CN111161194B - Image processing method - Google Patents
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- CN111161194B CN111161194B CN201911424350.XA CN201911424350A CN111161194B CN 111161194 B CN111161194 B CN 111161194B CN 201911424350 A CN201911424350 A CN 201911424350A CN 111161194 B CN111161194 B CN 111161194B
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- G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
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- G06T7/90—Determination of colour characteristics
Abstract
The application provides an image processing method, which is characterized in that the problems of tone deviation and detail loss are improved by performing contrast enhancement image processing on an original image in the same color space. Further, the self-adaptive saturation compensation image processing is carried out on the contrast output pixels according to the original image brightness value and the contrast output brightness value, so that the saturation attenuated by the contrast enhanced image processing is compensated, and the problem of saturation reduction is solved.
Description
Technical Field
The present application relates to the field of image processing technologies, and in particular, to an image processing method for improving the problems of hue shift, detail loss, and saturation reduction.
Background
With the progress of technology, the requirements of color image quality are higher and higher, and in order to improve color image quality, image processing for improving contrast and enhancing saturation is generally performed, so that the color image seen by human eyes can be closer to a real scene, and therefore, the color adjustment technology is becoming more and more important.
In the conventional image processing method, the color image in the RGB color space is input and converted into the Hue-Saturation-Intensity (HSI) color space to perform image processing for improving the contrast, and then the histogram is counted, clipped and equalized (Histogram Equalization) on the luminance components, and then the Hue component, the Saturation component and the adjusted luminance component are converted back into the RGB color space together, and finally the image is output, so as to realize the processing for improving the contrast of the color image. However, according to the characteristics of the HIS color space, when the luminance component is raised to a certain extent, some values exceed the boundary of the color gamut, so that the values outside the color gamut are usually cut and discarded, which results in the offset of the hue and the loss of details, and even causes a serious problem of saturation reduction. Therefore, there is a need for an image processing method to improve the problems of color shift, loss of detail, and saturation reduction in the prior art.
Disclosure of Invention
The present application aims to provide an image processing method for improving problems of hue shift, loss of detail, and saturation reduction.
To achieve the above object, an aspect of the present application provides an image processing method including the steps of:
inputting an original image with original image pixels and original image brightness values, and carrying out contrast-enhanced image processing on the original image pixels to obtain contrast output brightness values;
according to a preset brightness mapping function provided by a brightness mapping mechanism, mapping the contrast output brightness value into a tone plane to obtain a contrast output pixel;
providing a saturation compensation value for the contrast output pixel according to a saturation compensation mechanism so as to perform saturation compensated image processing;
the contrast output pixels are stretched and translated according to a saturation mapping mechanism, so that the contrast output pixels after saturation compensation, namely saturation output pixels, are obtained; and
and outputting the saturation output pixel.
Further, the contrast-enhanced image processing is performed on the original image by a histogram equalization method.
Further, the contrast-enhanced image processing is performed on the original image by a method of attenuating saturation to some extent.
Further, the luminance mapping function is:
wherein w is OL Outputting pixels, w, for said contrast i For the original image pixels, w t Is a demarcation pixel point in the hue plane, L OL Outputting a brightness value for the contrast ratio L i For the original image brightness value, L t A, alpha, which is the demarcation brightness value of the demarcation pixel point a 、α b2 、α c2 And alpha d Is the expansion and contraction amount.
Further, the saturation compensation value is:
wherein S is comp For the saturation compensation value, L OL Outputting a brightness value for the contrast ratio L i For the original image brightness value, L t Is the demarcation brightness value of the demarcation pixel point in the hue plane.
Further, the gamma value ranges from 0 to 1.
Further, the saturation compensation value is:
when->
Wherein S is comp For the saturation compensation value, L OL Outputting a brightness value for the contrast ratio L i For the original image brightness value, L t Boundary brightness value S for boundary pixel point in tone plane OL Output saturation for contrast, S i Is the original image saturation.
Further, the gamma value ranges from 0 to 1.
Further, the saturation output pixel is obtained by the principle that the saturation of the contrast output pixel, the saturation of the saturation output pixel and the pixel brightness values before and after the image processing of the saturation compensation on the contrast output pixel are unchanged.
Further, the tone of the original image pixel, the contrast output pixel, and the saturation output pixel is unchanged.
The application improves the problems of color tone deviation and detail loss existing in the prior art by firstly carrying out contrast enhancement image processing on the original image in the same color space. Further, the self-adaptive saturation compensation image processing is performed according to the original image pixel brightness value and the contrast output pixel brightness value, so that the saturation attenuated by the contrast enhanced image processing is compensated, and the problem of saturation reduction is solved. It can be seen that the present application has substantial utility and significant advantages.
Drawings
Fig. 1 is a schematic flow chart of an image processing method provided by the application.
Fig. 2 is a schematic diagram of steps of an image processing method according to the present application.
Fig. 3A-3D are schematic diagrams illustrating a brightness mapping mechanism according to the present application.
Fig. 4A-4F are schematic diagrams of a saturation compensation mechanism provided by the present application.
Detailed Description
In order to make the objects, technical solutions and effects of the present application more clear and clear, the present application will be described in further detail below with reference to the accompanying drawings. It should be understood that the particular embodiments described herein are illustrative only and that the terms "embodiment" or "exemplary" as used in the specification of the present application are intended to be used as examples, illustrations or exemplifications, and are not intended to limit the application.
Referring to fig. 1 and fig. 2 simultaneously, fig. 1 is a flow chart of an image processing method provided by the present application, and fig. 2 is a step chart of an image processing method provided by the present application, the method includes the following steps:
step S10, inputting an original image with original image pixels and original image brightness values, and carrying out contrast enhancement image processing on the original image pixels to obtain contrast output brightness values.
In a hue plane in an RGB color space (as in the triangles of fig. 3A-3D and fig. 4A-4F), one vertex coordinate (0, 0) is the darkest point (black point) of the hue plane, one vertex coordinate (1, 1) is the brightest point (white point) of the hue plane, the other vertex is a color point, wherein the line connecting the coordinate (0, 0) and the coordinate (1, 1) is the luminance axis, the color point has a demarcation luminance value L t (i.e. the color point corresponds to a luminance value L on the luminance axis t ) And when the color point is red, green, and blueThe triangles are then a red hue plane with a red component, a green hue plane with a green component, and a blue hue plane with a blue component, respectively. The present application is described in detail below with respect to the RGB color space as a preferred embodiment.
In this step, the original image is in RGB color space with a red component R i Green component G i And a blue component B i Original image pixel w of (1) i (R i ,G i ,B i ) Which has an original image brightness value L i (i.e. the original image pixel w i A luminance value L corresponding to the luminance axis i ) And the original image brightness value L i Can be the original image pixel w i Sum of color components of (1), i.e. L i ＝R i +G i +B i . The application first uses the original image pixel w in RGB color space i Image processing with contrast enhancement, that is to say for the original image pixels w i Processing the brightness level in RGB color space to obtain contrast output brightness value L OL (i.e. the brightness value on the brightness axis is L OL )。
In an embodiment, the original image may be subjected to contrast enhancement by histogram equalization, or may be subjected to saturation attenuation, which is not limited thereto.
Step S20, according to the preset brightness mapping function provided by the brightness mapping mechanism, the contrast output brightness value is mapped in the tone plane to obtain the contrast output pixel.
For convenience of description, the description may be directly given by a code, for example, may be directly given by "w i "representing" an original image pixel w i ”。
At the original image pixel w i After image processing for contrast enhancement in RGB color space, the present application outputs the contrast to brightness value L by a preset brightness mapping function provided by brightness mapping mechanism OL Mapping in the tone plane to obtain a contrast output pixel w OL At this time, the contrast ratio outputs the pixel w OL And the original image pixel w i Having w OL ＝α i ×w i +β i The relation of the original image pixel w i Through expansion alpha i And translate beta i Can then be obtained with a red component R OL Green component G OL And a blue component B OL Contrast output pixel w of (2) OL (R OL ,G OL ,B OL ). In addition, since the processing is to simultaneously pixel w of the original image in the RGB color space i The color components of the image processing device are stretched and translated, so that the principle that the color tone is unchanged before and after image processing can be maintained.
Fig. 3A-3D are schematic diagrams of a brightness mapping mechanism according to the present application. To obtain contrast output pixel w OL The application is based on the preset brightness mapping function and passes L i 、L OL And L t The positional relationship of the three hue planes in the RGB color space specifically suggests 4 contrast output pixels w OL The brightness mapping mechanism proposed by the present application can be understood as the original image pixel w i And contrast output pixel w OL Projection on luminance axis calculated as luminance value):
(1) When L i ≤L t And L is OL ≤L t (as shown in fig. 3A): l (L) OL Contrast output pixel w mapped on hue plane OL In terms of coordinates (0, 0) and original image pixel w i In the direction of the extension line of the contrast output pixel w OL Is the expansion and contraction quantity alpha a The coordinates (0, 0) of the multiple are compared with the original image pixel w i Of (a), that is to say alpha a ＝L OL /L i Thus contrast output pixel w OL ＝α a ×w i 。
(2) When L i ≤L t And L is OL ≥L t (as shown in fig. 3B): l (L) OL Contrast output pixel w mapped on hue plane OL To the original image pixel w along the coordinates (0, 0) i In the direction of the extension line of the connection line of (a)Along and intersecting a vertical line from the color point to the luminance axis at a demarcation pixel point w t Then from the demarcation pixel point w t Extending in the direction of the coordinates (1, 1) to the contrast output pixel w OL At this time, the boundary pixel point w t Is the expansion and contraction quantity alpha b1 The multiplied coordinates (0, 0) and the original image pixels w i Of (a), that is to say alpha b1 ＝L t /L i And w is t ＝α b1 ×w i And the contrast ratio output pixel w OL The amount of warping α is subtracted for all (i.e. normalized RGB color space, value = 1) b2 Doubling the original image pixel w i Connection to coordinates (1, 1), that is to say alpha b2 ＝(1-L OL )/(1-L i ) Thus contrast output pixel w OL ＝1-α b2 × (1-w i )。
(3) When L i >L t And L is OL <L t (as shown in FIG. 3C): L OL Contrast output pixel w mapped on hue plane OL For the original image pixel w along the coordinates (1, 1) i Extending in the direction of the extension line of the color point to the brightness axis and intersecting the vertical line of the color point to the brightness axis at a demarcation pixel point w t Then from the demarcation pixel point w t Extending in the direction of the coordinates (0, 0) to the contrast output pixel w OL At this time, the boundary pixel point w t The amount of warping α is subtracted for all (i.e. normalized RGB color space, value = 1) c1 Doubling the original image pixel w i Connection to coordinates (1, 1), that is to say alpha c1 ＝(1-L t )/(1-L i ) And w is t ＝ 1-α c1 ×(1-w i ) Thus passing through the expansion and contraction amount alpha c2 Is a contrast output pixel w of (1) OL ＝α c2 ×w t 。
(4) When L i >L t And L is OL >L t (as shown in FIG. 3D): L OL Contrast output pixel w mapped on hue plane OL In terms of coordinates (1, 1) and original image pixel w i In the direction of the extension of the line of (a) in which the contrast is outputPixel w OL The amount of warping α is subtracted for all (i.e. normalized RGB color space, value = 1) d The coordinates (1, 1) of the magnification and the original image pixel w i Of (a), that is to say alpha d ＝ (1-L OL )/(1-L i ) Thus contrast output pixel w OL ＝1-α d ×(1-w i )。
And step S30, providing a saturation compensation value for the contrast output pixel according to a saturation compensation mechanism so as to perform saturation compensated image processing.
Although the application can avoid the problems of color shift and detail loss caused by converting the HIS color space into the RGB color space after the contrast enhancement in the prior art by carrying out the image processing of the contrast enhancement in the RGB color space, the application is similar to the original image pixel w i The phase ratio produces a decay in saturation. Specifically, the line of coordinates (0, 0) and the color point in the hue plane of the RGB color space has the highest saturation (saturation value=1), while the line of coordinates (0, 0) and coordinates (1, 1) has the lowest saturation (saturation value=0), so that the pixel w is outputted if it is contrast OL Falls on coordinates (0, 0) and original image pixel w i Or on the line of coordinates (1, 1) and the original image pixel w i On the line of (2), a contrast ratio is output to the pixel w OL Is equal to the saturation of the original image pixel w i No attenuation is generated, whereas saturation attenuation is generated. The present application thus further provides saturation-compensated image processing, the saturation compensation mechanism being to output pixels w for said contrast OL A saturation compensation value is provided for saturation compensation. Referring to fig. 4A-4F, fig. 4A-4F are schematic diagrams of a saturation compensation mechanism according to the present application, wherein the saturation compensation mechanism performs certain compensation according to different saturation attenuation degrees, and is according to L i 、L OL And L t The positional relationship of the hue planes of the three in the RGB color space specifically proposes the case of 6 saturation compensation values:
(1) When L i ≥L t And L is t ≥L i (as shown in fig. 4A): saturation compensation value S comp And contrast output brightness value L OL Boundary brightness value L t Is a difference function f (L) OL -L t ) In direct proportion to the saturation compensation valueOr with contrast output saturation S OL Original image pixel saturation S i Is a difference function f (S OL -S i ) In direct proportion to, i.e
(2) When L OL >L i >L t (as shown in fig. 4B): saturation compensation value S comp And contrast output brightness value L OL Original image brightness value L i Is a difference function f (L) OL -L i ) In direct proportion to the saturation compensation valueOr with contrast output saturation S OL Original image saturation S i Is a difference function f (S OL -S i ) In direct proportion to, i.e
(3) When L t >L OL >L i (as shown in fig. 4C): output pixel w due to contrast OL Falls on coordinates (0, 0) and original image pixel w i Therefore, no saturation attenuation phenomenon, that is, saturation compensation value S, occurs comp Zero.
(4) When L i >L t >L OL (as shown in fig. 4D): saturation compensation value S comp And boundary brightness value L t Contrast output luminance value L OL Is a difference function f (L) t -L OL ) In direct proportion to the saturation compensation valueOr with contrast output saturation S OL Original image saturation S i Is a difference function f (S OL -S i ) In direct proportion to, i.e
(5) When L t >L i >L OL (as shown in fig. 4E): saturation compensation value S comp And the original image brightness value L i Contrast output pixel brightness value L OL Is a difference function f (L) i -L OL ) In direct proportion to the saturation compensation valueOr with contrast output saturation S OL Original image saturation S i Is a difference function f (S OL -S i ) In direct proportion to, i.e
(6) When L i >L OL >L t (as shown in fig. 4F): output pixel w due to contrast OL Falling to coordinates
(1, 1) and original image pixel w i Therefore, no saturation attenuation phenomenon, that is, saturation compensation value S, occurs comp Zero.
In one embodiment, the saturation of each pixel corresponds to the following relationship:
according to the saturation compensation mechanism, the contrast output pixels w with different contrast enhancement amplitudes can be realized OL Adaptive saturation compensation is performed, whichThe gamma value in (a) ranges from 0 to 1, alternatively 0.2, the greater the gamma value the less the intensity of saturation compensation and vice versa.
And S40, stretching and translating the contrast output pixel according to a saturation mapping mechanism to obtain the contrast output pixel after saturation compensation, namely a saturation output pixel.
Contrast output pixel w after saturation compensation OL Output luminance value L for having saturation OS (i.e. corresponding to a luminance value L on the luminance axis) OS ) Saturation output pixel w of (2) OS At this time, the saturation output pixel w OS And contrast output pixel w OL Having w OS ＝α L ×w OL +β L The relation of the contrast output pixel w OL Telescoping alpha in RGB color space L And translate beta L To obtain a red component R OS Green component G OS And a blue component B OS Saturation output pixel w of (2) OS (R OS ,G OS ,B OS ) Image processing due to saturation compensation is to output pixels w for contrast in the RGB color space simultaneously OL The contrast output image is stretched and translated so that the hue remains unchanged before and after saturation-compensated image processing.
In one embodiment, the method comprises the step of OL And S is equal to OS And the principle that the pixel brightness value is unchanged before and after saturation compensation (i.e. L OS ＝L OL ) And then get alpha L And beta L To obtain saturation output pixel w OS Wherein L is OL ＝R OL +G OL +B OL ，L OS ＝R OS +G OS +B OS 。
And S50, outputting the saturation output pixel.
In summary, the present application provides an image processing method, which is to perform contrast-enhanced image processing on an original image in the same color space, so as to solve the problems of color tone shift and detail loss in the prior art. Further, the self-adaptive saturation compensation image processing is carried out on the contrast output pixels according to the original image brightness value and the contrast output brightness value, so that the saturation attenuated by the contrast enhanced image processing is compensated, and the problem of saturation reduction is solved. It can be seen that the present application has substantial utility and significant advantages.
Although the present application has been described with reference to the preferred embodiments, it should be understood that the present application is not limited to the preferred embodiments, and that various changes and modifications can be made by one skilled in the art without departing from the scope of the application as defined in the appended claims.
Claims (8)
1. An image processing method, characterized by comprising the steps of:
inputting an original image with original image pixels and original image brightness values, and carrying out contrast-enhanced image processing on the original image pixels to obtain contrast output brightness values;
according to a preset brightness mapping function provided by a brightness mapping mechanism, mapping the contrast output brightness value into a tone plane to obtain a contrast output pixel;
providing a saturation compensation value for the contrast output pixel according to a saturation compensation mechanism to perform saturation compensated image processing, wherein the saturation compensation value is:
wherein S is comp For the saturation compensation value, L OL Outputting a brightness value for the contrast ratio L i For the original image brightness value, L t A gamma value in a range of 0 to 1, which is a demarcation brightness value of demarcation pixel points in the tone plane;
the contrast output pixels are stretched and translated according to a saturation mapping mechanism, so that the contrast output pixels after saturation compensation, namely saturation output pixels, are obtained; and
and outputting the saturation output pixel.
2. The image processing method according to claim 1, characterized in that: and carrying out the contrast enhanced image processing on the original image by a histogram equalization method.
3. The image processing method according to claim 1, characterized in that: and carrying out the contrast-enhanced image processing on the original image by utilizing a method with a certain attenuation on the saturation.
4. The image processing method according to claim 1, wherein the luminance mapping function is:
wherein w is OL Outputting pixels, w, for said contrast i For the original image pixels, w t Is a demarcation pixel point in the hue plane, L OL Outputting a brightness value for the contrast ratio L i For the original image brightness value, L t A, alpha, which is the demarcation brightness value of the demarcation pixel point a 、α b2 、α c2 And alpha d Is the expansion and contraction amount.
5. The image processing method according to claim 1, wherein the saturation compensation value is:
wherein S is comp For the saturation compensation value, L OL Outputting a brightness value for the contrast ratio L i For the original image brightness value, L t For demarcations in the hue planeBoundary brightness value of pixel point S OL Output saturation for contrast, S i Is the original image saturation.
6. The image processing method according to claim 5, characterized in that: the gamma value ranges from 0 to 1.
7. The image processing method according to claim 1, characterized in that: and obtaining the saturation output pixel according to the saturation of the contrast output pixel, the saturation of the saturation output pixel and the principle that the brightness values of pixels before and after the image processing for carrying out the saturation compensation on the contrast output pixel are unchanged.
8. The image processing method according to claim 1, characterized in that: the tone of the original image pixel, the contrast output pixel, and the saturation output pixel is unchanged.
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| CN108711142A (en) * | 2018-05-22 | 2018-10-26 | 深圳市华星光电技术有限公司 | Image processing method and image processing apparatus |
| CN109146811A (en) * | 2018-08-14 | 2019-01-04 | 长沙全度影像科技有限公司 | A kind of Adaptive contrast enhancement method of color image |
| CN110175969A (en) * | 2019-05-29 | 2019-08-27 | 深圳市华星光电技术有限公司 | Image processing method and image processing apparatus |
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Patent Citations (4)
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| EP1017241A2 (en) * | 1998-12-31 | 2000-07-05 | Eastman Kodak Company | A method for compensating image color when adjusting the contrast of a digital color image |
| CN108711142A (en) * | 2018-05-22 | 2018-10-26 | 深圳市华星光电技术有限公司 | Image processing method and image processing apparatus |
| CN109146811A (en) * | 2018-08-14 | 2019-01-04 | 长沙全度影像科技有限公司 | A kind of Adaptive contrast enhancement method of color image |
| CN110175969A (en) * | 2019-05-29 | 2019-08-27 | 深圳市华星光电技术有限公司 | Image processing method and image processing apparatus |
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