hi, I am presently workin on datamarking of images using DCT. I have created the datamark first by splitting the image into 8*8 blocks and then applying DCT to each individual blocks. Then i got the marked image using IDCT. i tried saving this image using imwrite and in bmp format(the format of image i had used). the problem is when i use this image which is saved using imwrite i m unale to extract the information in the particular coefficients...Can anyone give me some ideas regarding this aspect. regds, rukmani.