KR100769728B1 - Contrast enhancement apparatus using histogram and method thereof - Google Patents

Abstract

An apparatus and a method for improving contrast using histogram are provided to generate an output image having exact uniform density through smoothing and stretching methods based on the size of a neighboring histogram, thereby bringing the improvement of contrast. An apparatus for improving the contrast includes a histogram generator(310), an expansion part(320), the first calculation part(330), the second calculation part(340), and an output image generator(350). The histogram generator(310) generates a histogram showing the number of pixels for each brightness and the brightness. The expansion part(320) expands the generated histogram into an entire brightness area. The first calculation part(330) adds histograms adjacent to the histogram to each other and calculates the total sum of the histograms. The second calculation part(340) calculates the interval between adjacent histograms by dividing each histogram by the total sum of the histograms. The output image generator(350) moves each histogram into a position calculated by the second calculation part(340) to generate an output image.

Description

Contrast Enhancement Apparatus Using Histogram and Method etc.

1 is a block diagram of a histogram smoothing device according to the prior art.

2 to 5 are graphs showing histograms by histogram smoothing according to the prior art.

6 is a block diagram of a histogram stretching device according to the prior art.

Figure 7 is a graph showing the histogram by the histogram stretching method according to the prior art.

8 is a block diagram schematically showing a contrast enhancement apparatus using a histogram according to the present invention.

9 to 13 is a graph showing the histogram by the contrast enhancement device using the histogram according to the present invention.

14 is a flowchart schematically showing a contrast enhancement method using a histogram according to the present invention.

<Description of Symbols for Major Parts of Drawings>

300: contrast enhancement device 310: histogram generator

320: expansion unit 330: first operation unit

340: second calculator 350: output image generator

The present invention relates to an apparatus and method for improving a contrast using a histogram, and more particularly, to an apparatus and a method for improving the contrast of an output image using a smoothing and stretching method of an input image.

In general, a histogram shows the distribution of contrast values for pixels in an image. That is, the range and value of the distribution for the light and dark points in an image are expressed.

Histogram smoothing and stretching methods are used to improve the contrast of an image using such a histogram.

The histogram smoothing and stretching device according to the prior art will now be described in detail with reference to the accompanying drawings.

1 is a block diagram of a histogram smoothing device according to the prior art, FIGS. 2 to 5 are graphs showing a histogram by histogram smoothing according to the prior art, FIG. 6 is a block diagram of a histogram stretching device according to the prior art, and FIG. Is a graph showing the histogram by the histogram stretching method according to the prior art.

First, as shown in FIG. 1, the histogram equalization apparatus 100 according to the prior art includes a histogram generator 110 and a smoother 120.

Here, the histogram generator 110 generates a histogram indicating the number of pixels of each contrast of the input image. In this case, as shown in FIG. 2, one of the input images, such as A, B, C, and D, is divided into different areas of light or dark, which is called contrast.

In addition, the histogram is a graph showing the number of pixels belonging to each contrast based on the brightness of each contrast. As shown in FIG. 3, the histogram corresponds to the brightness of 32 A region, and represents 3/8 of the entire image. You can graph it like a histogram a. In the same way, histograms b, c and d can also be graphed.

As illustrated in FIG. 4, the smoothing unit 120 has a maximum brightness of each of the contrasts A, B, C, and D of the input image represented by the histograms a, b, c, and d. The histogram d corresponding to the contrast D having the maximum brightness of the input image is positioned at 255, and the remaining histograms a, b, and c are moved in accordance with the ratio of the histogram d, and then outputted. Will print

In this case, as shown in FIG. 5, when the histograms (a, b, c, d) of each of the shifted contrasts (A, B, C, and D) are accumulated and represented as a cumulative distribution diagram, 0 to 1 You can see that it has a slope. Since it has a slope of 1 and thus can be referred to as a uniform probability density, the output image output from the histogram smoothing apparatus 100 has a light and dark distribution of the entire zero area more uniformly than the input image.

In addition, as shown in FIG. 6, the histogram stretching device 200 according to the prior art includes a histogram generator 210 and a stretcher 220.

Here, the histogram generator 210 operates in the same manner as the histogram generator 110 of the histogram smoothing apparatus 100 described above.

As shown in FIG. 7, the stretching unit 220 moves the histogram a having the minimum brightness among the histograms a, b, c, and d generated by the histogram generator 210 to zero brightness and maximum brightness. Move the histogram d with to brightness 255.

Then, the histograms b and c are calculated according to Equation 1 below to move to each calculated position.

For example, the histogram b having the brightness value 64 is moved to the point of ((64-32) / (128-32)) * 255 = 85 according to Equation 1 above. At this time, the brightness value of the histogram d of the maximum brightness is 128, and the brightness value of the histogram a of the minimum brightness is 32.

In the same way, the histogram c having the brightness value 112 is moved to the point 213.

Therefore, when the input image is processed using the histogram smoothing apparatus 100 and the histogram stretching apparatus 200, the contrast values are uniformly distributed by spreading the contrast values concentrated in one place, so that the dark image is bright and bright. The image is darkened to maintain the appropriate brightness value.

However, when the input image is processed using the histogram smoothing apparatus 100, as shown in FIG. 5, the slope has 1, but the intervals e, f, g, and d of the histograms a, b, c, and d, respectively. And h maintains non-uniform intervals regardless of the sizes of the histograms a, b, c and d, and thus does not achieve an accurate uniform distribution. Therefore, the output image does not have the maximum contrast.

In addition, when the input image is processed using the histogram stretching apparatus 200, as shown in FIG. 7, the intervals i, j, and k of the histograms a, b, c, and d are constant regardless of their size. There is a problem that the output image does not have the maximum contrast because it does not achieve an accurate uniform distribution because the interval is not maintained.

The present invention has been made to solve the above problems, and an object of the present invention is to increase the contrast by generating an output image by a smoothing and stretching method in consideration of the size of the neighboring histogram and To provide a method.

Contrast enhancement apparatus using a histogram according to the present invention for achieving the above object, the histogram generator for generating a histogram indicating the number of pixels and brightness for each contrast of the input image; An expansion unit for expanding the histogram generated by the histogram generating unit to the entire section of the brightness region; A first calculator configured to sum up each neighboring histogram in the extended histogram and calculate a sum of the summed histograms; A second calculator for dividing each histogram by the total calculated by the first calculator to calculate an interval between neighboring histograms; And moving the histogram to a position calculated by the second calculator, thereby generating an output image.

In addition, in the contrast enhancement apparatus using the histogram according to the present invention, the extension unit moves the histogram having the maximum brightness value among the histograms generated by the histogram generator to the maximum brightness point of the entire section of the brightness region, The remaining histogram may be moved according to the moving ratio of the histogram having the maximum brightness value.

In addition, in the contrast enhancement apparatus using the histogram according to the present invention, the first calculating unit discards the histogram having the maximum brightness value after summing each neighboring histogram.

Contrast enhancement method using a histogram according to the present invention for achieving the above object comprises the steps of: a) generating a histogram indicating the number of pixels and brightness for each contrast of the input image; b) extending the histogram generated in step a) to the entire section of the brightness region; c) summing each histogram neighboring in the expanded histogram in step b) and calculating the sum of the summed histograms; d) dividing each histogram by the sum calculated in step c) to calculate an interval with a neighboring histogram; And e) moving each histogram to the position calculated in step d), thereby generating an output image.

In addition, in the contrast enhancement method using the histogram according to the present invention, the step b), the histogram having the maximum brightness value of the histogram generated in the step a) is moved to the maximum brightness point of the entire section of the brightness region, The remaining histogram may be moved according to the moving ratio of the histogram having the maximum brightness value.

In addition, in the contrast enhancement apparatus using the histogram according to the present invention, the step c) is to discard the histogram having the maximum brightness value after summing each histogram neighboring among the histograms expanded in the step b). It is done.

The above objects, features, and advantages will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, whereby those skilled in the art may easily implement the technical idea of the present invention. There will be.

In addition, in describing the present invention, when it is determined that the detailed description of the known technology related to the present invention may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted.

Then, a contrast enhancement apparatus using a histogram according to the present invention will be described in detail with reference to the accompanying drawings.

8 is a block diagram schematically illustrating a contrast enhancement apparatus using a histogram according to the present invention, and FIGS. 9 to 13 are graphs showing a histogram by the contrast enhancement apparatus using a histogram according to the present invention.

First, as shown in FIG. 8, the contrast enhancement apparatus 300 using the histogram according to the present invention includes a histogram generating unit 310, an expansion unit 320, a first calculating unit 330, and a second calculating unit ( 340 and an output image generator 350.

Here, the histogram generator 310 generates a histogram indicating the number of pixels and the brightness of each contrast of the input image. That is, as shown in FIG. 2, one input image is divided into different areas, such as A, B, C, and D, among the input images, as light or dark.

Each of the divided contrasts has a different number of pixels, and the histogram shows the number of pixels belonging to each contrast based on the brightness of each contrast.

The expansion unit 320 is connected to the histogram generating unit 310 and extends the histograms a, b, c and d shown in FIG. That is, the histogram d having the maximum brightness value is moved to the brightness 255 point in the same manner as the normal smoothing method, and the remaining histograms a, b, and c are moved in accordance with the moving ratio of the histogram d. As described above, the histograms a, b, c, and d are extended to the entire area based on the brightness.

The first operation unit 330 is connected to the expansion unit 320 and adds the histograms neighboring in the extended histograms a, b, c, and d, and calculates a sum of the summed histograms.

At this time, in the method of adding up the neighboring histogram, the histogram a is added up with the neighboring histogram b. The summed histogram a has a value of 3/8 + 1/8 = 1/2, the histogram b is summed with a neighboring histogram c to have a value of 1/2, and the histogram c also has a neighboring histogram d. This adds up to 1/2 the value.

Then, the histogram d having the maximum brightness value is discarded after the summation, so that histograms of the summed histograms a ', b' and c 'can be obtained as shown in FIG.

In addition, the first calculator 330 sums all pixel values representing the magnitudes of the histograms a ', b', and c ', which are added with the neighboring histogram, to obtain a total of these. At this time, the sum of the summed histogram a ', b' and c 'is 1/2 + 1/2 + 1/2 = 3/2.

The second calculator 340 is connected to the first calculator 320, and divides the summed histograms a ', b', and c 'into a sum calculated by the first calculator 330 and neighbors. Calculate the interval with the histogram.

In this case, the method of calculating the interval between neighboring histograms in the second calculating unit 340 divides the histogram a 'by a total of 3/2, where (1/2) / (3/2) = 1/3. The histograms b 'and c' are also computed in the same way, with values of 1/3 and 1/3 respectively. In this case, the obtained values represent intervals of neighboring histograms a, b, c, and d in FIG. 9 before being summed.

The output image generating unit 350 is connected to the expansion unit 320 and the second calculating unit 340, and the expansion unit 320 before being calculated by the first and second calculating units 330 and 340. Each histogram a, b, c, and d applied from is moved to a position calculated by the second calculator 340, thereby generating an output image.

In particular, as shown in FIG. 11, the output image generator 350 has a minimum brightness value and a maximum brightness value among the histograms a, b, c, and d in order to position the histogram at the calculated position. Place histograms a and d on the graph at the minimum brightness values 0 and 255, respectively.

Then, the output image generator 350 moves the histogram b to point 85 which is one third of the entire brightness range 255 so as to maintain a constant distance from the neighboring histogram a. In addition, the histogram c is moved to 170, 1/3 of the overall brightness range 255, so as to maintain a constant distance from the neighboring histogram b.

12, the histograms a, b, c, and d moved by the output image generator 350 affect the neighboring histograms. This is the part E marked with a dotted line.

Integrating all the areas along the portion E and representing the cumulative distribution may be represented as shown in FIG. 13, where the cumulative distribution has a value of 1 and may be referred to as a uniform probability density.

In addition, since the intervals of the histograms are determined according to the size of each histogram, that is, the number of pixels, an output image having the maximum contrast can be generated by forming an accurate uniform distribution.

Then, the contrast improvement method using the contrast improvement apparatus which consists of such a structure is demonstrated in detail.

14 is a flowchart schematically illustrating a contrast enhancement method using a histogram according to the present invention.

First, a histogram representing the number of pixels and the brightness of each contrast of the input image is generated (S401).

Then, the histogram generated in step S401 is extended to the entire section of the brightness region (S402). In this case, in step S402, the histogram having the maximum brightness value among the generated histograms is moved to the maximum brightness point of all sections of the brightness region, and the remaining histogram is moved according to the moving ratio of the histogram having the maximum brightness value. To expand.

In step S402, the neighboring histogram is expanded among the extended histograms (S403). In this case, in operation S402, the histogram having the maximum brightness value is discarded after summing the neighboring histograms.

The total sum of the histograms added in step S403 is calculated (S404), and each histogram is divided by the calculated sum to calculate an interval between neighboring histograms (S405).

Next, each histogram is moved to the position calculated in step S405, and an output image is generated through this (S406).

One preferred embodiment of the present invention described above is disclosed for the purpose of illustration, various substitutions, modifications and Modifications may be made and such substitutions, changes and the like should be regarded as belonging to the following claims.

As described above, the apparatus and method for improving a contrast according to the present invention has an effect of improving the contrast by generating an output image having an accurate uniform density by a smoothing and stretching method considering the size of a neighboring histogram.

Claims (6)

A histogram generator for generating a histogram indicating the number of pixels and the brightness of each contrast of the input image; An expansion unit for expanding the histogram generated by the histogram generating unit to the entire section of the brightness region; A first calculator configured to sum up each neighboring histogram in the extended histogram and calculate a sum of the summed histograms; A second calculator for dividing each histogram by the total calculated by the first calculator to calculate an interval between neighboring histograms; An output image generator for moving each histogram to a position calculated by the second calculator and generating an output image through the second histogram; Contrast enhancement device comprising a. The method of claim 1, The expansion unit, The histogram having the maximum brightness value among the histograms generated by the histogram generator is moved to the maximum brightness point of the entire section of the brightness region, and the remaining histogram is moved according to the moving ratio of the histogram having the maximum brightness value. Contrast enhancement device made with. The method of claim 1, The first operation unit, And a histogram having the maximum brightness value is discarded after summing each neighboring histogram. a) generating a histogram representing the number of pixels and the brightness for each contrast of the input image; b) extending the histogram generated in step a) to the entire section of the brightness region; c) summing each histogram neighboring in the expanded histogram in step b) and calculating the sum of the summed histograms; d) dividing each histogram by the sum calculated in step c) to calculate an interval with a neighboring histogram; And e) moving each histogram to the position calculated in step d), and thereby generating an output image; Contrast enhancement method comprising a. The method of claim 4, wherein In the step b), the histogram having the maximum brightness value of the histogram generated in step a) is moved to the maximum brightness point of all sections of the brightness region, and the remaining histogram is moved according to the moving ratio of the histogram having the maximum brightness value. Contrast improvement method characterized in that. The method of claim 4, wherein The step c), the sum of the neighboring histograms of the extended histogram in step b) discards the histogram having the maximum brightness value.

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