MATLAB: .^2 does not work as expected

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Hi,
I'm doing some math calculations in a code. I noticed something strange in the code below:
a = imread('C:\tqPixels.png'); I = rgb2gray(a);
exp = I.^2
As tqPixels.png is an image with only 4 white pixels (all have 255 value), I thought that exp variable value would be each value powered to itself (255 * 255):
exp = [65025, 65025; 65025, 65025]
However, when I saw exp value in the results, it had the same values variable "I" had:
exp = [255, 255; 255, 255]
Sorry if this is very simple, but why .^2 does not work as it should?
I'm attaching the image and the code here for you to test. I really appreciate any suggestions on this.
a = imread('C:\tqPixels.png');
I = rgb2gray(a);
exp1 = I.^2;

Best Answer

I think you need to convert I to ‘double’ before doing the exponentiation on it. As it is, I believe it is ‘uint8’ type and anything above 255 is set down to just 255. Do this:
   exp1 = double(I).^2
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