COMPRESSRANGE - Compress the entries of a matrix.

Contents

Description

Compress (reduce) the range of a matrix of positive (or null) values.

Syntax

   I = COMPRESSRANGE(I);

Input/output

I : image with integer values to compress.

Credit

J.Grazzini (ISR-2/LANL)

See also

Requires: CUMSUM, DIFF, RESHAPE.

Function implementation

function I = compressrange(I)

sz = size(I);
I = I(:);

if ~(isinteger(I) || isequal(I,round(I))) || ~all(I>=0)
    error('compressrange:errorinput', ...
        'only input image with positive integer values are dealt with')
end

values = unique(I);  % sorted list of unique values
if values(1)~=0, values = [0; values];  end

check if we really have to do something

if length(values)==max(I(:))+1,  return;  end

this function ensures that the values displayed in the input image are set in sequential order 0 values in the original image are left with the label 0

A = cumsum(diff(values)-1);
values = values(2:end);
A = values - A;
% do the relabelling: compress
for l=1:length(values),    I(I==values(l)) = A(l);  end

reshape

I = reshape(I,sz);

end % end of compressrange