How to compress an image?

I'm trying to Compress an image by using Run Length coding and Huffman coding but I get errors Please would you like to help by showing me the correct codes

This my codes:

EDU>> D=imread('M.png');

F=im2double(D);

symbols = unique(F(:));

counts = hist(F(:), symbols);

p = double(counts) ./ sum(counts);

r(p:q) = [y(1:i, j); eob];

count= count + i + 1; %and add to output vactor

F((count+1):end) = []; %delete unused portion of B

y.size=uint16([xm xn]);

y.numblocks = uint16(xb);

y.quality = uint16(quality * 100);

y.huffman = mat2huff(B)

Warning: Colon operands must be real scalars. Undefined function 'y' for input arguments of type 'double'.