user3611: I'm going to compress a video but I have one problem.
Is a frame with a bit(last bit) of each color(RGB) changed unacceptable or distinguishable from the original one in HD?

user2836: It is unlikely to be noticeable.  This is basically the principal on which steganography operates.  It changes the least significant bits in images and video such that there is not a noticeable change in the final image, however software can later pull out the data without it being obvious that the data was there.  Without access to the original image it is quite difficult for even a computer to know that the change occurred.  The NSA and security professionals in general have put considerable time and resources in to trying to figure out good ways to identify steganographic messages.

user3908: Unacceptable is in the eye of the watcher, so that part is tough to answer.
Distinguishable is easier: yes, there will be a difference. It will not be obvious in every frame or circumstance, but it will be there. If you simply truncate the lowest bit, it will raise the noise floor and the effect will be most evident in low light areas. So, it will look worse, but how much worse, and whether it's acceptable, depend on the particulars.

3611: <p>I'm going to compress a video but I have one problem.</p>

<p>Is a frame with a bit(last bit) of each color(RGB) changed unacceptable or distinguishable from the original one in HD?</p>
 2836: <p>It is unlikely to be noticeable.  This is basically the principal on which steganography operates.  It changes the least significant bits in images and video such that there is not a noticeable change in the final image, however software can later pull out the data without it being obvious that the data was there.  Without access to the original image it is quite difficult for even a computer to know that the change occurred.  The NSA and security professionals in general have put considerable time and resources in to trying to figure out good ways to identify steganographic messages.</p>
 3908: <p>Unacceptable is in the eye of the watcher, so that part is tough to answer.</p>

<p>Distinguishable is easier: yes, there will be a difference. It will not be obvious in every frame or circumstance, but it will be there. If you simply truncate the lowest bit, it will raise the noise floor and the effect will be most evident in low light areas. So, it will look worse, but how much worse, and whether it's acceptable, depend on the particulars.</p>
