JPEG steganography If you want to save your image to jpeg, you have to follow the jpeg encoding process. Unfortunately, papers most I’ve read say don’t do it justice. The complete process is the following (wiki summary of a 182-page specifications book): RGB to YCbCr conversion (optional), subsampling of the chroma channels (optional), 8×8 block … Read more
Well, I did a bit of reading and my original question seems to be an instance of wishful thinking. Basically, it’s not possible to get the DCT coefficients from H.264 video frames for the simple reason that H.264 doesn’t use DCT. It uses a different transform (integer transform). Next, the coefficients for that transform don’t … Read more
Here is mine computation of 1D FDCT and IFDCT by FFT with the same length: //————————————————————————— void DFCTrr(double *dst,double *src,double *tmp,int n) { // exact normalized DCT II by N DFFT int i,j; double nn=n,a,da=(M_PI*(nn-0.5))/nn,a0,b0,a1,b1,m; for (j= 0,i=n-1;i>=0;i-=2,j++) dst[j]=src[i]; for (j=n-1,i=n-2;i>=0;i-=2,j–) dst[j]=src[i]; DFFTcr(tmp,dst,n); m=2.0*sqrt(2.0); for (a=0.0,j=0,i=0;i<n;i++,j+=2,a+=da) { a0=tmp[j+0]; a1= cos(a); b0=tmp[j+1]; b1=-sin(a); a0=(a0*a1)-(b0*b1); if (i) … Read more