HI I was trying to brighten grayscale image with I=rgb2gray(A) J = imadjust(I) . For some reason it was not working. Can anyone please tell me if there any other way? thanks

I was trying to brighten grayscale image with I=rgb2gray(A) J = imadjust(I) . For some reason it was not working. Can anyone please tell me if there any other way? thanks

[Jan]

Please explain "not working" with any details. Do you get an error message or do the results differ from your expectations?

[Ashim Chakraborty]

basically the output i am looking for is not generating. I meant to brighten up grayscale image.I think imadjust() command upgrade the contrast but will it work to brighten up the image? I dont get any error message. thanks

Answer 1

[Stephen23]

Actually imadjust can also brighten images, you just need to supply the fourth input gamma:

J = imadjust(I,[],[],gamma);

Where the documentation describes gamma: _"If gamma is less than 1, imadjust weights the mapping toward higher (brighter) output values. If gamma is greater than 1, imadjust weights the mapping toward lower (darker) output values. If you omit the argument, gamma defaults to 1 (linear mapping)"

So try some gamma values until you get one that you like.

Answer 2

[Image Analyst]

How about brighten()?

If not, then just add some offset to your image.

 brighterImage = originalImage + someOffset;

[DGM]

While the webdocs recommend brighten() in the links related to image adjustment, brighten() doesn't work on images. It works on colormaps and graphics objects in a figure. Though not practically convenient, any RGB image could be reshaped to work with it.

Acmap = reshape(im2double(A),[],3); % integer inputs are not supported!
Bcmap = brighten(Acmap,0.5);
B = reshape(im2uint8(Bcmap),size(A));

It's worth noting that contrary to the name, this is not an additive brightness adjustment tool. It's an obfuscated gamma adjustment tool.

in = linspace(0,1,100);

% simple additive "brightness" control
out_additive = min(max(in+0.15,0),1);

% a gamma control with linearized control parameter
out_gamma = brighten(in,0.5);

plot(in,out_additive); hold on
plot(in,out_gamma)
xlabel('input graylevel')
ylabel('output graylevel')
legend('additive','using brighten()','location','southeast')