MATLAB: How to find the intensity percentage in a gray scale image

find decimal value from intensity imageImage Acquisition ToolboxImage Processing ToolboxMATLAB

Dear all,

I have 8bit gray scale image "I". I want to find "X" which is the 99.5% of the maximum intensity value. So if the image has at least one white pixel (255), then "X" should be 253.725.

I tried the following code but I'm getting different answer:

I = getimage;
X = (max(I(:))/100) *99.5;

Why the value for "X" is 255 not 253.725?

Any help will be appreciated.

Meshoo

Best Answer

Meshoo - what is the answer that you are getting? 255? From your question, I think it is safe to assume that the data type for your image is an 8-bit unsigned integer. So if your maximum value is 255 then

 maxVal      = uint8(255);
 maxValBy100 = maxVal/100;  % this is now 3 because the data type is uint8
 maxValBy100*99.5           % this is now 255 since 3*99.5 is greater than the max
                            % allowed 8-bit unsigned int (255) so is capped at that 
                            % maximum

Since you are mixing doubles with 8-bit unsigned ints, then just cast the maximum value of I to a double before dividing by 100

 X = (double(max(I(:)))/100) *99.5;

and the above will return the desired 253.725. Try this and see what happens!

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The question is not clear. But let me guess:

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Or:

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Best Answer

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