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Are image uploads really this lossy??


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592ecbdabfefc_vrclogolocal.jpg.64f007034653cc828cfbb3b16c77649f.jpg becomes 592ecbf6d958d_vrclogoinventory.jpg.09431b04e08777f9fbf20f4422473010.jpg

on upload... or, I must be doing something wrong, right?

I reported this as a jira that includes a source .tga file and maybe more detail. To explain the images here, the baby blue background is not part of the texture; it's just to show that the texture includes the white-background circle. But what is all that black noise in the periphery? It only appears after the texture has been uploaded to Inventory (not while it's still "Local"), and only when alpha masking with the mask set at exactly 1 -- at 2, it looks fine (but that isn't good enough for this application because the noise is very apparent when the texture is used in a particle).

The only explanation that comes to mind is that the alpha channel's lowest order bit is uniquely lossy in compression -- but surely there are plenty of particle textures that don't have such stark artifacts, so I must be missing something. Right?

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Hmm. Well, using Whirly's texture, I still see the artifacts. It's true that it's not as stark, blended on a particle, as it is on an alpha-masked surface texture, but I'm still seeing it on a particle against a light background (and it does seem darker than I might expect from just 1/256th opacity, but that's just a vague, subjective impression).

FWIW, my alt sees it the same way. I also tried with a fresh object in a different sim -- purely superstitiously -- and of course it made no difference. I'm kinda stumped as to what to try next.

Edited by Qie Niangao
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Second Life 5.0.4.325124 (Second Life Release)

Actually, on very close inspection of a particle, I think I do see some faint artifacts in the transparent areas as well. But I really have to put that against a white background and zoom in all the way to make these out.

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Oh, I think I know why the particle artifact appears more opaque than it should: I'm using DROP and the copies just accumulate on top of each other, so there could be quite a few "layers" of that blended alpha, compared to a single alpha-blended surface.

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Oh, I just now checked my email to see that Dan closed the jira as expected behaviour, artifacts of compression loss.

I feel better knowing I wasn't doing something totally stupid... and since my original target was a particle, I can tweak the timing parameters and it'll be fine for this application.

And I imagine most surface texture applications can use a masking threshold > 1 and never have a problem.

Thanks for the help!

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