How to apply a quantization step to a 2D transformed image?

Hi all of you, I need some help here, my problem is how can i use quantization to the result of that code below?,knowing that the result (XDFT) is complex arry, example: XDFT(1,1)=125+ i*2562. So how values like XDFT(1,1) will be on an interval between 0 and 255.

    [filename, pathname] = uigetfile('*.bmp', 'open image');% getting a Bitmap image.
    [X,MAP]=imread(fullfile(pathname, filename));%Image reading.
    R=input('R=');%bloc size(8*8 or 16*16 or 32*32).
    XDFT= blkproc(X,[R R],'fft2');%DFT Transformation of X.

[Matt J]

I've marked-up your code to make it more readable.

[Said BOUREZG]

Thank you Matt J .

[Matt J]

You're welcome, but I hope you will also learn to do this.

Answer 1

[Matt J]

Why not quantize the real and imaginary parts? Or, like in JPEG compression, why not use the DCT, instead of the DFT, so that the block spectra are real-valued?

[Said BOUREZG]

I don't have a problem with DCT or DWT, my problem with DFT coefficients if I separate real and imaginary parts and I quantize them, the compression of them can't give a good results.

[Walter Roberson]

Why is it not possible for the compression to give good results? If you keep 5 real components and 5 imaginary components, that is as good a compression as keeping 10 real components.