15 is a characteristic curve diagram for explaining a level conversion function applied to a conventional dynamic range suppression process.

FIG. 16 is a characteristic curve diagram for explaining a level conversion function applied to a dynamic range suppression process according to another example different from FIG.

FIG. 17 is a characteristic curve diagram for explaining a histogram equalization process.

[Explanation of symbols]

1 ... television camera, 8, 28, 38, 48, 5
8: gradation correction circuit, 10, 30, 50, 60 ... area determination filter, 11, 61 ... coefficient calculation circuit, 12, M
0 to MN-1 multiplication circuit, 29 quantization circuit, 3
1, 41 ... Look-up table, F0 to FN-1 ...
... low-pass filter, 53, 63 ... addition circuit, L0
LN-1: coefficient calculating unit

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[Procedure amendment]

[Submission Date] March 3, 2000 (200.3.3)

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Kazuhiko Ueda 6-35 Kita Shinagawa, Shinagawa-ku, Tokyo F-term in Sony Corporation (reference) 5B057 AA11 BA28 CA01 CA08 CA12 CA16 CB01 CB08 CB12 CB16 CC02 CE06 CE08 CE11 CE16 CH09 CH11 DB06 5C077 MP08 PP01 PP15 PP27 PP28 PP48 PQ18 RR18 TT09

Claims (30)

[Claims] 1. An image processing apparatus for correcting the gradation of image data, wherein: an area determination unit that determines an area to which the image data belongs and outputs a determination result; and a pixel of the image data based on the determination result. An image processing apparatus comprising: a coefficient calculation unit that outputs a correction coefficient for correcting a value; and a correction unit that corrects a pixel value of the image data according to the correction coefficient. 2. The area determination unit detects a feature amount indicating a feature of a predetermined range near the image data and outputs the determination result, and the coefficient calculation unit outputs the correction coefficient according to the feature amount. The image processing apparatus according to claim 1, wherein: 3. The apparatus according to claim 2, wherein the area determining means is a low-pass filter for extracting a low-frequency component of the image data, and the coefficient calculating means generates the correction coefficient in accordance with the low-frequency component. The image processing device according to claim 1. 4. The area determining means includes: a quantizing means for quantizing the image data; and a low-pass filter for extracting a low-frequency component from the image data quantized by the quantizing means. The image processing apparatus according to claim 1, wherein the calculating unit generates the correction coefficient according to the low frequency component. 5. The region determining means generates one composite signal based on a plurality of low-pass filters for extracting low-frequency components of the image data, respectively, and a low-frequency component output from the plurality of low-pass filters. The image processing apparatus according to claim 1, further comprising: a signal synthesizing unit configured to generate the correction coefficient based on the synthesized signal. 6. The image processing apparatus according to claim 5, wherein the signal synthesizing unit generates the synthesized signal by performing weighted averaging of low-frequency components output from the plurality of low-pass filters. 7. The signal combining means according to claim 1, wherein said combined signal is generated by weighting and adding low-frequency components output from said plurality of low-pass filters using a weighting coefficient set in advance. 6. The image processing device according to 5. 8. The region determining means has a plurality of low-pass filters for extracting low-frequency components of the image data, respectively, and the coefficient calculating means calculates a low-frequency component based on low-frequency components output from the plurality of low-pass filters. The image processing apparatus according to claim 1, further comprising: a partial coefficient calculation unit configured to generate a correction coefficient; and a coefficient synthesis unit configured to generate the correction coefficient based on the correction coefficient. 9. The image processing apparatus according to claim 8, wherein said coefficient synthesizing unit generates the correction coefficient by performing a weighted average of the correction coefficient. 10. The image processing apparatus according to claim 8, wherein the coefficient synthesizing unit generates the correction coefficient by weighting and adding the correction coefficient using a weighting coefficient set in advance. . 11. The image processing apparatus according to claim 1, wherein the correction unit corrects a pixel value of the image data by multiplying a pixel value of the image data by the correction coefficient. 12. The image processing apparatus according to claim 1, wherein the number of bits of the image data output from said correction means is reduced as compared with the number of bits of the input image data. 13. The image processing apparatus according to claim 1, wherein the image data is data obtained by sampling, at a predetermined frequency, a signal obtained by sequentially superimposing an amplitude-modulated color signal on a luminance signal. 14. An image processing apparatus according to claim 1, wherein said image data is data obtained by sampling a color signal at a predetermined frequency. 15. The image processing apparatus according to claim 1, wherein the image data is data obtained by sampling a luminance signal and a color difference signal at a predetermined frequency. 16. An image processing method for correcting the gradation of image data, comprising: an area determining process of determining an area to which the image data belongs and outputting a determination result; and a pixel of the image data based on the determination result. An image processing method comprising: a coefficient calculation process of outputting a correction coefficient for correcting a value; and a correction process of correcting a pixel value of the image data according to the correction coefficient. 17. The area determination process detects a feature amount indicating a feature of a predetermined range near the image data and outputs the determination result, and the coefficient calculation process outputs the correction coefficient according to the feature amount. 17. The image processing method according to claim 16, wherein: 18. The image processing apparatus according to claim 16, wherein the area determining process extracts a low frequency component of the image data, and the coefficient calculating process generates the correction coefficient according to the low frequency component. The image processing method described in the above. 19. The area determination processing includes: a quantization processing for quantizing the image data; and a processing for extracting a low frequency component from the image data quantized by the quantization processing. The image processing method according to claim 16, wherein the correction coefficient is generated according to the low frequency component. 20. The area determination processing includes: extracting a plurality of low frequency components of the image data in different bands; and generating one composite signal based on the plurality of low frequency components. 17. The image processing method according to claim 16, wherein the coefficient calculation processing is a signal synthesis processing, and the correction coefficient is generated based on the synthesized signal. 21. The image processing method according to claim 20, wherein said signal synthesizing process generates the synthesized signal by weighted averaging the plurality of low frequency components. 22. The image processing apparatus according to claim 20, wherein in the signal combining processing, the combined signal is generated by weighting and adding the plurality of low frequency components using a weighting coefficient set in advance. Method. 23. The area determination processing includes extracting a plurality of low-frequency components of the image data from different bands, and the coefficient calculation processing includes generating partial correction coefficients from the low-frequency components. 17. The image processing method according to claim 16, further comprising: a coefficient synthesis process for generating the correction coefficient based on the correction coefficient. 24. The image processing method according to claim 23, wherein in the coefficient combining processing, the correction coefficient is generated by performing a weighted average of the correction coefficient. 25. The image processing method according to claim 23, wherein in the coefficient synthesizing process, the correction coefficient is generated by weighting and adding the correction coefficient using a weighting coefficient set in advance. . 26. The image processing method according to claim 16, wherein said correction processing corrects a pixel value of said image data by multiplying a pixel value of said image data by said correction coefficient. 27. The image processing method according to claim 16, wherein the number of bits of image data obtained by said correction processing is reduced as compared with the number of input bits. 28. The image processing method according to claim 16, wherein the image data is data obtained by sampling, at a predetermined frequency, a signal in which an amplitude-modulated color signal is sequentially superimposed on a luminance signal. 29. The image processing method according to claim 16, wherein said image data is data obtained by sampling a color signal at a predetermined frequency. 30. The image processing method according to claim 16, wherein said image data is data obtained by sampling a luminance signal and a color difference signal at a predetermined frequency.