Assign User-defined grayscale value

I have data in matrix form and I want to assign elements in matrix specific grayscale value( 8-bit, 0 to 256) and than plot a 2D Grayscale image. The function 'mat2gray' assign 0 value to minimum and 1 to maximum but I want to have user-defined value given to elements. [for ex. if my element value is 50 I want to assign grayscale value of 0 to it irrespective whether its minimum or maximum]

[Adam]

Just create your own mapping or colourmap then. mat2gray is just a convenience function for the trivial maths of max stretching a data range to the full colourmap range.

Answer 1

[Jan]

Create a lookup table:

LUT = zeros(1, 256);
LUT(50 + 1) = 1;

Img  = randi([0, 100], 200, 100);  % Your image
Grey = LUT(Img + 1);

Now the pixels of Img with the value 50 are set to 1.0, and all others to 0.0 . Of course you can adjust LUT arbitrarily.