JP2000156872A - Image processor and its method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively avoid partial contrast reduction and to correct gradation by applying the image processor and image processing method to image processors such as a television(TV) receiver, a video tape recorder, a TV camera, and a printer. SOLUTION: In the case of correcting a pixel value x (i, j) by generating a correction coefficient g (i, j) in accordance with the judged result r (i, j) of an area including input picture data, the operation is controlled so that the spatial resolution of the correction coefficient g (i, j) is switched in accordance with the pixel value x (i, j) of the picture data. Consequently partial contrast deterioration can be effectively avoided, the gradation can be corrected and a natural contrast can be secured even between adjacent areas.

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, when a correction coefficient is generated according to an area to which input image data belongs and a pixel value is corrected, the operation is controlled so that the resolution of the corresponding correction coefficient is switched according to the pixel value of the image data. As a result, it is possible to correct gradation by effectively avoiding partial deterioration of contrast.

[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. 11 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, in this type of signal processing circuit, the input level 1 is changed to the reference level lk.
When the signal level is further increased, the signal level is suppressed and output. In this case, the gradation is corrected at the expense of the contrast of the portion where the signal level is high.

In the characteristic curve diagram shown in FIG. 11, 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. 12 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. 13, in the histogram equalization process, a frequency distribution H which is a 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
By normalizing (l) by the following equation, a level conversion function T (l) is defined.
According to (l), the signal level of the input image is corrected. Here, Fmax is the cumulative frequency distribution C
(L) is the final value, 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.
For example, for the purpose of suppressing the dynamic range and the like, the program is appropriately executed as needed.

[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, in an image processing apparatus or an image processing method, a region to which image data belongs is determined, a determination result is output, and a determination result is output based on the determination result. A correction coefficient for correcting the pixel value of the image data is output, and the pixel value of the image data is corrected according to the correction coefficient. At this time, the resolution of the correction coefficient is switched according to the pixel value of the image data. .

A region to which the image data belongs is determined, a determination result is output, a correction coefficient for correcting the pixel value of the image data is output based on the determination result, and the pixel value of the image data is corrected according to the correction coefficient. For example, the pixel value can be corrected by the same coefficient in the same region, the magnitude relationship of the pixel values can be maintained in the region, and the magnitude relationship of the pixel values can be reversed between pixels belonging to different regions. It is possible to correct the entire gradation while avoiding a significant deterioration in contrast.

When the gradation is corrected in this manner, the contrast between the regions is determined by the correction means and the slope of the level conversion function, which is the input / output characteristic of the image data in the correction processing, and the spatial resolution of the determination result is reduced. The higher the value, the greater the effect of the level conversion function on the gradation correction result. Therefore, when the pixel value corresponds to a portion having a small slope in the level conversion function, by increasing the resolution in the correction coefficient, even if the level conversion function does not maintain a monotonous increase, the influence of this level conversion function can be reduced. This makes it possible to reduce an unnatural change in contrast between adjacent regions, and natural contrast can be ensured even between adjacent regions.

[0019]

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.

As shown in an enlarged front view of the image pickup surface in FIG. 2, the CCD solid-state image pickup device 2 has a color filter of a complementary color-one pine style arranged on the image pickup surface. That is, the CCD solid-state imaging device 2 includes yellow (Ye) and cyan (Cy).
Are repeated in pixel units to form odd lines, whereas the magenta (Mg) and green (G) color filters are repeated in pixel units to form even lines.

As a result, in the CCD solid-state imaging device 2, as shown in FIG. 3, the color signals subjected to amplitude modulation are sequentially converted into luminance signals by time division from the correlated double sampling circuit associated with this type of imaging device. The superimposed imaging result is output.

To output such an imaging result, C
The CD solid-state imaging device 2 obtains an imaging result in a cycle of 1/60 [second] according to a charge accumulation time set by a user, and outputs the imaging result as an imaging result VN by normal exposure.
Further, in the vertical blanking period of the imaging result VN obtained by the normal exposure, the CCD solid-state imaging device 2 obtains an imaging result with a charge accumulation time shorter than the charge accumulation time by the normal exposure. Is output as the imaging result VS.

As a result, as shown in FIG. 4, in the CCD solid-state imaging device 2, the imaging result VN (FIG. 4 (A)) by the normal exposure in which the output level is saturated when the incident light amount is more than a predetermined amount, 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. 4B) is output as a set.

The memory 4N inputs the imaging result VN by the normal exposure via a correlated double sampling circuit, a defect correction circuit, an analog-to-digital conversion circuit, etc., and temporarily holds the imaging result VN by the normal exposure. Output.

Similarly, the memory 4S inputs the imaging result VS of the short-time exposure via a correlated double sampling circuit, a defect correction circuit, an analog-to-digital conversion circuit, etc. VS 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 obtained 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. 4C) with a much larger dynamic range than in the past.

The gradation correction circuit 8 corrects the pixel value of the imaging result VT to correct and output the gradation of the imaging result VT. In the television camera 1,
A subsequent signal processing circuit (not shown) executes various signal processing required 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 changed so as to correspond to the output device. By uniformly suppressing, the dynamic range of the imaging result is suppressed and output.

That is, in the gradation correction circuit 8, the area judgment filter 9 judges the area to which the input image data belongs, and outputs the judgment result.

That is, the area judgment filter 9 inputs each pixel value x (i, j) of the imaging result VT to the first and second low-pass filters (LPF) 9A and 9B, and limits the band here. Accordingly, the area determination filter 9 determines which of the average luminance levels the input image data belongs to in the low-pass filters 9A and 9B, respectively, and determines the low frequency components r0 (i, j) and r1 as the determination results.
(I, j) is output. Further, at this time, the region determination filter 9 performs these processes simultaneously and in parallel in the low-pass filters 9A and 9B having different pass bandwidths, so that the low-frequency components r0 (i, j) that are the determination results at different resolutions are obtained. ) And r1 (i, j). In this embodiment, as shown in FIG. 5, for the imaging results VT input in the raster scanning order, 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.

That is, the first and second low-pass filters 9A and 9B are two-dimensional low-pass filters, respectively. For the pixel value x (i, j) of the image data sequentially input in the raster scanning order, The low frequency component r (i, j) expressed by the following equation is detected, and this low frequency component r (i, j) is output as the determination result of each area.

[0033]

(Equation 3)

In the equation (3), N and M are constants representing the size of the neighboring area for calculating the average value. As a result, the first and second low-pass filters 9A and 9B remove the fine structure in the image from the image obtained by the imaging result VT to extract a region having a relatively flat pixel value, and determine the determination result based on different resolutions at a low frequency. Components r0 (i, j) and r1
Output as (i, j). Note that the low-pass filter 9A
And 9B aim at such processing, it is desirable that the band is relatively narrow.

Further, the first and second low-pass filters 9
A and 9B are compared with the second low-pass filter 9B.
The constants N and M in equation (3) are selected so that the first low-pass filter 9A forms a low-resolution low-pass filter.

The weighting coefficient generation circuit 9C calculates the low-frequency components r0 (i, j) output from the first and second low-pass filters 9A and 9B by the following equation based on the first low-pass filter 9A. ) And r1 (i,
Generate the weighting factors 1-w and w of j).

[0037]

(Equation 4)

Here, Dmax and Dmin are constants for normalization. In addition, wmax and wmin are the maximum value and the minimum value of the values calculated as the weighting coefficients, and both are given values of 0 or more and 1 or less in advance. The function D (l) is a function determined by a coefficient calculation function G used in the subsequent coefficient calculation circuit 11, and is defined by the following equation.

[0039]

(Equation 5)

As a result, the weighting coefficient generation circuit 9C
When the corresponding pixel value x (i, j) corresponds to a portion where the slope of the level conversion function T (l) described later is small, the value of the weighting coefficient w is increased.

The multiplying circuits 9A and 9B produce low frequency components r0 (i, j) by weighting coefficients 1-w and w, respectively.
And r1 (i, j) are weighted, and then the addition circuit 9
F adds the weighting results obtained by the multiplication circuits 9A and 9B and outputs the result as one region determination result r (i, j).

Thus, in the area determination filter 9, the following weighting addition processing is executed, and for the area corresponding to the portion where the slope of the level conversion function T (l) is large, the low-frequency component band-limited by the high resolution is used. r1
The area determination result r of 1 is increased by increasing the ratio of (i, j).
Conversely, (i, j) is output. In contrast, for a region corresponding to a portion where the slope of the level conversion function T (l) is small, the low frequency component r0 (i, By increasing the ratio of j), the area determination result r of 1 is obtained.
(I, j) is output.

[0043]

(Equation 6)

Thus, in the area determination filter 9, the spatial resolution is switched according to the pixel value x (i, j) of the imaging result VT, that is, the input / output characteristics of the coefficient calculation circuit 11 described later. Level conversion function T (l)
The smaller the inclination of the part, the smaller the determination result r
The determination result r (i, j) is generated such that the spatial resolution of (i, j) is reduced.

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.

[0046]

(Equation 7)

As a result, the coefficient calculation circuit 11 generates and outputs a contrast correction coefficient g (i, j) by the arithmetic processing of 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).

[0048]

(Equation 8)

The multiplying circuit 12 multiplies the pixel value x (i, j) of the imaging result VT by using the contrast correction coefficient g (i, j) generated in this way, thereby obtaining the contrast correction coefficient g ( i, j), the signal level of the imaging result VT is corrected and output.

(1-2) Operation of First Embodiment In the above configuration, in the television camera 1 (FIG. 1), the CDD solid-state image pickup device is formed by the color filters arranged on the image pickup surface (FIG. 2). 2, an image pickup result is output in which the color signal subjected to the amplitude modulation is superimposed on the luminance signal by time division (FIG. 3).

Further, in the television camera 1, an imaging result VN (FIG. 4A) by the normal exposure based on the charge accumulation time set by the user and an imaging result VS (FIG. 4A) of the short exposure based on the short charge accumulation time. B)) are output alternately, and the imaging results VN and VS are stored in the memory 4 respectively.
N and 4S. In television camera 1,
The two imaging results VN and VS are output to the level correction circuit 6,
The image pickup result VT is synthesized by the adder circuit 5 and has a significantly larger dynamic range as compared with the related art.
(FIG. 4C) is generated.

In this imaging result VT, the regions to which the input image data belongs are determined at different resolutions by the low-pass filters 9A and 9B of the region determination filter 9, and the determination results are generated. More specifically, low-pass filters 9A and 9B in which low-frequency components r0 (i, j) and r1 (i, j) indicating an average luminance level which is an average value of pixel values x (i, j) are different bands. , Whereby fine structures in the image are removed, and a region having relatively flat pixel values is extracted.

In the imaging result VT, the two low-frequency components r0 (i, j) and r1 (i, j) are combined by a weighted average circuit including multiplication circuits 9D and 9E and an addition circuit 9F to obtain one low-frequency component. The component r (i, j) is output as a determination result of each area.

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 of the imaging result is corrected in the multiplication circuit 12 by (i, j).

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.
(I, j) pulsates at a frequency equal to or higher than the cutoff frequency of the area determination filter 10 which is a low-pass filter, and the DC level of the pixel value x (i, j) rises rapidly (FIG. 7). (B)), when the change of the low frequency component r (i, j) corresponding to the rapid change of the DC level crosses the inflection point of the coefficient calculation function G (l) (FIG. 7A), According to the conventional level conversion function described above with reference to FIG. A, the contrast is suppressed at a portion where the pixel value is large in the correction result Y (i, j) (FIG. 7C).

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. 7D).

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.

As a result, in the gradation correction circuit 8 according to this embodiment, although the gradation when viewed as a whole does not change significantly, the microscopic pulsation does not affect the imaging result as the input image. The pulsation due to the VT can be increased.

As shown in FIG. 8, similarly, the pixel value x
(I, j) pulsates and the DC level rises sharply, and a large change in the pixel value x (i, j) is biased toward a higher level than the inflection point of the coefficient calculation function G (l). (FIG. 8B), all pixel values x (i, j) may be obtained depending on the conventional level conversion function described above with reference to FIG.
8 suppresses the contrast (FIG. 8).
(C)).

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.
The pulsation due to T can be expanded (FIG. 8).
(D)).

In correcting the gradation of the image pickup result VT in this manner, the gradation correction result y is set within a certain region where the value of the low frequency component r (i, j) is maintained at a substantially constant value.
The contrast at (i, j) is determined by the value of the correction coefficient given by the coefficient calculation function G. On the other hand, the contrast between regions having different values of the low frequency component r (i, j) is determined by the slope of the level conversion function. The size of each region corresponds to the spatial resolution of the correction coefficient g (i, j) and is determined by the pass band width of the low-pass filter that extracts the low frequency component r (i, j).

From these, the low frequency components r (i,
The effect of the level conversion function on the contrast in the gradation correction result y (i, j) increases as the pass band width of the low-pass filter for extracting j) increases, that is, as the resolution of the correction coefficient increases.

As a result, the area to which the predetermined pixel value belongs is
When the level conversion function corresponds to a portion having a small slope, gradation correction is performed based on an area determination result obtained by using a low-pass filter having a narrow passband, that is, the resolution of a correction coefficient corresponding to the determination result is improved. If the gradation correction is performed, even if the monotonic increase property is not maintained in the level conversion function, it is possible to reduce the influence of this level conversion function and reduce the unnatural change in contrast between adjacent areas. It becomes possible.

On the other hand, when the area to which a predetermined pixel value belongs corresponds to a portion having a large slope in the level conversion function, a sufficient contrast is guaranteed in the contrast around the pixel by the slope of the level conversion function. Will be. In this case, in order to improve the gradation correction accuracy of edges and the like in the gradation correction result, a higher-resolution correction coefficient, that is, a region correction result obtained by using a low-pass filter having a wide pass band width, results in a higher-precision correction. A key correction result can be obtained.

As a result, in this embodiment, the level conversion function T is calculated in the weighting coefficient generation circuit 9C based on the low-frequency component r0 (i, j) having a low resolution.
For the region corresponding to the portion where the slope of (l) is large,
Low frequency component r1 (i, i, band-limited by high resolution
j) is increased to output a region determination result r (i, j). Conversely, for a region corresponding to a portion where the slope of the level conversion function T (l) is small, the band is limited by a low resolution. The region determination result r (i, j) is output by increasing the ratio of the calculated low frequency component r0 (i, j).

That is, in the input / output characteristics of the multiplying circuit 12, for a region corresponding to a portion where the slope of the level conversion function T (l) is small, the determination result r (i, j) is reduced so that the spatial resolution is reduced. Generated.

Thus, in the gradation correction circuit 8, a low-resolution correction coefficient is applied to an area where the level conversion function has a small slope, and an area where the level conversion curve has a large slope. , A high-resolution correction coefficient is generated, the gradation is corrected by the correction coefficient generated in this way, and natural contrast can be ensured even between adjacent areas. Can be corrected.

(1-3) Effect of First Embodiment According to the above configuration, a correction coefficient is generated based on the determination result of the area to which the input image data belongs, and the imaging result is corrected according to the correction coefficient. By doing so, it is possible to make the pixel values close to each other as necessary between the pixels belonging to different areas while maintaining the magnitude relation of the pixel values by the same coefficient in the same area, and to reverse the value in extreme cases Can also. As a result, the gradation can be corrected by effectively avoiding partial deterioration of the contrast.

At this time, the determination results having different resolutions are combined, and a low-resolution correction coefficient is assigned to an area composed of a level having a small slope of the level conversion curve. By assigning a high-resolution correction coefficient to the configured region, a natural contrast can be ensured even between adjacent regions, and the gradation can be further naturally corrected.

At this time, by correcting the pixel value of each area with reference to the low-frequency component by the low-pass filter, it is possible to correct the entire gradation while avoiding a partial decrease in contrast with a simple configuration. Can be.

(2) Second Embodiment FIG. 9 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 18 is applied instead of the gradation correction circuit 8 described above with reference to FIG. In the tone correction circuit 18, the same components as those of the above-described tone correction circuit 8 are denoted by the corresponding reference numerals, and duplicate description will be omitted.

In the gradation correction circuit 18, the area judgment filter 19 judges the areas to which the pixel values x (i, j) belong at different resolutions.
1 (i, j) is output.

That is, the area determination filter 19 is a low-pass filter (LPF) 19 having a different pass bandwidth.
A and 19B, each low-pass filter 19
A and 19B are given pixel values x (i, j), and the corresponding low frequency components are determined as determination results r0 (i, j), r1 (i, j).
Output as

Here, the low-pass filters 19A and 19B
Are the low-pass filters 9 described above with reference to FIG.
A and 9B are formed identically.

The coefficient calculation circuit 21 determines the judgment result r0 (i,
j) and r1 (i, j), the corresponding correction coefficient g0 (i,
j) and g1 (i, j) are generated, and the correction coefficients g0 (i, j) and g1 (i, j) are combined to generate one correction coefficient g (i, j).

That is, in the coefficient calculation circuit 21, the coefficient calculation units 21A and 21B determine the determination result r0 (i, i, based on a predetermined coefficient calculation function Gk (k = 0, 1), respectively.
j) and r1 (i, j), the corresponding correction coefficient g0 (i,
j) and g1 (i, j) are generated and output.

The weighting coefficient generation circuit 21C executes the same arithmetic processing as described above for the equation (4) with reference to the pixel value x (i, j) of the imaging result VT. Accordingly, the weighting coefficient generation circuit 21C reduces the value of the weighting coefficient w when the pixel value x (i, j) corresponding to the small gradient of the level conversion function is applicable.

The multiplying circuits 21A and 21B correct the correction coefficient g0 (i, i,
After weighting j) and g1 (i, j), the subsequent adding circuit 21F adds the weighting results obtained by the multiplying circuits 21A and 21B and outputs the result as one correction coefficient g (i, j).

Thus, in the coefficient calculation circuit 21,
A correction coefficient g0 (i, j) according to the pixel value x (i, j),
By manipulating g1 (i, j), the spatial resolution of the correction coefficient g (i, j) is switched.

That is, the pixel value x is added to the portion where the slope of the level conversion function, which is the input / output characteristic of the multiplication circuit 12, is small.
The correction coefficient g (i, j) is set such that the spatial resolution of the correction coefficient g (i, j) is reduced as (i, j) is satisfied.
Generate

More specifically, the coefficient calculating circuit 21 generates a region corresponding to a portion where the slope of the level conversion function T (l) is large from the low frequency component r1 (i, j) band-limited by the high resolution. Correction coefficient g1 (i, j)
Is increased and the correction coefficient g (i, j) of 1 is output. On the contrary, in the area corresponding to the portion where the slope of the level conversion function T (l) is small, the resolution is low. The ratio of the correction coefficient g0 (i, j) generated from the low frequency component r0 (i, j) band-limited by
Output the correction coefficient g (i, j).

According to the configuration shown in FIG. 9, the same effect as in the first embodiment can be obtained even if correction coefficients with different resolutions are generated and then combined to correct the gradation. .

(3) Other Embodiments In each of the above-described embodiments, basically, a case has been described in which a correction coefficient is generated based on the characteristics described above with reference to FIG. 6, 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, a pseudo contour may occur in an image as a processing result because the function is not a monotonically increasing function. However, in the case where the area is determined by the low-pass filter and the processing is performed as in the above-described embodiment, in the vicinity area having a size corresponding to the pass band of the low-pass filter, the pixel value of which the magnitude relation of the pixel value is reversed is reversed. Changes can be prevented. As a result, generation of a false contour can be effectively avoided.

In the above-described embodiment, the case where the coefficient calculation function G is generated by the arithmetic processing of the equation (7) using the level conversion function T has been described. However, the present invention is not limited to this. The coefficient calculation function G may be arbitrarily set without using the function T.

In the above-described embodiment, the case has been described in which the gradation is corrected by the gradation correction circuit and then the dynamic range is suppressed by the subsequent signal processing circuit. However, the present invention is not limited to this, and the level conversion is not limited to this. 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. Where j
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.

[0090]

(Equation 9)

Further, in the above-described embodiment, a case has been described in which the correction coefficients are generated by adaptively processing the outputs of the two low-pass filters. However, the present invention is not limited to this. Is adaptively processed to generate a correction coefficient, and the same effect as in the above-described embodiment can be obtained.

In the above-described first embodiment,
Although the case of synthesizing the outputs of two low-pass filters has been described, the present invention is not limited to this, and the passband of one low-pass filter is adaptively changed according to the input image data, so that the correction coefficient can be adjusted. The resolution of the corresponding determination result may be switched.

Further, in the above-described embodiment, the case has been described in which the imaging result in which the amplitude-modulated color signal is sequentially superimposed on the luminance signal by time division is directly processed.
The present invention is not limited to this. After generating a correction coefficient by separating luminance data from such an imaging result, when correcting the gradation of the imaging result with this correction coefficient, and further when processing a color signal, The present invention can be widely applied to a case where a video signal is processed by a luminance signal and a color difference signal, and a case where a composite video signal obtained by superimposing a chroma signal on a luminance signal is processed.

In the composite video signal, a correction coefficient is generated based on the luminance signal generated by the YC separation,
By correcting the gradation of the luminance signal and the chroma signal, the luminance signal and the color difference signal by using the correction coefficient, the gradation of this kind of video signal can be corrected, and the video signal based on the luminance signal and the color difference signal is processed. In this case, similarly, a correction coefficient is calculated based on the luminance signal, and the gradation of the video signal of this type can be corrected by correcting the gradation of the luminance signal and the color difference signal using the correction coefficient.

In the case of further processing a color signal, a luminance signal is generated by the following arithmetic operation, a correction coefficient is calculated based on the luminance signal, and the gradation of each color signal is corrected using the correction coefficient. Thereby, the gradation of this kind of video signal can be corrected.

[0096]

(Equation 10)

Further, in the above embodiment, the case where the area to which the input image data belongs is determined by the low-pass filter using the average luminance level as the feature amount of the image data, but the present invention is not limited to this. For example, when the similarity between an arbitrarily selected pixel and a neighboring pixel surrounding the pixel is grasped as a feature amount in the image to be processed, and the region is sequentially enlarged from this pixel to determine the region to be processed. In addition, the same effect as that of the above-described embodiment can be obtained by determining the area of the image to be processed by various processing methods by various feature amounts.

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.

[0099]

As described above, according to the present invention, when the correction coefficient is generated based on the determination result of the area to which the input image data belongs and the pixel value is corrected, the correction is performed according to the pixel value of the image data. By controlling the operation so that the spatial resolution of the correction coefficient to be changed is changed, the gradation can be corrected while effectively avoiding the partial deterioration of the contrast. Contrast can be ensured.

[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 plan view showing a color filter of a CCD solid-state imaging device of the television camera of FIG.

FIG. 3 is a signal waveform diagram showing an image pickup result by the color filter of FIG. 2;

FIG. 4 is a characteristic curve diagram for describing processing of an imaging result in the television camera of FIG. 1;

FIG. 5 is a schematic diagram illustrating an array of pixels in the television camera of FIG. 1;

FIG. 6 is a characteristic curve diagram for explaining a contrast correction coefficient g (i, j).

FIG. 7 is a signal waveform chart for describing processing of a gradation correction circuit in the television camera of FIG. 1;

FIG. 8 is a signal waveform diagram for describing processing of a gradation correction circuit at an input level different from that in FIG. 7;

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

FIG. 10 is a characteristic curve diagram for explaining a level conversion function applied to a gradation correction circuit according to another embodiment.

FIG. 11 is a characteristic curve diagram for describing a level conversion function applied to a conventional gradation correction suppression process.

12 is a characteristic curve diagram for explaining a level conversion function applied to a gradation correction process according to another example different from FIG.

FIG. 13 is a characteristic curve diagram for explaining a histogram equalization process.

[Explanation of symbols]

1 ... television camera, 8, 18 ... gradation correction circuit, 9, 19 ... area determination filter, 9A, 9B, 19
A, 19B ... low-pass filter, 9C, 21C ... weighting coefficient generation circuit, 9D, 9E, 12, 21D, 21
E: Multiplication circuit, 9F, 21F: Addition circuit, 11:
Coefficient calculation circuit

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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 Sony Corporation F-term (reference) 5C022 AB02 AC42 5C026 CA02 5C065 AA01 BB08 BB23 BB48 DD02 EE07 EE08 GG02 GG12 GG17 GG21 GG23 GG27 5C077 LL19 MP08 NN02 NP02 PP01 PP15 PP20 PP23 PP27 PP42 PP51 PP68 PQ08 PQ18 TT02 TT06 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. A coefficient calculating unit that outputs a correction coefficient for correcting a value; and a correcting unit that corrects a pixel value of the image data according to the correction coefficient. The area determining unit or the coefficient calculating unit includes a pixel of the image data. The image processing apparatus according to claim 1, wherein the determination result or the correction coefficient is generated such that a resolution of the correction coefficient switches according to a value. 2. The image processing apparatus according to claim 1, wherein the area determining unit or the coefficient calculating unit is configured to:
The method according to claim 1, wherein the determination result or the correction coefficient is generated such that a resolution of the correction coefficient is reduced.
An image processing apparatus according to claim 1. 3. The area determination means detects a characteristic amount indicating a characteristic of a predetermined range near the image data and outputs the determination result, and the coefficient calculation means outputs the correction coefficient according to the characteristic amount. The image processing apparatus according to claim 1, wherein: 4. The apparatus according to claim 1, wherein said area determination means switches the resolution of said correction coefficient by changing a resolution of said determination result according to a pixel value of said image data. Image processing device. 5. The image processing apparatus according to claim 1, wherein said coefficient calculating means switches the resolution of said correction coefficient by correcting said correction coefficient according to a pixel value of said image data. The image processing apparatus according to any one of the preceding claims. 6. The image processing apparatus according to claim 1, wherein the area determination unit is a low-pass filter that extracts a low frequency component of the image data and outputs the determination result. 7. A plurality of low-pass filters having different pass bandwidths for extracting low-frequency components of the image data, respectively, and a low-pass filter output from the plurality of low-pass filters according to the image data. The image processing apparatus according to claim 1, further comprising a signal synthesizing unit that synthesizes a frequency component to generate the determination result. 8. The image processing apparatus according to claim 7, wherein said signal synthesizing unit generates the determination result by performing weighted averaging of low-frequency components output from the plurality of low-pass filters. 9. The area determination means has a plurality of low-pass filters that have different passbands and extract low-frequency components of the image data, respectively, and output the determination result. A partial coefficient calculation unit configured to generate a correction coefficient from each of the low frequency components output from the plurality of low-pass filters; and a coefficient synthesis unit configured to generate the correction coefficient based on the correction coefficient. The image processing apparatus according to claim 1, wherein: 10. The image processing apparatus according to claim 9, wherein said coefficient synthesizing unit generates the correction coefficient by synthesizing the correction coefficient in accordance with the image data. 11. The image processing apparatus according to claim 9, wherein said coefficient synthesizing means generates said correction coefficient by weighted averaging said plurality of correction coefficients according to said image data. . 12. The image processing apparatus according to claim 1, wherein said correction means corrects a pixel value of said image data by multiplying a pixel value of said image data by said correction coefficient. 13. The image processing apparatus according to claim 1, wherein the number of bits of the image data output from the correction means is reduced as compared with the number of bits of the input image data. 14. The image according to claim 1, 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 by time division. Processing equipment. 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, wherein: an area determination process for determining an area to which the image data belongs and outputting a determination result; and determining a pixel value of the image data according to the determination result. A coefficient calculation process of outputting a correction coefficient to be corrected; and a correction process of correcting a pixel value of the image data according to the correction coefficient. In the area determination process or the coefficient calculation process, the pixel value of the image data An image processing method, wherein the determination result or the correction coefficient is generated such that the resolution of the correction coefficient switches in response. 17. The image processing apparatus according to claim 17, wherein in the input / output characteristics of the image data in the correction processing, a change in an output value with respect to a change in an input value is smaller.
The method according to claim 1, wherein the determination result or the correction coefficient is generated such that a resolution of the correction coefficient is reduced.
7. The image processing method according to 6. 18. The area determining process detects a feature amount indicating a feature of a predetermined range in the vicinity of the image data and outputs the determination result. The coefficient calculating process outputs the correction coefficient according to the feature amount. 17. The image processing method according to claim 16, wherein: 19. The resolution of the correction coefficient according to claim 16, wherein the area determination processing switches resolution of the correction coefficient by changing resolution of the determination result according to a pixel value of the image data. Image processing method. 20. The method according to claim 16, wherein said coefficient calculation process switches the resolution of said correction coefficient by correcting said correction coefficient in accordance with a pixel value of said image data. The image processing method described in the above. 21. The image processing method according to claim 16, wherein in the area determination processing, a low frequency component of the image data is extracted and the determination result is output. 22. The area determination processing includes: signal extraction processing for extracting low-frequency components of the image data with different passbands; and combining the plurality of low-frequency components according to the image data. 17. The image processing method according to claim 16, comprising a signal synthesis process for generating a determination result. 23. The image processing method according to claim 22, wherein in the signal synthesis processing, the determination result is generated by performing a weighted average of the plurality of low frequency components. 24. The area determination processing includes extracting low-frequency components of the image data with different pass bandwidths and outputting the determination result, and the coefficient calculation processing includes: 17. The image processing method according to claim 16, comprising: a partial coefficient calculation process for generating a correction coefficient; and a coefficient synthesis process for generating the correction coefficient based on the correction coefficient. 25. The image processing method according to claim 24, wherein in the coefficient synthesizing process, the correction coefficient is generated by synthesizing the correction coefficient according to the image data. 26. The image processing method according to claim 24, wherein in the coefficient synthesizing process, the correction coefficient is generated by performing a weighted average of the plurality of correction coefficients according to the image data. . 27. 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. 28. 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 bits of input image data. 29. The image according to claim 16, wherein said image data is data obtained by sampling a signal obtained by sequentially superimposing an amplitude-modulated color signal on a luminance signal by time division at a predetermined frequency. Processing method. 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.