Author Topic: TGVDN "What looks good and What looks bad"  (Read 457 times)

Offline tdgm

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TGVDN "What looks good and What looks bad"
« on: 2018 February 12 21:18:47 »
Hello everyone

I understand you are attempting to get a look that is not plastic or fake but a picture is worth a thousand words. I am having a lot of trouble determining exactly what is good and what is bad visually. Would be appreciated if someone good upload  examples of both.

Thanks for any assistance anyone can supply.


Steve

Offline ngc1535

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Re: TGVDN "What looks good and What looks bad"
« Reply #1 on: 2018 February 12 22:09:12 »
Of course that is an entirely subjective question. However, without showing lots of pictures- I think the "answer" depends on the data itself.
To be a "good" image it generally has a self-consistency in chrominance, luminance, and graininess. The point of the question is whether a
smoothing process (noise reduction) results in pixel-to-pixel relationships in low S/N that relate to their high
S/N counterparts. The better the transition from one to the other, usually the better the visual appearance of the image's internal
self-consistency.

Perhaps also important is that high signal areas can have many contiguous pixels of equal values (or values that vary as a smooth gradient).
 Low SNR areas (or background-like values) *naturally* show more variation. If variation in the low signal areas is minimized by smoothing-
and making many contiguous pixels have nearly equal values (or gradients)- this effectively promotes the background to be more high SNR like.
This means the background visually becomes a "thing" and not a natural background with variation as expected. This is the "waxy" bit that I think is often described.
This is why leaving some variation in background is good- it really is the form of the variation that is the key. We seek to find patterns in the noise. If you don't have
"good" variation- our brains say "I see the pattern (the thing)"  where we really want to ignore it compared to other bits.

So it wasn't a thousand words- but the words above might be useful when looking at an example picture.

-adam

Offline John_Gill

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Re: TGVDN "What looks good and What looks bad"
« Reply #2 on: 2018 February 13 08:58:41 »
Ngc1535 - great answer.  For my 2c worth, I try to push each process too much and/or too little, just to see the result.  That gives me a in-between starting point.  Then tweak the process from there.

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John
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