On Fri, 11 May 2007 12:54:45 -0700 (PDT) Z F <[EMAIL PROTECTED]> wrote:
> > --- Miguel Lobo <[EMAIL PROTECTED]> wrote: > > > > > > > It does not matter if you add random float to a float and truncate > > or > > > trancate and add a random bit, the outcome will be exactly the same > > > sequence of bits so it does not matter, you can always add dither > > > later. > > > > > > Write it out... > > > > > > trun(signal + noise) = trun(signal) + noise' > > > > > > notice that noise' is not the same as noise, but the equality holds > > > so one can do what can not be done -- remove undesired harmonic > > > after truncation. > > > > > > The problem is that there is no way of calculating noise' after the > > truncation. You would need the information that was lost in the > > truncation. > > > > I think a visual example might be easier to understand. In the > > Wikipedia > > page for dither http://en.wikipedia.org/wiki/Dither they have a > > series of > > pictures of a cat. The first one is the original high-depth > > photograph. In > > the second picture, truncation has been applied without dithering and > > you > > can see big flat areas of uniform color. How can you know which was > > the > > original shade of a pixel in those flat areas? You can't. In the > > third > > picture, truncation has been applied with dithering. You can see > > that > > although the palette of the third picture is the same as that of the > > second, > > the "average" color of each area has been much better preserved. > > There are > > more bright pixels where the original picture was brighter, and fewer > > where > > it was darker. To do that you need the information in the original > > picture. > > > No, you do not... :) Ever heard of texture synthesis? All you need > is statistical properties, not the signal itself to generate which > looks like a cat. So, it can be done without the original :) Since the > main features of the signal are preserved after truncation (otherwise > it would have been useless), it should be enough to synthesize noise'. Yes, we can truncate original picture to three chars - 'cat', but it have much less useful info about original object ;) Any truncate incorrigible, with dithering we have much less loss, then without. Any synthesis - fake, it improve quality, but lack of similarity with original. _______________________________________________ fluid-dev mailing list fluid-dev@nongnu.org http://lists.nongnu.org/mailman/listinfo/fluid-dev
