imlocalbrighten

Brighten low-light image

Description

example

B = imlocalbrighten(A) brightens low-light areas in A, which is an RGB or grayscale image. Returns B, the locally brightened image, which is the same size and class as A.

B = imlocalbrighten(A,amount) brightens low-light areas in A, where amount specifies how much to brighten the dark areas of the image. Specify amount as a scalar in the range [0,1].

[B,D] = imlocalbrighten(___) returns the optional argument D, which is a matrix containing estimates of how dark each pixel is in the input image.

[___] = imlocalbrighten(___,'AlphaBlend',TF) brightens low-light areas in A, where 'AlphaBlend' specifies whether you want to preserve content of the input image in the output image. Specify TF as true or false (default). When true, imlocalbrighten alpha blends the input image with the enhanced image to preserve brighter areas of the input image. imlocalbrighten uses the estimate of darkness matrix, D, to preserve content of the input image proportional to the amount of light in each pixel. The parameter name can be abbreviated, and case does not matter.

Examples

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Brighten a low-light image using default parameters. View the original image and the lightened version of the image.

A = imread('lowlight_2.jpg');
B = imlocalbrighten(A);
figure, imshowpair(A,B,'montage')

Brighten the low-light image again, this time specifying the amount of lightening to apply to the image. View the original image and this lightened version of the image.

A = imread('lowlight_2.jpg');
B2 = imlocalbrighten(A,0.8);
figure, imshowpair(A,B2,'montage')

Use the AlphaBlend option to preserve content from the original image in the lightened image. This time, view the lightened output image from the first example with the alpha blended output image. Compare the detail shown in the wall above arched entryway near the center of the image in the alpha-blended version with the original lightened image.

A = imread('lowlight_2.jpg');
Bblend = imlocalbrighten(A,'AlphaBlend',true);
figure, imshowpair(B,Bblend,'montage')

Get the estimated darkness-per-pixel matrix return value. View the original image and the darkness estimate matrix.

A = imread('lowlight_2.jpg');
[~,D] = imlocalbrighten(A);
figure, imshowpair(A,D,'montage')

Input Arguments

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Image to be brightened, specified as a real, nonsparse, grayscale image (M-by-N) or RGB image (M-by-N-by-3).

Data Types: single | double | uint8 | uint16

How much to brighten the image, specified as a numeric scalar in the range [0 1]. When the value is 1 (the default), imlocalbrighten brightens the low-light areas of A as much as possible. When the value is 0, imlocalbrighten returns the input image unmodified.

Example: 0.2

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64

Output Arguments

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Brightened image, returned as a grayscale or an RGB image, the same size and class as the input image A.

Estimate of darkness of each pixel in the input image, returned as a numeric matrix. D is the same size as the first two dimensions of the input image and is of class double

References

[1] Dong, X., G. Wang, Y. Pang, W. Li, J. Wen, W. Meng, and Y. Lu. "Fast efficient algorithm for enhancement of low lighting video." Proceedings of IEEE® International Conference on Multimedia and Expo (ICME). 2011, pp. 1–6.

[2] He, Kaiming. "Single Image Haze Removal Using Dark Channel Prior." Thesis, The Chinese University of Hong Kong, 2011.

[3] Dubok Park; Hyungjo Park; David K. Han; Hanseok Ko "Single Image Dehazing with Image Entropy and Information Fidelity." ICIP, 2014.

Introduced in R2019b