The instructions are as follows: A MATLAB script for accomplishing this is to be found under “DCT and Image Compression" at: http://www.mathworks.com/help/images/discrete-cosine-transform.html?refresh=true The basic procedure is as follows: 1.) Break an image-pixel array down into smaller blocks, e.g. 8 8 (or 16 16) pixels, 2.) perform a discrete cosine transform (dct) on these smaller blocks, 3.) apply a mask, consisting of an 88 array of zeros and ones, using array multiplication on the above dct block in order to eliminate certain high-frequency components, 4.) use the inverse discrete cosine transform (idct) to reconstruct 8 8 image blocks, and 5.) reassemble the blocks into a new image. This HW problem involves the following steps: a.) Create your own function imcompress.m based on this script that will use 88 blocks, and will accept the name and type of an image together with a matrix representing the mask as input arguments2. b.) Use comments before each major step in the program, explaining exactly what it accomplishes, identifying user-defined functions and distinguishing these from built-in MATLAB functions. Note: 2The given script works only for 2D image arrays whose size is a multiple of the basic block size [8 8]. Hence, you will need to process each RGB color plane separately, e.g. using a for-loop, and to trim the input array down to the nearest multiple of 8, e.g. using a command such as new = old-rem(old, 8).
Here is what I have so far.
function imcompress(fig, fmt, mask ) P = imread(strcat(fig, '.', fmt)); P = im2double(P); siz = size(P) - rem(size(P), 8); for c = 1:3 I = P(1:siz(1), 1:siz(2), c); Q = dctmtx(8); fund = @(R) Q * R.data * Q'; z = blockproc(I, [8 8], fund); %funm = mask .* R z2 = blockproc(z, [8 8], @(R) mask .* R.data); funid = @(R) Q' * R.data * Q; I2 = blockproc(z2, [8 8], funid); P2 = I2(1:siz(1), 1:siz(2), c); end imshow(P2), figure, imshow(P) end
I am getting the error
>> imcompress2('maid','tiff',mymask(8)) Index exceeds matrix dimensions.
Error in imcompress2 (line 14) P2 = I2(1:siz(1), 1:siz(2), c);
and I'm not sure why. Any help would be amazing. the program runs if i comment that line, but then i don't think it's assembled into a new image, because it is a grayscale image that is created.
