JP2002027285A - Gradation correcting device gradation correcting method, medium and information aggregate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optimum gradation correction characteristic without suppressing the gradation correction characteristic even if a dynamic range is low. SOLUTION: A microcomputer 4 as a gradation correction characteristic calculating means changes the gradation correction characteristic and outputs it from a gradation correction means 5 by the dynamic range of an input signal obtained from a dynamic range detecting means such as a peak detecting circuit 2, for example, and by information of a histogram detecting means 3 showing the appearing frequency of the signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gradation correction device, a gradation correction method, a medium, and an information aggregate used for a video camera or the like.

[0002]

2. Description of the Related Art As a conventional gradation correcting apparatus, Japanese Patent Application No. 9-90, filed on Jan. 19, 1993.
The one described in JP-A-012844 is known.

FIG. 12 shows a configuration diagram of a conventional gradation correction device. In FIG. 12, 1 is an input terminal, 3 is a histogram detecting means, 4 is a gradation correction characteristic calculating means, 5 is a gradation correcting means, and 6 is an output terminal.

In a conventional tone correction device, an input signal input from an input terminal 1 is calculated by a histogram detection means 3 to calculate a histogram of luminance values corresponding to one screen of the input signal. Note that the histogram detection means 3 divides the input signal into a plurality of equally-spaced levels, and detects a luminance value distribution (histogram) for each level.

The gradation correction characteristic calculating means 4 calculates a gradation correction characteristic such that the inclination changes according to the detected histogram. The gradation correction characteristics are set so that the slope is large when the distribution of the histogram is large and the gradient is small when the distribution is small, but the distribution is concentrated on some signal levels and the gradient of that level is too large. In this case, the noise component included in the signal is also enlarged, resulting in an unnatural image. When the histogram is large, the slope is set to a constant value.

FIG. 13 shows a histogram distribution and a gradation correction characteristic of a conventional gradation correction device. In FIG. 13, (a)
Is a histogram, the horizontal axis is the division level of the input signal, and the vertical axis is the frequency distribution (histogram) corresponding to each signal level of the input signal. (B) is a gradation correction characteristic, the horizontal axis is the input signal level, and the vertical axis is the output signal level.

In FIG. 13 (b), the accumulation of the histogram distribution of FIG. 13 (a) becomes the gradation correction characteristic, and the distribution corresponding to each division level corresponds to the gain of that division level. For this reason, the gain of the tone correction characteristic corresponding to the input signal level corresponding to the frequent division level in FIG. 13A is set to be large, and the contrast of the frequent division level is emphasized. You. Conversely, the gain of the gradation correction characteristic corresponding to the input signal level corresponding to the infrequently divided level in FIG. 13A is set to be small and the slope is gentle.

Here, the gains corresponding to the third and twelfth division levels are suppressed to the levels indicated by the broken lines in FIG.

The tone correction means 5 performs tone correction based on the tone correction characteristics calculated by the tone correction characteristic calculation means 4 and outputs the result from an output terminal 6.

As described above, the gradation correction process is performed to output a limited dynamic range of an input signal having a large dynamic range by suppressing a part of the gradation characteristics.

[0011]

However, in the above configuration, constant control is performed regardless of the dynamic range represented by the difference between the minimum value and the maximum value of the input signal. However, there is a problem (first problem) that unnecessary gain is suppressed and an unnatural image is formed.

Further, if gradation correction is performed when the dynamic range is smaller than a predetermined value, the gradation may be suppressed to a necessary portion (second problem).
There is.

There is also a problem (third problem) that a peak detection circuit for detecting a peak level of an input signal is required as a dynamic range detecting means.

In the camera signal processing, the low-luminance portion is emphasized by gamma correction or the like, which greatly affects the contrast and resolution of the entire screen. However, since the gain of the low-luminance portion is suppressed, the screen is reduced. There is a problem (fourth problem) that the overall resolution is deteriorated.

The present invention has been made in consideration of the above first problem, and a tone correction apparatus, a tone correction method, and a medium which do not produce an unnatural image even when tone processing is performed on various signals having different dynamic ranges. And an information aggregate.

Further, in consideration of the above second problem, the present invention provides a process which does not suppress the gradation to a necessary portion even if the gradation is corrected when the dynamic range is smaller than a predetermined value. It is an object to provide a tone correction device, a tone correction method, a medium, and an information aggregate.

Further, in consideration of the third problem, the present invention provides a gradation correction device, a gradation correction method, and a medium which do not require a peak detection circuit for detecting a peak level of an input signal as dynamic range detection means. And an information aggregate.

Another object of the present invention is to provide a gradation correction device, a gradation correction method, a medium, and an information aggregate in which the resolution of the entire screen is not degraded in consideration of the fourth problem. Things.

[0019]

In order to solve the above-mentioned problems, a first invention (corresponding to claim 1) comprises a dynamic range detecting means for detecting information on a dynamic range of an input signal; Histogram detecting means for dividing the signal into a plurality of division levels in the signal level direction and detecting histogram data which is the frequency of appearance of the signal for each of the division levels; and information on the detected histogram data and the detected dynamic range. On the basis of the,
A tone correction characteristic calculating unit that calculates a tone correction characteristic of the signal for each of the division levels; and a tone correction unit that performs tone correction on the input signal based on the calculated tone correction characteristic. It is a gradation correction device characterized by comprising:

Further, the second invention (corresponding to claim 2)
The tone correction characteristic calculation means calculates a slope, which is a ratio of a change amount of an output signal to a change amount of a level of an input signal in the tone correction characteristic, to the appearance of the signal of the histogram data for each of the division levels. Calculating the gradation correction characteristic by associating the obtained inclination with a frequency, limiting the obtained inclination to a predetermined range, and changing the obtained restriction range of the inclination according to the information of the dynamic range. 1 is a gradation correction apparatus according to a first aspect of the present invention.

The third invention (corresponding to claim 3)
The tone correction device according to the first or second aspect of the present invention, wherein the tone correction characteristic calculating means does not change the tone correction characteristic when the dynamic range is smaller than a predetermined value. .

A fourth aspect of the present invention (corresponding to claim 4)
Wherein the dynamic range detecting means obtains the information of the dynamic range based on the highest division level in which the input signal is distributed among the histogram data. It is a gradation correction device of the description.

The fifth invention (corresponding to claim 5)
Divides an input signal into a plurality of division levels in a signal level direction, detects histogram data which is a frequency of appearance of a signal for each of the division levels, and performs the division based on the detected histogram data. A tone correction characteristic calculating unit that calculates a tone correction characteristic of a signal for each level; and a tone correction unit that performs tone correction on the input signal based on the calculated tone correction characteristic, The gradation correction characteristic calculating means may calculate a gradient, which is a ratio of a change amount of an output signal to a change amount of a level of an input signal in the gradation correction characteristics, with an appearance frequency of the signal of the histogram data for each of the division levels. The slope of the gradation correction characteristic for each of the division levels is limited to a predetermined range, and the control range of the gain of the division level of the low luminance portion is made smaller. A gradation correction apparatus characterized by Kusuru.

The sixth invention (corresponding to claim 6)
Fixing a gain of a division level of a lowest luminance part among the division levels of the low luminance part.
Is a gradation correction device according to the present invention.

Further, a seventh aspect of the present invention (corresponding to claim 7)
Calculates a tone correction characteristic based on information of a dynamic range of an input signal and histogram data which is an appearance frequency of a signal for each division level obtained by dividing the input signal into a plurality of levels in a signal level direction, A tone correction method, wherein tone correction is performed on the input signal based on the calculated tone correction characteristics.

The eighth invention (corresponding to claim 8)
Is a medium that carries a program and / or data for causing a computer to execute all or a part of the functions of all or a part of the tone correction device according to any one of the first to sixth aspects of the present invention. And a medium characterized by being processable by a computer.

The ninth invention (corresponding to claim 9)
Is a program and / or data for causing a computer to execute all or a part of functions of all or a part of the tone correction device according to any one of the first to sixth aspects of the present invention. Is an information aggregate.

[0028]

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

(Embodiment 1) Hereinafter, a gradation correcting apparatus according to Embodiment 1 of the present invention will be described with reference to the drawings.

In the first embodiment, a natural image can be obtained even with a signal having a small dynamic range by changing the gradation correction characteristic in the gradation correction characteristic calculating means based on the information on the dynamic range of the input signal. The gradation correction device will be described.

FIG. 1 is a configuration diagram showing the configuration of the tone correction device according to the first embodiment of the present invention.

In FIG. 1, 1 is an input terminal, 2 is a peak detecting circuit as dynamic range detecting means, 3 is a histogram detecting means, 4 is a microcomputer as gradation correcting characteristic calculating means, 5 is a gradation correcting means, 7 is a division level setting register, 8 is a comparator, 9 is an output terminal, 1
0 is a signal level determination circuit, 11 is a multiplexer, 12
Is a histogram register, 13 is a selector, and 14 is an adder.

The greater the number of division levels for gradation correction, the finer the gradation correction, but the larger the circuit scale. In the present embodiment, the number of division levels is 16
And

The tone correcting apparatus of the present embodiment is used by being incorporated in, for example, a video camera or a digital camera. Both the input signal Sin and the output signal Sout are digital signals, and the input signal Si
It is assumed that the number of gradations that can be represented by n is greater than the number of gradations that can be represented by the output signal Sout. For example, the input signal Sin is
Digital data expressing gradation with 18 bits,
It is assumed that the output signal Sout is digital data that expresses a gradation by 8 bits.

Next, the operation of the embodiment will be described.

The input signal Sin input from the input terminal 1
Is input to a peak detecting circuit 2 as a dynamic range detecting means, and a peak level P which is a signal level having the highest luminance level among signals of one screen is detected and input to the microcomputer 4. Since the dynamic range is a distribution range of the signal level, the dynamic range is wide when the peak level is high, and the dynamic range is narrow when the peak level is low.

The input signal Sin input from the input terminal 1
Is input to the histogram detection means 3 simultaneously with the peak detection circuit 2 as the dynamic range detection means. The histogram detecting means 3 includes division level setting registers 7a to 7
16 division level data S (n) set to p, n = 0,
1,2,3, ..., 15, the comparators 8a to 8p input signals Si
By comparing n with the 16 division level data, the signal level determination circuit 10 determines which of the 16 division levels the input signal is in, and transmits it to the multiplexer 11 and the selector 13 as a control signal.

Here, the division level set in the register 7 is set so as to divide the distribution range of the input signal at equal intervals. However, the low luminance part may be finely divided and the high luminance part may be exposed.

In the histogram detecting means 3, the multiplexer 11 and the selector 13 are controlled by a control signal, and the multiplexer 11 and the selector 13 are connected to the 16 registers 12a.
The register corresponding to the input signal level is selected from .about.12p. The adder 14 adds 1 to the output signal of the selected register 12 and stores the same in the same register 12 again. By performing this operation over one field period, histogram data H (0) to H (15), which are distributions of luminance values corresponding to 16 levels, can be obtained.

The size of the histogram data H (n) depends on the number of samples of the input signal. As the number of samples increases, a more stable value can be obtained, but the processing in the microcomputer requires a load. The number of samples for one screen is sufficient if there are 512 samples, and the histogram detecting means 3 adjusts the sample interval so that 512 samples are detected for one screen with respect to the input signal.

The histogram data H (0) to H (15) corresponding to the 16 levels obtained as described above.
Is transferred to the microcomputer 4 within the blanking period of the television signal.

In the microcomputer 4, using the histogram data H (0) to H (15), the initial clip (S1), the first normalization (S2), the first MAX, MI
N clips (S3), second normalization (S4), second M
The gradation correction characteristic is calculated according to a five-stage algorithm such as AX and MIN clip (S5).

FIG. 2 shows a flowchart of the algorithm for calculating the gradation correction characteristic.

First, the microcomputer 4 performs an initial clip process (S1).

In the initial clipping process (S1), of the input histogram data H (0) to H (15), those having a size equal to or larger than the predetermined clip level CL are set to the value CL.
Clip to Depending on the image, the histogram data may be concentrated on some division levels. However, when the gradation is concentrated on some of the division levels, the inclination of the division level is too large, and the gradation characteristics such as the deterioration of S / N become unnatural. Here, the reason why the histogram data is clipped is to avoid concentration of gradations at some division levels. The clip level is desirably about 1/8 of the number of samples of all histogram data, and is 64 for 512 samples.

FIG. 3A shows an example of histogram data. In FIG. 3A, the horizontal axis represents the division level from 0 to 15 levels, and the vertical axis represents the frequency for each division level. FIG.
In (a), the frequency is concentrated on the division levels of the third and twelfth steps, and the clip processing is performed by the CL.

The microcomputer 4 calculates the tone correction characteristic SH (n) after the initial clip processing. The gradation correction characteristics are represented by histogram data H (0) to H (15).
From SH (0) to SH (15). The cumulative integral SH (n) is expressed by the following equation 1 using H (n).

[0048]

## EQU1 ## SH (n) = ΣH (k) k = 0, 1, 2,..., N FIG. In FIG. 3B, the horizontal axis represents the division level, and the vertical axis represents the cumulative integral SH representing the gradation correction characteristic.
The gradation correction characteristic when clip processing is not performed is indicated by a broken line a, and the gradation correction characteristic when clip processing is performed is indicated by a solid line b. In the two curves in FIG.
The inclination at the step is suppressed in b after clip processing. Since the difference between the gradation correction characteristics for each division level corresponds to the histogram data H (n), the gradient of each division level of the gradation correction characteristic SH is represented by the histogram data H (n) for each division level. become.

Comparing a and b in FIG. 3B, the maximum value represented by the gradation correction characteristic SH (15) at the fifteenth division level changes due to the initial clipping process (S1). .

Next, in the microcomputer 4, for the gradation correction characteristic whose maximum value has changed, the maximum value is a constant value SH.
The first normalization process (S2) is performed so as to be max.

The histogram data Hnorm after the normalization processing
1 (n) is expressed by the following Expression 2 by multiplying the histogram data after the initial clip processing by SHmax / SH (15).

[0052]

Hnorm1 (n) = H (n) × SHmax / SH
(15) n = 0, 1, 2,..., 15 Here, SHmax is set so as to correspond to the maximum value of the output signal of the gradation correction means 5. Here, SHmax = 5
Set to 12.

FIG. 3C shows the gradation correction characteristics after the first normalization processing. In FIG. 3C, a dashed line b shows the characteristics before the normalization process, and a solid line c shows the characteristics after the normalization process. In FIG. 3C, the gradation correction characteristic after the normalization processing of c reaches the maximum value SHmax of the output signal of the gradation correction means 5 at the 15th stage,
This means that the gradation reproduction range is effectively used.

Next, the microcomputer 4 limits the gradient of each divided level to the histogram data Hnorm1 (n) after the first normalization processing.
X, MIN clip processing (S3) is performed.

First MAX and MIN clip processing (3)
Let MAX (n) be the maximum slope of each division level and MIN (n) the minimum slope of each division level. If the histogram data Hnorm (n) of each division level is larger than the maximum value MAX (n), MAX (n) contains histogram data Hnorm
If (n) is smaller than the minimum value MIN (n), clip processing is performed so as to be MIN (n).

If the gradient of the gradation correction characteristic is too large, the S / N ratio of the image is degraded, and if the gradient is too small, the gradation is lost. Since the maximum value MAX suppresses S / N deterioration, the minimum value MIN is determined so as to suppress gradation loss. Here, the values of the maximum value MAX (n) and the minimum value MIN (n) are assumed to be 64 and 8 for all the division levels. FIG. 3D shows the first MAX,
5 shows the gradation correction characteristics after the MIN clip processing. FIG.
In (d), the dashed line c is the gradation correction characteristic before the MAX and MIN clip processing, and the solid line d is the gradation correction characteristic after the MAX and MIN clip processing.

The maximum value of the gradation correction characteristic also changes by performing the first MAX and MIN clip processing (S3).

Next, in the microcomputer 4, the maximum value is again changed to the constant value S for the gradation correction characteristic whose maximum value has changed.
The second normalization process (S4) is performed so as to be Hmax. The operation of the second normalization process is the same as the operation of the first normalization process. Similar to the first normalization process, the gradation correction characteristics after the normalization process are the same as those in the fifteenth division level. The maximum value SHmax of the output signal of the correction means 5 is reached, and the gradation reproduction range can be used effectively.

Next, the microcomputer 4 limits the slope of each divided level to the histogram data Hnorm2 (n) after the second normalization processing.
X, MIN clip processing (5) is performed. The second MAX,
In the MIN clip processing, unlike the first MAX and MIN clip processing, the values of the clip values MAX (n) and MIN (n) are changed according to the peak level P detected by the peak detection circuit 2.

That is, when the peak level P is small, MIN (n) is set large, and when P is large, MIN (n) is set small. FIG. 4 shows the relationship between the peak level and MIN (n). Here, the maximum value of MIN (n) is 64,
The minimum value is 8.

Although MAX (n) may be changed, it is not always necessary to change it.

Further, instead of setting the maximum value of MIN (n) to 64 and the minimum value to 8, MIN (n)
An initial value of (n) is determined in advance, and when the peak level P is small, MIN (n) for each division level is set to be larger than a preset initial value, and when P is large, MIN (n) is set. n) may be set smaller than a preset initial value.

FIG. 5A shows histogram data when the peak level is low. When the peak level is low, the histogram data is also distributed at a low division level.
FIG. 5B shows the gradation correction characteristic when the second MAX and MIN clip processing is not performed by a broken line a and the second MAX and MI.
The solid line b shows the gradation correction characteristic when the N clip processing is performed.

When the peak level is low, the dynamic range is low, so that it is not necessary to suppress the gradient of the gradation correction. MIN in the second MAX and MIN clip processing
By increasing the clip value, even when the dynamic range is low, it is possible to obtain an optimum gradation correction characteristic without suppressing the gradation correction characteristic.

The gradation correction means 5 performs gradation correction processing on the input signal Sin input from the input terminal 1 based on the gradation correction characteristics calculated by the microcomputer 4 and outputs an output signal Sout from the output terminal 9.

In the gradation correction processing, a gain A (n) and an offset B (n) are given to the input signal Sin for each of the same division levels as the histogram detection means 3, and a polygonal line based on the following equation 3 It is output as an output signal Sout from the approximation.

[0067]

Sout = A (n) × (Sin−S (n)) + B (n) where A (n) = (SH (n + 1) −SH (n)) / (S (n +) 1) −
S (n)) and B (n) = SH (n).

FIG. 6 shows the relationship between SH (n) and S (n).

As described above, the effect of the present embodiment is that the gradation correction characteristic is changed by the gradation correction characteristic calculation means based on the information on the dynamic range of the input signal obtained from the dynamic range detection means. Even if it is low, without suppressing the tone correction characteristics,
That is, optimum tone correction characteristics can be obtained.

In this embodiment, the microcomputer 4 is used as the gradation correction characteristic calculation means for calculating the gradation correction characteristic SH (n) from the histogram data H (n) detected by the histogram detection means 3. The same effect can be obtained even if part or all of the operation of the microcomputer 4 is realized by hardware or other means.

In this embodiment, the division levels for histogram detection and gradation correction are set at equal intervals.
The setting may be such that the low-brightness part is fine and the high-brightness part is coarse. Of course, the control of the part where the width of the division level is made fine enables fine control. In a video camera or the like that emphasizes the gradation characteristics of a signal in a low luminance portion by gamma correction, it is effective to make the division of the low luminance portion fine.

In the present embodiment, the signal division level is set to 16 divisions, but may be larger or smaller. As the number of divisions increases, finer control becomes possible, but the amount of processing required for calculating the gradation correction characteristics increases, and a load is imposed on the microcomputer and hardware.

Further, in this embodiment, the gradation correction characteristic calculating means limits the gain control range for each division level and changes the gain control range based on the dynamic range information, so that the gradation correction characteristic is calculated. Although it has been changed, a configuration may be used in which a plurality of gradation correction characteristics corresponding to the dynamic range are prepared, and the gradation correction characteristics are switched based on the information of the dynamic range. However,
In that case, fine control for each division level as in the present embodiment is impossible.

An advantage of the present invention is that an optimum gradation correction characteristic can be obtained without suppressing the gradation correction characteristic even when the dynamic range is low.

(Embodiment 2) In the first embodiment, the second M
In the AX and MIN clip processing, the peak level and M
When the relationship of IN (n) is simply the peak level P is small, MIN (n) is large, and when P is large, MIN (n) is set small.
When N (n) is small, the gradation of the low-luminance part is suppressed, which may result in an unnatural image.

In the second embodiment, the configuration of the gradation correction device and the algorithm up to the second normalization process in the microcomputer 4 are the same as those in the first embodiment, and therefore are omitted, and the second MAX and MIN clip processes (5 ) Will be described.

The second MAX of the microcomputer 4,
In the MIN clip processing, the way of changing the clip level MIN (n) corresponding to the peak level differs. That is, when the peak level P is small, MIN (n) is set large, and when P is large, MIN (n) is set small. However, when the maximum value of the variable range of the peak level is Pmax, When the level is equal to or less than 1/2 of Pmax, MIN (n) is set to the same value as MAX (n). When the peak level is Pmax, MIN (n) is set to 1/8 of MAX (n).
Set to. The peak level is Pmax and 1 / Pmax of Pmax.
In the case of a range between two, the set value is interpolated according to the peak level. FIG. 7 shows the relationship between the peak level and MIN (n). Here, the maximum value of MIN (n) is 64, and the minimum value is 8.

FIG. 8A shows histogram data when the peak level is low. When the peak level is low, the histogram data is also distributed at a low division level.
FIG. 8 (b) shows the gradation correction characteristics when the second MAX and MIN clip processing is not performed by a broken line a for the second MAX and MIN.
The solid line b shows the gradation correction characteristic when the clip processing is performed.

When the peak level is low, it is not necessary to suppress the gradient of the gradation correction because the dynamic range is low. MIN in the second MAX and MIN clip processing
By increasing the clip value, even when the dynamic range is low, it is possible to obtain an optimum gradation correction characteristic without suppressing the gradation correction characteristic.

The operation after the gradation correcting means 5 is the same as that of the first embodiment.
Therefore, the description is omitted here.

As described above, the effect of the present embodiment is that the gradation correction characteristic calculating means uses the information on the dynamic range detected by the dynamic range detecting means when the dynamic range of the input signal is smaller than a predetermined value. By fixing the gradation correction characteristics, the optimum gradation correction characteristics can be obtained without suppressing the gradation correction characteristics even when the dynamic range is low.

In the second embodiment, when the dynamic range for fixing the MIN clip value is Pmax, the maximum value of the variable range of the peak level is Pmax, but the peak level is １ ／ of Pmax. It is not limited to two.

(Embodiment 3) Although the peak detection circuit 2 is used as the dynamic range detection means in the first and second embodiments, the dynamic range can be detected by means other than the peak detection circuit in order to reduce the circuit scale. It is desirable.

In the third embodiment, a description will be given of a gradation correction apparatus which can reduce the number of peak detection circuits by using histogram data detected by the histogram detection means as the dynamic range detection means.

Hereinafter, a gradation correcting apparatus according to a third embodiment of the present invention will be described with reference to the drawings.

FIG. 9 shows a configuration of a gradation correction apparatus according to the third embodiment. In FIG. 9, 1 is an input terminal, 3 is a histogram detection means, 4 is a microcomputer as a gradation correction characteristic calculation means, and 5 is a gradation correction means. The configuration of FIG. 9 is obtained by removing the peak detection circuit 2 from the configuration diagram of the first embodiment shown in FIG.

In the third embodiment, the operation of the histogram detecting means 3 is the same as that of the first embodiment, and will not be described here.

In the third embodiment, the microcomputer 4
, A dynamic range is detected using the histogram data obtained by the histogram detecting means 3.
The detection of the dynamic range is performed by the following algorithm. FIG. 10 shows a dynamic range detection algorithm according to the third embodiment.

Note that also in the third embodiment, the number of division levels in the histogram detection means 3 is 1 from 0 to 15.
There are six stages.

The dynamic range is represented by a peak level which is the maximum value of the input signal. Histogram detection means 3
The histogram data H (n) detected in (1) represents the frequency of the signal for each division level, and the highest division level in which the signal is distributed represents the peak level.

The highest division level at which the signal is distributed is the highest division level at which the histogram data is not 0. However, simply detecting whether the histogram data is 0 or not simply means that the peak of the signal level such as a tree leakage day is detected. When the level changes drastically, the detection data becomes unstable.

Here, in order to obtain the stability of the peak level, the peak level is not changed with respect to a change of the histogram data which is smaller than a certain level.

First, regarding the histogram data H (n) obtained by the histogram detecting means 3, the first threshold value th1 is set in order from the higher division level (here, 15).
(S7, S8), and first, a division level at which H (n) exceeds the first threshold th1 is set as a first peak level p1 (S9).

Next, the first peak level p1 is compared with the previously detected peak level p0 (S10).
If it is larger, the first peak level p1 is set as the current detected peak level p2 (S11).

If the first peak level p1 is smaller than the previously detected peak level p0, H (n) is changed to p
The second smaller than the first threshold th1 in ascending order from 0
, The first division level at which the histogram data H (n) becomes larger than the second threshold th2 is set as the current detection peak level p2 (S13, S14,
S15, S16).

Finally, the current detected peak level p2 is smoothed in the time direction to obtain a peak level P representing a dynamic range (S12).

The smoothing in the time direction is performed by a recursive filter process, so that the stability of the peak level P and the accuracy improvement by the arithmetic processing can be obtained.

The microcomputer 4 uses the peak level P obtained as described above to calculate the gradation correction characteristic in the same manner as in the first or second embodiment.

The operations other than the detection of the dynamic range are the same as those in the first or second embodiment, and will not be described here.

As described above, in the third embodiment, the peak level can be detected from the histogram data obtained from the histogram detecting means without using the peak detecting circuit.

The effect of the present embodiment is to reduce the number of peak detection circuits by using the histogram data detected by the histogram detection means as the dynamic range information obtained by the dynamic range detection means.

(Embodiment 4) Hereinafter, a gradation correcting apparatus according to Embodiment 4 of the present invention will be described with reference to the drawings.

In the camera signal processing, the low-luminance portion is emphasized by gamma correction or the like, which greatly affects the entire screen such as a sense of resolution. However, the frequency of the low-luminance portion is small due to the histogram equalization, so that the low-luminance portion is emphasized. When the gain is suppressed, the resolution of the entire screen may be degraded, or the brightness of the entire screen may be reduced.

In the fourth embodiment, the sense of resolution of the entire screen,
A gradation correction device capable of storing the brightness of the entire screen will be described.

In the fourth embodiment, the configuration of the tone correction device and the algorithm up to the second normalization processing in the microcomputer 4 are the same as those in the first embodiment, and therefore are omitted, and the second MAX and MIN clip processing (S5 ) Will be described.

The microcomputer 4 limits the slope of each of the divided levels to the second MAX, M for the histogram data Hnorm2 (n) after the second normalization processing.
The IN clip processing (S5) is performed.

In the fourth embodiment, the second MAX, MIN
The operation of the clipping process is the same as that of the first, second or third embodiment. However, in the fourth embodiment, the maximum value and the minimum value of MAX (n) and MIN (n) are changed according to the division level.

FIG. 11A shows the clip value M of each division level.
AX (n) and MIN (n) are shown. The clip value of each division level shown in FIG. 11A is set such that it increases as the clip value of the low-brightness part increases, and MAX
(n) and MIN (n) are set to be smaller.

FIG. 11B shows the gradation correction characteristics. Figure 1
In FIG. 1B, the gradation correction characteristic at the maximum inclination is MAX, and the gradation correction characteristic at the minimum inclination is MIN.

The gradation correction characteristic output from the microcomputer 4 has a characteristic between MIN and MAX in FIG. 11B.

As can be seen from FIG. 11B, the gradation correction characteristic in the present embodiment is such that the inclination of the low luminance part becomes steep and the inclination of the high luminance part becomes gentle.

As described above, by reducing the control range of the gain of the division level of the low luminance section, the resolution of the entire screen and the brightness of the entire screen are preserved.

The operation after the gradation correcting means 5 is the same as that of the first embodiment.
Therefore, the description is omitted here.

The effect of this embodiment is that the resolution of the entire screen and the brightness of the entire screen can be preserved by reducing the control range of the gain of the division level of the low luminance section.

As described above, according to the present embodiment, even when the dynamic range is low, the optimum gradation correction characteristic can be obtained without suppressing the gradation correction characteristic.

According to the present embodiment, when the dynamic range of the input signal is smaller than the predetermined value, the gradation correction characteristic calculating means determines from the dynamic range information detected by the dynamic range detecting means. By fixing the gradation correction characteristic, an optimum gradation correction characteristic can be obtained without suppressing the gradation correction characteristic even when the dynamic range is low.

Further, according to the present embodiment, the peak detection circuit can be reduced by using the histogram data detected by the histogram detection means as the information of the dynamic range detected by the dynamic range detection means. .

Also, according to the present embodiment, the resolution of the entire screen and the brightness of the entire screen can be preserved by reducing the control range of the gain of the division level of the low luminance section.

Note that the peak detection circuit 2 of the present embodiment is an example of the dynamic range detecting means of the present invention, and the microcomputer 4 of the present embodiment is an example of the gradation correction characteristic calculating means of the present invention. The slope of the present embodiment is an example of a slope which is a ratio of a change amount of an output signal to a change amount of a level of an input signal in the gradation correction characteristic of the present invention.

A medium carrying a program and / or data for causing a computer to execute all or a part of the functions of all or a part of the tone correcting apparatus of the present invention, and which can be processed by the computer. The medium characterized by the above also belongs to the present invention.

Further, an information aggregate characterized by being a program and / or data for causing a computer to execute all or a part of the functions of all or a part of the tone correcting device of the present invention is also described. Belongs to the invention.

Further, the data of the present invention includes a data structure, a data format, a data type, and the like. The medium of the present invention includes a recording medium such as a ROM, a transmission medium such as the Internet, and a transmission medium such as light, radio waves, and sound waves. The medium carried by the present invention includes, for example, a recording medium on which a program and / or data is recorded, a transmission medium for transmitting the program and / or data, and the like.
In addition, the term “processable by the computer” of the present invention means that it can be read by a computer if it is a recording medium such as a ROM, and if it is a transmission medium, it can be a program and / or a program to be transmitted. Or that the data can be handled by a computer as a result of the transmission. The information aggregate of the present invention includes, for example, software such as a program and / or data.

Further, a program for causing a computer to execute all or some of the functions of all or some of the blocks, means, and circuits of the tone correction apparatus according to any of the above embodiments. The program recording medium on which the program and / or data is recorded may be a computer readable medium, and the read program and / or data may be a program recording medium that executes the function in cooperation with the computer.

[0124]

As is apparent from the above description, the present invention provides a gradation display device, a medium, and information which do not produce an unnatural image even if gradation processing is performed on various signals having different dynamic ranges. Aggregates can be provided.

Further, according to the present invention, there is provided a gradation correction apparatus, a gradation correction method, and a gradation correction method which do not suppress a gradation to a necessary part even when a gradation correction is performed when a dynamic range is smaller than a predetermined value. Media and information aggregates can be provided.

Further, according to the present invention, as a dynamic range detecting means, a gradation correcting apparatus and a gradation correcting method which do not require a peak detecting circuit for detecting a peak level of an input signal,
Media and information aggregates can be provided.

Further, the present invention can provide a gradation correction device, a gradation correction method, a medium, and an information aggregate that do not deteriorate the resolution of the entire screen.

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating a configuration of a tone correction device according to a first embodiment.

FIG. 2 is a flowchart of a tone correction characteristic calculation algorithm in a microcomputer 4 of the tone correction device according to the first embodiment;

FIG. 3 is a characteristic diagram illustrating histogram data and gradation correction characteristics of the gradation correction device according to the first embodiment.

FIG. 4 is a characteristic diagram illustrating a relationship between a peak level and a clip value MIN (n) of the gradation correction device according to the first embodiment.

FIG. 5 is a characteristic diagram illustrating histogram data and gradation correction characteristics of the gradation correction device according to the first embodiment.

FIG. 6 is a characteristic diagram illustrating a gradation correction characteristic of the gradation correction device according to the first embodiment.

FIG. 7 is a characteristic diagram illustrating a relationship between a peak level and a clip value MIN (n) of the tone correction device according to the second embodiment.

FIG. 8 is a characteristic diagram illustrating histogram data and gradation correction characteristics of the gradation correction device according to the second embodiment.

FIG. 9 is a configuration diagram illustrating a configuration of a gradation correction device of the gradation correction device according to the third embodiment.

FIG. 10 is a flowchart of a peak level detection algorithm in the microcomputer 4 of the gradation correction device according to the third embodiment.

FIG. 11 is a characteristic diagram showing histogram data and gradation correction characteristics of the gradation correction device according to the fourth embodiment.

FIG. 12 is a configuration diagram showing a configuration of a conventional gradation correction device.

FIG. 13 is a characteristic diagram showing histogram data and gradation correction characteristics of a conventional gradation correction device.

[Explanation of symbols]

 1. . . 1. input terminal; . . 2. a peak detection circuit; . . 3. histogram detection means; . . Microcomputer, 5. . . 6. tone correction means; . . 7. division level setting register; . . 8. comparator, . . Output terminal, 10. . . 10. signal level determination circuit; . . Multiplexer, 12. . . Register, 13. . . selector,

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Masayuki Yoneyama 1006 Kazuma Kadoma, Kadoma-shi, Osaka Matsushita Electric Industrial Co., Ltd. F-term (reference) 5C021 PA77 PA78 XA03 XA14 XA34 YC04 5C022 AB19 AB68 AC69 AC79

Claims (9)

[Claims] A dynamic range detecting means for detecting information on a dynamic range of an input signal; and a histogram data which divides the input signal into a plurality of division levels in a signal level direction and which is an appearance frequency of a signal for each division level. A tone correction characteristic calculating means for calculating a tone correction characteristic of a signal for each of the division levels based on the detected histogram data and information on the detected dynamic range; and A tone correction unit that performs tone correction on the input signal based on the calculated tone correction characteristic. 2. The gradation correction characteristic calculating means according to claim 1, wherein the gradient, which is a ratio of a change amount of the output signal to a change amount of the level of the input signal, in the gradation correction characteristic, Calculating the gradation correction characteristic by associating the obtained inclination with a signal appearance frequency, limiting the obtained inclination to a predetermined range, and changing the obtained inclination restriction range according to the information of the dynamic range. The tone correction device according to claim 1, wherein: 3. The gradation correction characteristic calculation means, wherein the gradation correction characteristic is not changed when the dynamic range is smaller than a predetermined value.
5. The gradation correcting device according to 1. 4. The dynamic range detecting means according to claim 1, wherein said dynamic range detecting means obtains information on said dynamic range based on a highest division level of said histogram data in which said input signal is distributed. 5. The gradation correcting device according to 1. 5. A histogram detecting unit that divides an input signal into a plurality of division levels in a signal level direction and detects histogram data that is a frequency of appearance of a signal for each division level, based on the detected histogram data. A tone correction characteristic calculating unit that calculates a tone correction characteristic of a signal for each of the division levels; and a tone correction unit that performs tone correction on the input signal based on the calculated tone correction characteristic. Wherein the gradation correction characteristic calculating means calculates a gradient of a ratio of a change amount of an output signal to a change amount of a level of an input signal in the gradation correction characteristic, for each of the division levels, the slope of the signal of the histogram data. Controlling the slope of the gradation correction characteristic for each of the division levels within a predetermined range, and controlling the gain of the division level of the low luminance portion Gradation correction apparatus characterized by a smaller circumference. 6. The division level of the low luminance portion,
6. The gradation correcting device according to claim 5, wherein a gain of a division level of the lowest luminance portion is fixed. 7. A gradation correction characteristic is calculated based on information on a dynamic range of an input signal and histogram data which is a frequency of appearance of a signal for each division level obtained by dividing the input signal into a plurality of levels in a signal level direction. And performing a tone correction on the input signal based on the calculated tone correction characteristics. 8. A medium carrying a program and / or data for causing a computer to execute all or a part of the functions of all or a part of the tone correction device according to claim 1. A medium which can be processed by a computer. 9. A program and / or data for causing a computer to execute all or a part of the functions of all or a part of the tone correction device according to claim 1. Information aggregate to be characterized.