Those 14 bits (part 2)

Started Jan 19, 2014 | Discussions thread
seachicken2000 Veteran Member • Posts: 3,214
Re: 2nd attempt to reproduce (A7r vs D800) [successful]

GaryW wrote:

If it's known exactly what situation produces the artifacts, I wonder if when the problem data is unpacked, could that block be "dithered" or smoothed or something to reduce the artifacting pattern? I was thinking about what Jay said about adding noise, and I'm just wondering if some "random noise" would mitigate the problem?

I am thinking the same thing. If you have a set of pixels that vary +/- n levels in the original data, and you encode them all to the same value, it seems odd that you'd want to decode them all to the same value. If you decode like this, you will get positerization in the final output.

It seems more realistic to spread the decoded values over a +/- n level range, just like they were originally. This could be done simply by placing a probability distribution on the range, and sampling the values.

Decoding this way:

  • If what was removed was only noise, and you have a good model of this noise, you can replace the noise that was removed with noise of the same character, and the decoded image should look just like the original.
  • If you removed some signal along with the noise, then when you decode, you will fill in the signal+noise that you removed, with just noise.

Decoding the using the (usual?) positerization preserving method:

  • In both cases you will fill in the noise (or noise+signal) that you removed with nothing at all; ugly characteristics of the encoded form of the image (a compressed representation not intended to be seen by the viewers of the photograph) will find their way directly into the final output; the decoded image will contain positerization.
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