JPH0591372A - Flicker suppressing method - Google Patents

Abstract

PURPOSE:To suppress flicker by detecting a part having a large difference from lightness between adjacent lines of an image and revising the lightness of, e.g. a bright picture element. CONSTITUTION:A brightness difference. detection means 22 compares a brightness of a picture element through a 1 line delay means 21 with a brightness of a current picture element, inputs the difference to a threshold level detection means 23, and the relation of quantity of the brightness is inputted to a picture element revision means 24. A threshold level detection means 23 compares the difference from the brightness to be inputted with a threshold level TS and inputs the result to the picture element revision means 24. Then the picture element revision means 24 revises a picture element (in this case, brightness) depending on the result of detection of the threshold level detection means 23 and the brightness difference detection means 22 and applies interlacing the result and outputs it to a display device. Moreover, when the brightness is revised, it is the case that the difference between the result of detection of the threshold level detection means 23 and the brightness detected by the brightness difference detection means is larger than the threshold level TS and the brightness is revised when the brightness difference detection means 22 detects it larger.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for suppressing video image flicker.

[0002]

2. Description of the Related Art A method conventionally used as a method for suppressing flicker in a video image is a value (lightness, saturation, hue) of an arbitrary pixel in the image and a line adjacent to the upper and lower sides of the pixel. The sum of the corresponding pixel value of
The value of the sum and the value of the arbitrary pixel are weighted in advance and the pixel values are averaged.

By the way, according to such a conventional method, when a still image such as a figure or a character image is displayed as an image, the effect of suppressing the flicker becomes insufficient depending on how the coefficient for weighting is adopted, and the image is also displayed. However, there is a problem that the resolution of the image is significantly deteriorated.

There is also a method of suppressing flicker by changing white or pixels close to white vertically adjacent to black or pixels close to black in a black-and-white image image to gray, for example.

According to this method, it is possible to suppress the deterioration of the image resolution seen in the above-mentioned method, but since only the relationship of pixels in the vertical direction is determined, it is possible to detect the pixels in the oblique direction. Although there is not much flicker visually, there is a problem in that its brightness (luminance) decreases and it becomes difficult to see.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems of the prior art, and an object thereof is to provide a method for effectively suppressing flicker without reducing the resolution of an image. To do.

[0007]

The first invention of the present invention is as follows:
A step of obtaining a difference in pixel value between an arbitrary pixel and a pixel adjacent thereto by a luminance detecting means for detecting a luminance value of each pixel forming an image, and a threshold value preset for the obtained difference in pixel value And a step of changing the pixel value of a pixel having a larger pixel value among the above two pixels when the difference between the pixel values is larger than a threshold value.

A second aspect of the present invention is a step of detecting a pixel value of a target pixel by a pixel detecting means for detecting a pixel value of each pixel forming an image and comparing it with a preset first threshold value. And a step of detecting the brightness values of adjacent pixels vertically adjacent to the target pixel and comparing the brightness values with a preset second threshold value; and detecting pixel values of adjacent pixels adjacent to the left and right of the pixel to detect a third value. The method includes a step of comparing with a threshold value and a step of changing the pixel value of the target pixel based on the result of each step.

[0009]

In general, image flicker tends to occur when there is a large difference in brightness between adjacent lines in an image. On the other hand, even if the brightness of a dark pixel is changed, The effect of suppressing flicker is extremely small.

Even if the brightness difference between vertically adjacent pixels such as diagonal pixels is large, flicker is less likely to be felt when bright pixels are not continuous in the horizontal direction.

According to the first aspect of the present invention, a portion having a large difference in brightness between the lines adjacent to each other in the image is detected, and the brightness of, for example, a bright pixel is changed at that portion. As a result, it is possible to effectively suppress flicker without causing blurring in the image, that is, without substantially reducing the image resolution.

Further, according to the second aspect of the invention, for example, white or a pixel close to white in the image is detected, and at least one of pixels vertically adjacent to the pixel is black or a pixel close to black. Further, when at least one of the pixels adjacent in the left-right direction of the pixel is white or a pixel close to white, the brightness value of this pixel is changed so that the image is not blurred, that is, the image It is possible to effectively suppress flicker by preserving the pixel components in the diagonal direction with almost no reduction in resolution.

[0013]

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

FIG. 1 shows a process flow diagram disclosing the first inventive method. Here, it is assumed that there are M × N pixels, and the data for all the pixels of one frame is taken in at the start point of the figure. Further, a pixel is black and white data, and a luminance value which is a scale of lightness is considered as a pixel value.

First, in step 11, the pixel counters I and J are initialized and set to the first pixel position of the image.

Next, at step 12, the difference between the brightness value x (i, j) of the pixel (i, j) and the brightness value x (i, j + 1) of the corresponding pixel (i, j + 1) on the next line. Δx is calculated.

The difference Δx thus obtained is taken in step 13 as its absolute value | Δx |, and compared therewith with a preset threshold value Ts.

Results of comparison If the absolute value of the difference in luminance value | Δx
When | is smaller than the threshold Ts, the brightness value x (i,
In j), nothing is changed, and the process jumps to step 17, where the pixel counter I is updated by one.

Further, as a result of comparison, the absolute value of the difference between the brightness values | Δx
When | is larger than the threshold value Ts, the routine proceeds to step 14, where the brightness value x (i, j) and the brightness value x (i, j) are calculated.
+1) is compared and the larger luminance value is changed in steps 15 and 16.

When the change of the brightness value is completed in steps 15 and 16, the process proceeds to step 17 where the pixel counter I is updated by one.

After that, the above step 1 is performed until I reaches M.
When the processes from 1 to 17 are executed and the process for this I is completed, the pixel counter J
Is updated by one, and the processing from step 11 to step 18 is executed until N is reached for this J.

By the way, the pixel x in step 15
The luminance value x (i, j) of (i, j) is changed by the following equation 1.

[0023]

[Equation 1] Here, α is a preset constant and determines the flicker suppressing effect. That is, the smaller α is, the smaller the effect of suppressing flicker is. Further, if α is increased, the effect of suppressing flicker also increases, but in this case, the resolution of the image decreases. Therefore, as α, an appropriate value is selected within the range of 0 ≦ α <1.

In step 16, the brightness value x (i, j + 1) of the pixel (i, j + 1) is changed by the following equation 2 as in step 15.

[0025]

[Equation 2] An embodiment of an apparatus using the above flicker suppressing method is shown in FIG. In FIG. 2, 20 is a digital video input, 21 is a 1-line delay means, 22 is a brightness difference detection means,
Reference numeral 23 is a threshold value detecting means, 24 is a pixel value changing means, and 25 is an output.

The input 20 of the digital video is the input 1
It is input to the line delay unit 21, the brightness difference detection unit 22, and the pixel value changing unit 24.

The 1-line delay means 21 delays the input data by 1 line and stores it in a memory means such as a buffer (not shown), and this data is detected by the brightness difference detection means 2
2 and the pixel value changing means 24.

The brightness difference detecting means 22 compares the brightness value of the pixel passed through the 1-line delay means 21 with the brightness value of the current pixel (corresponding to step 12 in FIG. 1), and detects the difference between them by the threshold value detection. In addition to the input to the means 23, the magnitude relation of the brightness values is input to the pixel value changing means 24.

The threshold value detecting means 23 compares the difference between the brightness values input from the brightness difference detecting means 22 with the threshold value Ts (corresponding to step 13 in FIG. 1), and the result is the pixel value changing means 24. To enter.

The pixel value changing means 24 changes the pixel value (here, the luminance value) according to the result of the threshold value detecting means 23 and the result of the luminance difference detecting means 22, and interlaces the pixel value (not shown). Output to.

When the above-mentioned brightness value is changed, the result of the threshold value detecting means 23 is the case where the difference between the brightness values detected by the brightness difference detecting means 22 is larger than the threshold value Ts, and the brightness difference detecting means 22. However, the brightness value is changed.

Although the threshold value Ts and the value of the constant α depend on the characteristics such as the resolution of the display device used, the threshold value Ts
It has been found by simulation that substantially good results can be obtained by setting .alpha. To 1/2 of the maximum luminance value and .alpha. To 1/2.

Next, FIG. 3 shows a flow chart of a process which discloses the second invention method. Here, it is assumed that there are M × N pixels as in the method of the first invention, and the data for all the pixels of one frame is
Data is taken in at the start of the figure. Further, a pixel is black and white data, and a luminance value which is a scale of lightness is considered as a pixel value.

In step 31, the pixel counters I and J
Is initialized and set to the first pixel of the image.

Next, at step 32, the pixel (i, j)
Luminance value x (i, j) of is compared with a first threshold Tw.
Here, if the brightness value x (i, j) is not larger than the first threshold value Tw, the brightness value x (i, j) is not changed, and the process skips to step 38 and the pixel counter I or J is skipped.
Update one.

On the other hand, as a result of the comparison in step 32, if the brightness value x (i, j) is larger than the first threshold value Tw, the process proceeds to step 33, and the line immediately before the pixel (i, j) is detected. The luminance value x (i, j-1) of the corresponding pixel (i, j-1), that is, the pixel adjacent in the upward direction, is compared with the second threshold value Tb.

As a result of comparison, the luminance value x (i, j-1)
Is smaller than the second threshold Tw, the next step 3
4, the luminance value x (i, j + 1) of the pixel (i, j + 1) corresponding to the next line of the pixel (i, j), that is, the pixel adjacent in the downward direction is compared with the second threshold value Tb. To be done.

If the brightness value x (i, j + 1) is not smaller than the threshold value Tb, no change is made to the brightness value x (i, j + 1) and the process goes to step 38 to set the pixel counter I or J to one. One update.

As a result of the comparison in step 33 or step 34, the brightness value x (i, j-1) or x (i,
If j + 1) is smaller than the second threshold value Tb, the process proceeds to step 35, and the luminance of the pixel (i-1, j) immediately before the same line as the pixel (i, j), that is, the pixel adjacent in the left direction The value x (i-1, j) is compared with a third threshold value (here the same as the first threshold value) Tw.

If the luminance value x (i-1, j) is the third value,
If not larger than the threshold Tw of
Next pixel (i + 1, j) on the same line as pixel (i, j)
That is, the luminance value x (i + 1, j) of the pixel adjacent to the right is compared with the third threshold value Tw.

In step 36, the brightness value x (i + 1,
If j) is not larger than the third threshold value Tw, the luminance value x
(I + 1, j) is not changed, and the process jumps to step 38 to update the pixel counter I or J by one.

As a result of the comparison in step 35 or step 36, the brightness value x (i-1, j) or the brightness value x
If (i + 1, j) is larger than the third threshold value Tw, the process proceeds to step 37, where the luminance value x of the pixel (i, j) is x.
Change the value of (i, j).

The above processing is repeated while updating the pixel counters I and J in step 38, and is completed when the processing of this pixel M × N in all images is completed.

FIG. 4 shows an embodiment of an apparatus using the flicker suppressing method of the second invention.

In the figure, 40 is an input, 41, 43, 4
Reference numeral 4 is a 1-dot delay means, 42 and 45 are 1-line delay means, 51 to 55 are threshold value checking means, 46 is a pixel value changing means, and 47 is an output.

The input of the digital video is input through the input 40 and the data of the brightness value of one pixel is stored in the memory means such as a buffer (not shown) and the one dot delay means 41 and the data of the brightness value of the pixel of one line. Data is input to the 1-line delay means 42 which also stores it in a memory means such as a buffer (not shown).

The 1-dot delay means 41 sends the data of the memory means to the threshold value checking means 51, where the threshold value Tw is sent.
And the data are compared (corresponding to step 32 in FIG. 3).

The 1-line delay means 42 sends the data adjacent to the data of the 1-dot delay means 41 above to the threshold value inspection means 52, where it is compared with the threshold value Tb (see FIG. 3). Corresponding to step 33). The 1-line delay means 41 also sends the data to the 1-dot delay means 43.

The 1-dot delay means 43 saves one pixel of data adjacent to the data of the 1-dot delay means 41 for one pixel, and sends this to the threshold value inspection means 53, where it is used as the threshold value Tb. A comparison is made (corresponding to step 34 in FIG. 3). 1
The dot delay means 43 also stores the data adjacent to the left of the 1 dot delay means 41 and sends it to the 1 dot delay means 44, the 1 line delay means 45 and the pixel value changing means 46. 1-dot delay means 44 and 1-line delay means 45
Are adjacent to the left and right sides of the 1-dot delay means 41, respectively.
Data to threshold checking means 54 and 55, where each is compared to a threshold Tw.

The comparison result of each of the threshold value inspection means 51 to 55 is inputted to the pixel value changing means 46. The pixel value changing means 46 judges whether to change the luminance value of the pixel (i, j) based on the comparison result, and according to the result, with respect to the data input from the 1-dot delay means 43. , The luminance value is changed based on a preset rule, or is output without being changed.

In the second aspect of the invention, the threshold values Tw and Tb depend on the characteristics of the output display device, but Tw is 2/3 of the maximum brightness value, Tb is 1/5 of the maximum brightness value, and the brightness value is changed. It has been found from simulation results that flicker can be effectively suppressed by setting the change value of the pixel to be set to about ⅔ of the maximum luminance value.

[0052]

As described above, according to the present invention, the step of obtaining the difference between the pixel value of an arbitrary pixel and the pixel value adjacent thereto by the brightness detecting means for detecting the brightness value of each pixel forming an image, Comparing the obtained difference in pixel value with a preset threshold value, and changing the pixel value of a pixel having a larger pixel value among the two pixels when the difference in pixel value is larger than the threshold value. , Or a step of detecting the pixel value of the target pixel by a pixel detection means for detecting the pixel value of each pixel forming the image, and comparing the pixel value with a preset first threshold value; A step of detecting the brightness values of vertically adjacent adjacent pixels and comparing them with a preset second threshold value; and a step of detecting pixel values of adjacent pixels adjacent to the left and right of the pixel and comparing them with a third threshold value. , The target pixel based on the result of each step A step of changing the pixel values, without causing blurring in the image because those become more, i.e. Ime - it is possible to effectively suppress the flicker without decreasing mostly the di-resolution.

[Brief description of drawings]

FIG. 1 is a flow chart of processing showing a first invention method.

FIG. 2 is a block diagram of an apparatus using the second inventive method.

FIG. 3 is a flow chart of processing showing a second invention method.

FIG. 4 is a block diagram of an apparatus using the second inventive method.

[Explanation of symbols]

 22 Luminance Difference Detection Means 23 Threshold Detection Means 24, 46 Pixel Value Change Means 51-55 Threshold Inspection Means

Claims (2)

[Claims] 1. A step of obtaining a difference in pixel value between an arbitrary pixel and a pixel adjacent thereto by a pixel detecting means for detecting a pixel value of each pixel forming an image, and a difference between the obtained pixel values is calculated. A flicker suppressing method comprising: a step of comparing with a preset threshold value; and a step of changing a pixel value of a pixel having a larger pixel value among the two pixels when the difference between the pixel values is larger than the threshold value. 2. A step of detecting a pixel value of a target pixel by a pixel detection means for detecting a pixel value of each pixel forming an image and comparing the detected pixel value with a preset first threshold value, and above and below the target pixel. A step of detecting a pixel value of an adjacent pixel adjacent to the pixel and comparing it with a preset second threshold value; a step of detecting a pixel value of an adjacent pixel adjacent to the left and right of the pixel and comparing the pixel value with a third threshold value; A flicker suppressing method comprising the step of changing the pixel value of the target pixel based on the result of each step.