JPH03245277A - Contrast extraction filter - Google Patents

Abstract

PURPOSE:To extract the contrast of a central picture element from difference between the central luminance value of an outer box (OB) and the luminance value of an inner box (IB) and to improve the roundness of an edge by separating the IB and the OB for the (l) and (m) number of picture elements respectively. CONSTITUTION:The IB and the OB are arranged while being separated for the (l) and (m) number of picture elements respectively. Picture data to be inputted is supplied to a central calculation part 6 in addition to shift registers 1-5. The shift registers 1-5 supply the five data of luminance values x1-2j-2, xi+2j-2, xi-2j+2 and xi+2j+2 of four adjacent picture element data to the calculation part 6 in the same time state for each liminance value xij of the picture data to be inputted with this luminance value as the central picture element. The calculation part 6 calculates a central value M from the five picture element data and this value M shows the central luminance of the OB. A latch circuit 9 latches the xij to be outputted from the register 2 and supplies it to a subtracter 7, and the subtracter 7 subtracts the central value M from the luminance value xij of the IB and supplies the value of xij -M to an arithmetic part 8. Then, the arithmetic part 8 extracts the contrast from the absolute value and outputs the contrast.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a contrast extraction filter, and particularly to a contrast extraction filter for extracting local contrast of a moving image in real time.

[Conventional technology]

Conventionally, as this type of contrast extraction technique, there is a contrast box shown in FIG. 4. This consists of an inner box and an outer box circumscribing the inner box, and the contrast of the center pixel of the box is determined by the absolute value of the difference in average luminance between the two boxes.

In an area expressed by an image scanning array for each frame of image data, an inner box 18 for targeting objects, etc., is set in an outer box 17 containing full-screen elements, circumscribing the outer box 17, and as described above. Thus, the absolute value of the average luminance difference between both boxes is taken as the contrast of the center pixel of the box.

In FIG. 4, μ. If UT is the average brightness of the pixels in the outer box 17 and μ0 is the average brightness of the pixels in the inner box 18, then the contrast xlj of the center pixel Xll is 1 μmN−μ. Denoted by UT l. In addition, X
11 indicates the center pixel.

[Problem to be solved by the invention]

In the conventional contrast box described above, the contrast value corresponds very sensitively to the box size, so in order to obtain faithful contrast, a priori information about the box size is required, and the box size cannot be selected optimally. Even when the image is captured, the disadvantage is that the contours, or so-called edges, of the target included in the image are dulled.

SUMMARY OF THE INVENTION An object of the present invention is to provide a contrast extraction filter that eliminates the above-mentioned drawbacks and significantly improves edge rounding.

[Means to solve the problem]

The contrast extraction filter of the present invention includes an inner box, and p and m in the horizontal and vertical directions, respectively, from the inner box without circumscribing the inner box.
Based on the absolute value of the difference between the median luminance value of the pixels included in the inner box and the median luminance value of the pixels included in the outer box, for a contrast box having an outer box set at a position separated by a pixel. The image forming apparatus is configured to include means for extracting the contrast of a central pixel in the contrast box.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of a contrast extraction filter of the present invention. The embodiment shown in FIG. 1 includes shift registers 1 to 5, a median value calculation section 6, a subtracter 7, an absolute value calculation section 8, and a latch circuit 9.

Before explaining the embodiment based on FIG.
First, the basic concept of the present invention will be explained.

FIG. 2 is a conceptual diagram of the present invention, showing an inner box 11 set as a unit pixel and this inner box 11.
The basic feature is that the outer box 10 is located at a distance of ρ1m pixels without being circumscribed by the outer box 10, thereby significantly suppressing the rounding of edges.

In this case, if X(II) is the median value of the outer box 10, then the center pixel is created. Therefore, the median value X(II) of the outer box IO is calculated, and the brightness value X of the inner box
, , , for all pixels, contrast information can be obtained.

Returning again to FIG. 1, the description of the embodiment will be continued.

The input image data is supplied to the shift registers 1 to 5 as well as to the median calculation unit 6. These shift registers are
For each luminance value Xi of input pixel data, the luminance value X +-2j-z of adjacent 4 pixel data with this as the center pixel
+ X +→1j-2+ X 1-21+21 X
This provides a time delay for supplying I→2j+205 data to the median calculation unit 6 in the same time state.

Therefore, processing is started after these five pixel data are input. However, among each pixel data mentioned above,
Luminance value of the temporally slowest pixel data X l+21+2
Since we apply a time delay based on
is supplied as is to the median value calculation unit 6.

FIG. 3 is an explanatory diagram of the pixel arrangement in the embodiment of FIG. 1. As shown in FIG. 3, the brightness value X11 of pixel 12 at a certain time is used as the center pixel, pixel 15.16 is the latest and therefore the slowest vertical scanning data, and pixel 13.14 is the data from the previous one. It is assumed that pixels 14 and 16 are at the same time position in the horizontal direction. In this state, if a delay corresponding to each pixel position is applied based on the luminance value XN41+2 of the temporally slowest pixel data among the five pixel data, all pixel data will be in the same time state and the median value calculation unit 6 will be supplied. In this example, each pixel is shifted by two horizontal scans (2HD) in the vertical direction and by two pixel scans (2D) in the horizontal direction, so shift registers ~5 are shifted by 4D, 2D, 2HD, and 4HD, respectively. , the data is shifted to give a shift amount of 4D. The symbols within the blocks of shift registers 1 to 5 in FIG. 1 correspond to the delay amounts of the above-mentioned 4D, 2D, etc.

Returning again to FIG. 1, the description of the embodiment will be continued.

The median value calculation unit 6 calculates a median value indicating the center value of the brightness of the five pixel data thus provided. This median value M is expressed by the following equation (1). This M is outer box 1
This indicates a central brightness value of 0.

M=MID (XI-H-21XI-21+21X +
j+ X I+21-21 X l+21+2)...
(1) The latch circuit 9 latches Xlj output from the shift register 2 and supplies it to the subtracter 7.

A subtracter 7 subtracts the median value M output from the median value calculation unit 6 from the luminance value Xlj of the inner box, and obtains X,.

-M is supplied to the absolute value calculation unit 8.

The absolute value calculation unit 8 takes the absolute value of the following equation (2) and calculates △ This Xlj is output as a filter output.

Δ x ,, = l x ,, −M l
(2) This filter output Xl+ is the difference between the center luminance value of the outer box 10 and the luminance value (X,,) of the inner box shown in FIG. 2, and there is a spatial difference between the two boxes. Since the images are separated and have no correlation, they are output as high-quality contrast information with no rounded edges.

〔Effect of the invention〕

As explained above, the present invention has a structure in which the inner box and the outer box are separated from each other by 12 m, and the central brightness value of the outer box and the brightness value
By contrasting the difference with 1, IXI~(ρ
This has the effect of being able to extract only local contrast having a size up to +1)X (m+1) faithfully to the acquired image without smoothing the edges near the boundaries of both boxes.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the contrast extraction filter of the present invention, FIG. 2 is a conceptual diagram of the contrast extraction filter of the present invention, and FIG. 3 is an explanatory diagram of the pixel arrangement in the embodiment of FIG. FIG. 4 is an explanatory diagram of a conventional contrast box. 1 to 5...Shift register, 6...Median value calculation unit, 7...Subtractor, Death...Absolute value calculation unit, 9...・Latch circuit, 10.17...
...Outer box, 11.18...Inner box, 12-16...pixels.

Claims (1)

[Claims] For a contrast box that has an inner box and an outer box that does not circumscribe the inner box and is set horizontally and vertically apart from the inner box by l and m pixels, the pixels included in the inner box are A contrast extraction filter comprising: means for extracting the contrast of a central pixel in the contrast box based on the absolute value of the difference between the central brightness value of the outer box and the central brightness value of the pixels included in the outer box.