JPH11331597A - Gradation correcting device of image pickup device and gradation correcting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gradation correcting device capable of executing the optimum reproduction of gradation with respect to various subjects. SOLUTION: The gradation correcting device of an image pickup device dividing an inputted image into plural areas, executing gradation correction for each area and synthesizing images gradation-corrected in each area to output is provided with a detecting means 11 dividing the inputted image into plural blocks to detect the average luminance of each block and a picture dividing position calculating means 10 calculating a picture dividing position from detected average luminance data of each block. Since picture division adapted to a subject condition can be executed, the optimum reproduction of gradation is possible.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for correcting gradation of an image such as a video camera and a method for correcting the same.
In particular, an optimum gradation correction effect is obtained according to the situation of the subject.

[0002]

2. Description of the Related Art A gradation correcting device of an image pickup device corrects a video signal so that the luminance of a reproduced image corresponds to the luminance of a subject. Until now, in order to effectively use an image receiving apparatus having a small dynamic range, various measures have been taken for this gradation correction.

[0003] A conventional image pickup device having a tone correction device is as follows.
As shown in FIG. 5, an image sensor 1 for alternately outputting two types of video signals having different exposure amounts within one field period, a preprocessing unit 2 for amplifying the video signals, and converting an analog video signal into a digital signal. A / D converter 3 for conversion, time axis converter 4 for aligning and separating two types of video signals having different exposure amounts and outputting the separated signals, and level synthesizing means 5 for synthesizing the two types of video signals A histogram data detecting means 8 for detecting a histogram of the luminance of the synthesized image signal; a microcomputer 10 for calculating the gradation characteristics based on the histogram; and a screen divided into four fixed areas. Gradation correction means 6 for performing gradation correction in accordance with the set gradation characteristics, region division pulse generation means 9 for dividing the combined image signal into four regions and outputting control pulses for combination, It has and a region combining unit 7 for synthesizing the gradation-corrected image for each area.

In this device, an image pickup device 1 is a horizontal CCD.
Is performed at twice the normal transfer speed, and two types of video signals, a video signal with a long exposure and a video signal with a short exposure, are alternately output within one field period. The output video signal is subjected to pre-processing 2 such as CDS and AGC,
The digital signal is converted into a digital signal by the A / D converter 3, and the long-time exposure image signal (Slong) and the short-time exposure image signal (Sshor) at standard speed and at the same timing are converted by the time axis converter 4.
t) and these signals are separated by the level synthesizing means 5
Are combined at a predetermined luminance level.

[0005] The area dividing pulse creating means 9 generates a screen dividing control pulse for dividing the screen into four fixed areas and synthesizing the same, and outputs the generated pulse to the histogram data detecting means 8 and the area synthesizing means 7.

The histogram data detecting means 8 detects the histogram of the composite image signal (Smix) output from the level synthesizing means 5 one region at a time for each field by the screen division position control pulse, and detects the detection result by the microcomputer 10. Output to The histogram is mx
It shows how many pixels having a certain gradation level exist in the n-point pixels.

The microcomputer 10 takes in histogram data of four regions in four fields, and for example,
A gradation characteristic is calculated for each region such that the higher the frequency of the histogram is, the more the contrast is enhanced, and the calculation result is set in the gradation correction means 6 corresponding to each region.

The tone correcting means 6 performs tone correction on the composite image signal of each of the areas A, B, C, and D so as to realize the tone characteristics set by the microcomputer 10. The signals Sa, Sb, Sc, and Sd are output. The area synthesizing means 7 synthesizes the image signal at a position determined by the screen division control pulse and outputs the synthesized image signal.

As described above, the conventional tone correction device divides the screen into four fixed areas and performs the most appropriate tone correction on the image signal in each area in that area, thereby providing the tone correction. The effect is enhanced.

[0010]

However, in the conventional gradation correction device, since the division position of the region to be subjected to gradation correction is fixed, the subject from high luminance to low luminance exists in the same region. In the case of subject conditions, there is a problem that effective gradation correction cannot be performed.

The present invention solves such a conventional problem. By controlling the screen division position in accordance with the subject conditions, it is possible to perform optimal gradation reproduction for various subjects. It is an object of the present invention to provide a gradation correction device and a gradation correction method.

[0012]

Therefore, the tone correcting apparatus of the present invention is configured to change the area to be divided on the basis of the luminance distribution of the input image.

Further, in the gradation correction method of the present invention, the input image is divided into a plurality of blocks, the average luminance of each block is detected, and the division position of the region is determined based on the distribution of the high luminance blocks having the high average luminance. Is set.

Therefore, it is possible to divide the screen into regions adapted to the conditions of the subject, and to perform optimal gradation correction on the image in each region.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention divides an input image into a plurality of regions, performs gradation correction for each region, and synthesizes a gradation-corrected image for each region. In a gradation correction device of an image pickup device that outputs a divided image, the region to be divided is changed based on the luminance distribution of the input image, and the screen can be divided according to the subject condition.

According to a second aspect of the present invention, an input image is divided into a plurality of blocks, a detecting means for detecting an average luminance of each block, and a screen division position is calculated from the detected average luminance data of each block. Screen division position calculation means is provided, the input image is divided into blocks, and the screen is divided so that the distribution of high-luminance blocks is included in one region.

According to a third aspect of the present invention, there is provided an image pickup apparatus which divides an input image into a plurality of regions, performs gradation correction for each region, and combines and outputs a gradation-corrected image for each region. In the gradation correction method, an input image is divided into a plurality of blocks, an average luminance of each block is detected, and a division position of an area is set based on a distribution of high luminance blocks having a high average luminance. Yes, it is possible to divide the screen into regions adapted to the subject conditions, and perform optimal gradation correction on the image in each region.

According to a fourth aspect of the present invention, when the distribution of the high-luminance blocks is in contact with any of the four sides of the screen,
The screen is divided into four regions, and the distribution of the high-luminance blocks is included in one of the regions. When the distribution of the high-luminance blocks is isolated at the center of the screen, the screen is divided into the central region and other regions. Is divided into two regions, and the distribution of the high-luminance blocks is included in the central region.
The number of regions to be divided is changed according to the position of the high-luminance block on the screen to enhance the gradation correction effect.

Hereinafter, an embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG.

As shown in FIG. 1, an image pickup apparatus provided with a gradation correction apparatus according to an embodiment of the present invention comprises an image pickup element 1 which alternately outputs two kinds of video signals having different exposure amounts within one field period. A pre-processing unit 2 for amplifying the video signal and an A / D converter 3 for converting an analog video signal into a digital signal
And align the time axes of two types of video signals with different exposure amounts,
A time axis converter 4 for separating and outputting, a level synthesizing means 5 for synthesizing the two types of video signals, and a synthesized image signal (S
histogram data detecting means 8 for detecting a histogram of the luminance of the mixed image, block data detecting means 11 for dividing the synthesized image signal (Smix) into 8 × 6 blocks and detecting the average luminance of each block, and block data detecting means. A microcomputer 10 that determines a screen division position based on the average luminance of each block output from 11 and calculates a gradation characteristic in each of the divided regions of the screen, and a microcomputer 10 for each region according to the gradation characteristic set for each region. Gradation correction means 6 for performing gradation correction of an image, area division pulse generation means 9 for outputting a control pulse for dividing and synthesizing an area of a composite image signal according to a screen division position determined by the microcomputer 10, An area synthesizing means 7 for synthesizing an image whose gradation has been corrected for each area is provided.

In this apparatus, the operation until the level synthesizing means 5 outputs the synthesized image signal (Smix) is the same as that described in the conventional apparatus.

The block data detecting means 11 is shown in FIG.
As shown in FIG. 3, the synthesized image signal (Smix) output from the level synthesizing means 5 is divided into 48 blocks in the horizontal direction 8 and the vertical direction 6, and as shown in FIG. ave [i] [j] is calculated.

The calculated average luminance data of each block is input to the microcomputer 10, and the microcomputer 10 uses the average luminance data of each block to classify a region having a predetermined luminance level or higher from other regions. The division position data is created by a procedure described later.

The division position data is data indicating a horizontal position and a vertical position at which an area is switched. As shown in FIG. 4A, the screen is divided into four areas A, B, C, and D. In the case of division, Hstart indicating the horizontal division position by an arrow and Vs indicating the vertical division position by an arrow
tart is division position data. Note that this start indicates that in the case of horizontal division position data, when moving to the right, switching from a low-luminance area to a high-luminance area is performed, and in the case of vertical division position data, Indicates that when moving downward, the area is switched from a low luminance area to a high luminance area. FIG.
In (a), the brightness of the region D is high.

Conversely, when switching from a high brightness area to a low brightness area, Hend and Vend are displayed. FIG.
(B) shows a case where the screen is divided into two regions, a high-luminance region D and another low-luminance region. In this case, the horizontal division position data indicates the boundary of the region D. The indicated Hstart and Hend and the vertical division position data are Vstart and Vend.

The division position data Hstart, Hend, Vstart, Vend created by the microcomputer 10 are input to the area division pulse creating means 9. Region dividing pulse creating means 9
Receives this, as shown in FIGS. 4A and 4B,
0 to 1 corresponding to division position data of start and Vstart
, And the division pulse Hpul gradually changes from 1 to 0 in accordance with the division position data of Hend and Vend.
s and Vpuls are generated and output to the histogram data detecting means 8 and the area synthesizing means 7.

The histogram data detecting means 8 detects the histogram data of the composite image signal (Smix) one region at a time for each field by using the divided pulses, and outputs it to the microcomputer 10. When the screen is divided into four regions (FIG. 4A), the microcomputer fetches the histogram data for four regions in four fields and calculates the optimum gradation characteristics corresponding to each of the four regions. Is set in the corresponding gradation correction means 6.

The gradation correcting means 6 performs gradation correction on the input composite image signal (Smix) for realizing the gradation characteristics set for each area, and processes the processed signal Sa. , Sb, Sc, and Sd are output to the area combining means 7. The area synthesizing means 7 synthesizes the signals Sa, Sb, Sc, and Sd according to the divided pulses, and outputs Sout. This output Sout
Is given by (Equation 1).

Sout = (1-Hpuls) / (1-Vpuls) / Sa + Hpuls / (1-Vplus) / Sb + Vpuls / (1-Hplus) / Sc + Hpuls / Vplus / Sd (Equation 1) Divided pulse Is gradually changed at the position of the division position data in order to smoothly combine the boundaries of the respective regions.

Further, depending on the subject condition, the distribution of the high-luminance blocks may be isolated at the center. In such a case, as shown in FIG.
B and C are divided into a combined area and a D area. The gradation characteristics of each area are calculated from the histogram data of the two areas, and the divided floor area is divided into a central D area and other areas. Perform key correction.

The combined output Sout at this time is obtained by applying a signal obtained by subjecting the combined image signal (Smix) to gradation correction set in the D region to Sd, and performing gradation correction set in regions other than the D region. Let the signal obtained as S ′ be given by (Equation 2).

Sout = (1-Hpuls) · (1-Vpuls) · S ′ + Hpuls · (1-Vplus) · S ′ + Vpuls · (1-Hplus) · S ′ + Hpuls · Vplus · Sd (Equation 2) Next, a procedure for creating division position data from the average luminance data of each block will be described.

The creation of the division position data is performed according to the flowchart of FIG.

Step 1: i = 0,1,
2, .., 7, and j = 0,1, .., 5 in the vertical block,
First, the average luminance data ave [i] of each input block
[j] is sequentially compared with a certain threshold value sat, and a block exceeding the threshold value sat is set as a high-luminance block, and a flag of flat_sat [i] [j] = 1 is set. FIG. 3C shows a state where flag_sat [i] [j] is set to 1 in the high luminance block.

Step 2: Next, the smoothing filter shown in FIG. 3D is used for this flag to perform a moving smoothing filter process. At this time, if the moving smoothing filter processing is directly performed on the data of FIG. 3C, the end portions (i = 0, 7, j = 0,
Since the information of 5) is lost, the flag value of the block at the end is arranged outside of it, so that flag_sat [i] [j] for 8 in the horizontal direction and 6 in the vertical direction remains even after smoothing. The flag value of each block after the moving smoothing filter processing is as shown in FIG.

Step 3: This smoothed flag_sat
[i] [j] are added in the horizontal and vertical directions according to (Equation 3) and (Equation 4) to obtain sums Hsum [i] and Vsum [j].

Hsum [i] = Σflag_sat [i] [j] (i = 0 to 7, j = 0 to 5) (Equation 3) Vsum [j] = Σflag_sat [i] [j] (i = 0 to 7 , j = 0 to 5) (Equation 4) Next, the average value of the horizontal addition value Hsum [i] and the average value of the vertical addition value Vsum [i] are obtained. The thresholds are set to Hth and Vth.

Step 4: Next, the thresholds Hth, Vth and the added values Hsum [i], Vsum [j] are sequentially compared, and flag_Hsum [i] = 1, flag_Vsum [j The flag of] = 1 (split pulse flag) is set. As a result, a flag is set in a column of a block including many high-luminance blocks.

Step 5: If tone correction is performed with a tone characteristic different from the surroundings in an extremely small area, an uncomfortable image is obtained. Therefore, the changing condition of the divided pulse flag is defined. For example, when the divided pulse flag is set only in one block, the flag is lowered (divided pulse flag shaping process).

Step 6: The number of times the shaped divided pulse flag changes from 0 to 1 or 1 to 0 determines whether the screen is divided into four regions or two regions. Dividing position data is calculated using the changing boundary as a dividing position.

Here, when the number of changes of the horizontal and vertical divided pulse flags is both once or only one is up to two, the screen is divided into four regions, and the divided pulse flag is If both changes are two,
Divide into two regions. This means that both changes are 1
If only one or two times, the distribution of the high-brightness block is in contact with any of the four sides of the screen, and
This is because effective gradation correction can be performed by dividing into two. In addition, in the case of both times, the subject condition is that the distribution of the high-luminance blocks is isolated at the center.
Splitting into two areas is more than splitting into two areas.
This is because more natural gradation correction can be performed.

When the number of changes of the division flag is three or more, since the number of screen divisions is four,
The screen is divided into four regions with the center in the vertical direction as a dividing position, and gradation correction is performed.

As described above, the gradation correcting apparatus of the present invention automatically divides the screen into a plurality of regions according to the subject conditions, and performs the optimum gradation correction for each region. The data of each area that has been processed is synthesized.

[0044]

As is apparent from the above description, the gradation correcting apparatus of the present invention automatically divides the screen area according to the brightness of the image and performs the optimum gradation correction for each area. ing. Therefore, it is possible to obtain an optimum gradation correction effect corresponding to various subjects.

Further, the gradation correction method of the present invention enables the area of the screen to be divided according to the subject conditions, and can enhance the effect of gradation correction.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a solid-state imaging device including a gradation correction device according to an embodiment of the present invention;

FIG. 2 is a flowchart showing a gradation correction method according to the present invention;

3A and 3B are schematic diagrams illustrating a gradation correction method according to the present invention, in which FIG. 3A illustrates a captured input image and the position of a block, FIG. 3B illustrates average luminance data of each block,
(C) A diagram showing a block detected as a high-luminance block,
(D) a characteristic diagram of a smoothing filter, (e) a diagram showing a method of calculating a division position from a high-luminance flag after smoothing,

FIGS. 4A and 4B are diagrams showing a correspondence relationship between a screen division pulse and each region in the gradation correction device of the present invention, wherein FIG. 4A shows a case where a screen is divided into four regions, and FIG. Diagram showing the case of dividing into regions,

FIG. 5 is a configuration diagram of a solid-state imaging device including a conventional tone correction device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image sensor 2 Pre-processing part 3 A / D converter 4 Time axis converter 5 Level synthesizing means 6 Gradation correcting means 7 Area synthesizing means 8 Histogram data detecting means 9 Area dividing pulse creating means 10 Microcomputer 11 Block data detecting means

Claims (4)

[Claims] 1. A gradation correction device for an image pickup apparatus, which divides an input image into a plurality of regions, performs gradation correction for each region, and combines and outputs a gradation-corrected image for each region. A gradation correction apparatus, wherein the region to be divided is changed based on a luminance distribution of an image. 2. A detecting means for dividing the input image into a plurality of blocks and detecting an average luminance of each block, and a screen dividing position calculating means for calculating a screen dividing position from the detected average luminance data of each block. The gradation correcting apparatus according to claim 1, further comprising: 3. A gradation correction method for an image pickup apparatus, which divides an input image into a plurality of regions, performs gradation correction for each region, and combines and outputs an image subjected to gradation correction for each region. A gradation correction method comprising: dividing an image into a plurality of blocks; detecting an average luminance of each block; and setting a division position of the region based on a distribution of the high luminance blocks having a high average luminance. 4. When the distribution of the high-luminance blocks touches any one of the four sides of the screen, the screen is divided into four regions, and one of the regions includes the distribution of the high-luminance blocks, When the distribution of the high-luminance blocks is isolated at the center of the screen, dividing the screen into two regions, a central region and another region, and including the distribution of the high-luminance blocks in the central region. 4. The gradation correction method according to claim 3, wherein: