How to adjust the intensity of grayscale image?

Question

ali brk 2022-1-1

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https://ww2.mathworks.cn/matlabcentral/answers/1620465-how-to-adjust-the-intensity-of-grayscale-image

评论： Image Analyst 2022-1-1

I create a 200x200 image then convert it to grayscale, how can i adjust its intensity between 0-255?

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Answer 1

Simon Chan 2022-1-1

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https://ww2.mathworks.cn/matlabcentral/answers/1620465-how-to-adjust-the-intensity-of-grayscale-image#answer_866110

Use function imcontrast

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Answer 2

Image Analyst 2022-1-1

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https://ww2.mathworks.cn/matlabcentral/answers/1620465-how-to-adjust-the-intensity-of-grayscale-image#answer_866155

在 MATLAB Online 中打开

There are lots of ways.

grayImage = imadjust(grayImage);
grayImage = rescale(grayImage, 0, 255);
grayImage = 255 * mat2gray(grayImage);

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ali brk 2022-1-1

i get totally black image in all combination with the following code:

Image = zeros(200,200,3)

Image_1 = rgb2gray(Image)

grayImage = imadjust(Image_1)

grayImage = rescale(grayImage,0,255)

grayImage = 255*mat2gray(grayImage)

Image Analyst 2022-1-1

在 MATLAB Online 中打开

They are not totally black. Did you look at them in the workspace? They will have non-zero values. Try displaying with [] as the second argument to imshow:

imshow(grayImage, []);

Of course with the sample code you gave, where you defined Image as a totally black image, you will get a totally black image even after it's contrast stretched. You have to use an image that actually has some structure to it and is not all black.

Don't use Image as the name of a variable since there is a built-in function image().

grayImage = imread('pout.tif');

subplot(1, 2, 1);

imshow(grayImage);

if ndims(grayImage) == 3

grayImage = rgb2gray(grayImage);

end

grayImage = imadjust(grayImage);

subplot(1, 2, 2);

imshow(grayImage, []);

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Answer 3

yanqi liu 2022-1-1

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https://ww2.mathworks.cn/matlabcentral/answers/1620465-how-to-adjust-the-intensity-of-grayscale-image#answer_866185

yes，sir，may be use

im = im2uint8(mat2gray(im));

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ali brk 2022-1-1

can you give more info?

yanqi liu 2022-1-1

在 MATLAB Online 中打开

yes，sir，may be use

%create a 200x200 image then convert it to grayscale,
%how can i adjust its intensity between 0-255?
% create a 200x200 image
im = rand(200,200,3);
% then convert it to grayscale
im = rgb2gray(im);
im(1:10,1:10)
ans = 10×10
    0.1511    0.6153    0.2279    0.2951    0.8098    0.3878    0.5535    0.4655    0.4006    0.3543
    0.3550    0.3707    0.3934    0.4972    0.5180    0.6047    0.4820    0.6322    0.3626    0.5538
    0.3975    0.5218    0.5015    0.2773    0.8051    0.7308    0.6066    0.6486    0.6455    0.1662
    0.2567    0.5993    0.5951    0.8354    0.3259    0.0769    0.1316    0.7617    0.7265    0.0289
    0.6379    0.5649    0.6424    0.3031    0.4472    0.8407    0.7261    0.4992    0.6738    0.4763
    0.5342    0.4933    0.6417    0.6855    0.5028    0.4122    0.3783    0.6598    0.5657    0.5953
    0.2551    0.4213    0.5610    0.4059    0.4440    0.5908    0.6452    0.5935    0.2587    0.3949
    0.8427    0.4115    0.6005    0.8031    0.6722    0.7559    0.5617    0.4079    0.7655    0.4716
    0.6689    0.5936    0.3186    0.6318    0.2224    0.3110    0.4287    0.5690    0.4872    0.4361
    0.3908    0.4320    0.3599    0.2860    0.5236    0.3848    0.7476    0.3502    0.2442    0.3136
% adjust its intensity between 0-255
im = im2uint8(mat2gray(im));
im(1:10,1:10)
ans = 10×10
    37   158    57    74   209    98   142   119   102    90
    90    94   100   127   132   155   123   162    92   142
   101   133   128    70   207   188   155   166   166    41
    64   154   152   215    82    17    32   196   187     5
   164   145   165    76   114   217   187   127   173   121
   137   126   165   176   128   105    96   169   145   153
    64   107   144   103   113   151   166   152    65   100
   217   105   154   207   173   194   144   104   197   120
   172   152    80   162    55    78   109   146   124   111
    99   110    91    72   134    98   192    89    61    79