CN108305227A - A kind of method that the image low brightness area that contrast is constant highlights - Google Patents
A kind of method that the image low brightness area that contrast is constant highlights Download PDFInfo
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- CN108305227A CN108305227A CN201810064911.9A CN201810064911A CN108305227A CN 108305227 A CN108305227 A CN 108305227A CN 201810064911 A CN201810064911 A CN 201810064911A CN 108305227 A CN108305227 A CN 108305227A
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- 238000013507 mapping Methods 0.000 claims abstract description 17
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- 238000004364 calculation method Methods 0.000 claims description 4
- 238000012545 processing Methods 0.000 abstract description 2
- 238000004422 calculation algorithm Methods 0.000 description 6
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G06T5/00—Image enhancement or restoration
- G06T5/90—Dynamic range modification of images or parts thereof
- G06T5/92—Dynamic range modification of images or parts thereof based on global image properties
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G06T2207/00—Indexing scheme for image analysis or image enhancement
- G06T2207/20—Special algorithmic details
- G06T2207/20024—Filtering details
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G06T2207/00—Indexing scheme for image analysis or image enhancement
- G06T2207/20—Special algorithmic details
- G06T2207/20172—Image enhancement details
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Abstract
The present invention relates to image processing fields, and in particular to a kind of method that the image low brightness area that contrast is constant highlights.The present invention obtains the intensity map of image by calculating and filtering, gray scale stretching is carried out to image to construct nonlinear mapping function, the average brightness of low brightness area can be promoted under the premise of keeping image overall contrast ratio and constant high-brightness region total brightness.
Description
Technical field
The present invention relates to image processing fields, and in particular to a kind of image low brightness area that contrast is constant highlights
Method.
Background technology
The acquisition process of image there are various uncertain factors, easily lead to its quality decline or degenerate, such as part it is low it is bright,
Resolution ratio is low etc., this just needs to utilize image enhancement technique, improves its visual effect.Image enhancement analyzes image
Link is pre-processed, that is, the form more suitable for eye-observation and equipment analysis identification is converted images into, to protrude image detail
And contrast.
Directly enhance algorithm based on spatial domain, gradation of image can be handled, including Gamma correction methods, contrast are drawn
Stretch method, histogram equalization, Wavelet Transform etc..The processing method of frequency domain is based on the Fourier transformation for changing image, packet
Include multi-scale enhancement, small echo enhancing and Butterworth high-pass filtering etc..
More advanced image enhancement will then use the visual characteristic of human eye, such as establish in human color's shape constancy phenomenon
Retinex theories formalization, and single scale Retinex algorithm (the Single Scale that obtain on this basis
Retinex, SSR), multi-Scale Retinex Algorithm (Multi-Scale Retinex, MSR) and multiple dimensioned color recieving
Retinex algorithm (Multi-Scale Retinex with ColorRestoration, MSRCR), these methods can enhance figure
Image contrast, but computation complexity is high, and color of image is easily distorted.
In addition the algorithm for image enhancement that a kind of frequency domain of current research is combined with spatial domain introduces Butterworth high-pass filtering
The correlation properties of (Butterworth High Pass Filter, BHPF) carry out image procossing.Set a Nonlinear Mapping
Model adjusts image integral brightness level by logarithmic transformation method, image-region range is calculated by bilateral filtering later
Average brightness, and local contrast enhancing is carried out, image color information is finally restored using simple linear method.But the party
Method changes the contrast of image, and can not enhance local low brightness area.
Invention content
The object of the present invention is to provide a kind of methods that the image low brightness area that contrast is constant highlights, to solve
The problem of certainly prior art cannot highlight under the premise of keeping contrast to local low brightness area.
To achieve the above object, it is bright to aspects of which provide a kind of image low brightness area that contrast is constant enhancing
The method of degree, including method scheme one, method scheme one include the following steps：
The luminance picture of original image is calculated；
Low-pass filtering treatment is carried out to the luminance picture and obtains intensity map；
Nonlinear mapping function is constructed according to the luminance picture and the intensity map；
Gray scale stretching is carried out to the original image according to the nonlinear mapping function, obtains low-light level enhancing image.
Method scheme two, on the basis of method scheme one, the formula of the nonlinear mapping function is：
Wherein, Yr′/g/b(x, y) is gray value of the pixel after the gray scale stretching on the original image；Yr/g/b
(x, y) is the gray value of pixel on the original image, and Medium (x, y) is pixel Yr/g/b(x, y) is in the brightness point
Corresponding gray value, Y on BututminIt is the minimum gradation value of the luminance picture, YavgIt is the average gray of the luminance picture
Value.
Method scheme three, four, respectively on the basis of method scheme one, two, the low-pass filtering is mean filter, Gauss
Filtering or medium filtering.
Method scheme five, six, respectively on the basis of method scheme three, four, the gray value of the gray level image calculates public affairs
Formula is：
Y (x, y)=max { r (x, y), g (x, y), b (x, y) }
Wherein, r (x, y), g (x, y), b (x, y) are the RGB triple channel pixel values of original image.
The beneficial effects of the invention are as follows：The intensity map of image is obtained by calculating and filtering, is then constructed non-linear
Mapping function carries out gray scale stretching to image, can be before keeping image overall contrast ratio and high-brightness region total brightness constant
It puts, judge the position of low brightness area and promotes the average brightness of low brightness area.
Description of the drawings
Fig. 1 is the flow chart of the method for the invention；
Fig. 2 is the medium filtering Prototype drawing in the embodiment of the present invention.
Specific implementation mode
The present invention will be further described in detail below in conjunction with the accompanying drawings.
In order to solve the problems, such as brightness enhancing of local low brightness area under the premise of keeping contrast, the present invention proposes a kind of
The method that the constant image low brightness area of contrast highlights, is stretched through nonlinear function, constant in picture contrast
Under the premise of, low brightness area local luminance is promoted, while keeping high-brightness region unaffected.It is given below one specifically
Embodiment.
It is the flow chart of the present embodiment method as shown in Figure 1, including：
Input multichannel image；
Brightness calculation is carried out to input picture and obtains luminance picture；
The low-pass filtering of large scale, the intensity map of drawing image are carried out to luminance picture；
According to luminance picture and intensity map, nonlinear mapping function is constructed, ash is then carried out point by point to input picture
Degree stretches, and obtains the enhanced image of low brightness area.
In the above-mentioned methods, the computational methods of luminance picture calculate each of gray level image including but not limited to multichannel image
Kind common method.The computational methods of low-pass filtering are including but not limited to mean filter, gaussian filtering, medium filtering, this reality simultaneously
It applies example and uses medium filtering.
Average brightness is constant after the nonlinear mapping function of construction has holding high luminance area domain mapping, and low brightness area is reflected
Penetrate the increased characteristic of rear average brightness, and the characteristic that full figure contrast remains unchanged after mapping.
The multichannel image of input is transformed into the luminance picture process of characterization image each point luminance information by brightness calculation.This
Embodiment assumes that the RGB triple channel pixel values of input picture I (x, y) are respectively r (x, y), g (x, y) and b (x, y), luminance picture
The formula of Y (x, y) calculates：
Y (x, y)=max { r (x, y), g (x, y), b (x, y) }
The present embodiment uses 15 × 15 medium filtering template, and the scale of Filtering Template is related to the scale of image, such as Fig. 2
It is shown, it does convolution algorithm with luminance picture and obtains the intensity map of image.
Construct nonlinear mapping function, using image intensity map as guiding, to each channel of input picture by
Point carries out gray scale stretching, under the premise of realizing that holding contrast is constant, promotes the average brightness of low brightness area range
Effect.By taking input picture is RGB triple channels as an example, the building method of nonlinear mapping function is the present embodiment：Assuming that input figure
As RGB triple channel gray values are Yr/g/b, the triple channel gray value after gray scale stretching is Yr′/g/b, gray scale stretching use it is non-thread
Property mapping function is：
Wherein, Yr′/g/b(x, y) is gray value of the pixel after gray scale stretching on original image；Yr/g/b(x, y) is
The gray value of pixel on original image, Medium (x, y) are pixel Yr/g/bGray value on intensity map, YminIt is
The minimum gradation value of luminance picture, YavgIt is the average gray value of luminance picture.
The image of the low brightness area enhancing finally obtained, using original input picture luminance mean value as threshold value, in high brightness
Region keeps average brightness constant, and low brightness area brightness enhancing keeps contrast constant, and solves two regions well
Between overscale problems.
Specific implementation mode of the present invention is presented above, the Luminance Distribution of image is obtained by calculating and filtering
Then figure constructs nonlinear mapping function and carries out gray scale stretching to image, so as to keep image overall contrast ratio and height
Under the premise of luminance area total brightness is constant, the brightness in enhancing low-light level area.
But the present invention is not limited to described embodiment, and brightness calculation is carried out for example, by using other computational methods,
Or be filtered using other filtering modes, the technical solution formed in this way is to be finely adjusted to be formed to above-described embodiment
, this technical solution is still fallen in protection scope of the present invention.
Claims (4)
1. a kind of method that the image low brightness area that contrast is constant highlights, which is characterized in that include the following steps：
The luminance picture of original image is calculated；
Low-pass filtering treatment is carried out to the luminance picture and obtains intensity map；
Nonlinear mapping function is constructed according to the luminance picture and the intensity map；
Gray scale stretching is carried out to the original image according to the nonlinear mapping function, obtains low-light level enhancing image.
2. the method that a kind of constant image low brightness area of contrast according to claim 1 highlights, feature
It is：The formula of the nonlinear mapping function is：
Wherein, Yr′/g/b(x, y) is gray value of the pixel after the gray scale stretching on the original image；Yr/g/b(x,y)
It is the gray value of pixel on the original image, Medium (x, y) is pixel Yr/g/b(x, y) is on the intensity map
Corresponding gray value, YminIt is the minimum gradation value of the luminance picture, YavgIt is the average gray value of the luminance picture.
3. the method that a kind of constant image low brightness area of contrast according to claim 1 or 2 highlights, special
Sign is：The low-pass filtering is mean filter, gaussian filtering or medium filtering.
4. the method that a kind of constant image low brightness area of contrast according to claim 3 highlights, feature
It is：The gray value calculation formula of the luminance picture is：
Y (x, y)=max { r (x, y), g (x, y), b (x, y) }
Wherein, r (x, y), g (x, y), b (x, y) are the RGB triple channel pixel values of the original image.
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Cited By (1)
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| CN109447912A (en) * | 2018-10-18 | 2019-03-08 | 广东欧谱曼迪科技有限公司 | A kind of fluorescent image of fluorescence navigation endoscopic system adaptively enhances and noise-reduction method |
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