[BUG-226745] Alpha incorrectly implemented for PNG images

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This issue was moved to BUG from VWR-28831

when a PNG has any kind of internal alpha information (key color, or alpha channel), then the uploaded image always has an alpha channel, and the resulting special status (like priority glitches etc).

this is wrong. it violates the PNG specification which basically states that PNG images which are equal after expansion to uncompressed RGBA, are equivalent (as in, look the same). this equivalence of different ways to encode the same image is part of PNG's philosophy, and PNG optimizers like optiPNG (which make PNG files smaller) are lossless under this premise.

the correct thing to do would be to set the image to having an alpha channel iff there is any real transparency (as in, any pixel that is not fully opaque).

references: http://www.w3.org/TR/PNG/ section 4.3

http://optipng.sourceforge.net/pngtech/optipng.html

4. An extra note on losslessness

Attachments

• RedSquare.tga 2019-04-11 16:56:24
• xwjvZHsY.png 2019-04-11 16:55:25

Original Jira Fields

| Field | Value | | ------------- | ------------- | | Issue | BUG-226745 | | Summary | Alpha incorrectly implemented for PNG images | | Type | New Feature Request | | Priority | Unset | | Status | Needs More Info | | Resolution | Unresolved | | Reporter | Beware Hax (beware.hax) | | Created at | 2009-07-03T21:17:55Z | | Updated at | 2019-04-12T11:39:54Z | ``` { 'Date of First Response': '2009-07-03T16:20:44.000-0500', 'How would you like the feature to work?': '2', 'Last Triaged': '2009-12-29T13:59:00.000-0600', 'Previous Issue ID': 'http://jira.lindenlab.com/jira/browse/DEV-44683', 'Why is this feature important to you? How would it benefit the community?': '1', } ```

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WarKirby Magojiro commented at 2009-07-03T21:20:44Z

This is something I find annoying when working with textures quite a lot. An uploaded png will look completely opaque, but it will show red when using view transparent (ctrl+alt+t) and will cause alpha sorting issues when placed in front of other textures that use alpha.

In photoshop, it can simply be fixed by putting a background layer under the image. This seems an annoying and inefficient extra step, though. And forgetting to do so has resulted in a lot of wasted uploads for me.

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Ethari Hallstrom commented at 2009-07-06T16:58:17Z

Voted! I had the exact same issue as WarKirby.

It's a shame, however, that LL can't just fix the damn problem that causes the alpha sorting issues in the first place. They keep fobbing us off with excuses - this is not acceptable. No game that I know of would accept such a hideous graphical error, and it's ruining the appearance of things.

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Lynne Latte commented at 2009-10-30T11:43:18Z

This is nearly impossible to correct if the conflicting textures involve purchased buildings, etc. This results in wasted lindens on a purchase you can't use or putting up with crappy appearance.

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Strife Onizuka commented at 2009-10-30T13:29:45Z

This doesn't sound like something hard to fix (during the upload process).

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Moon Metty commented at 2009-10-30T14:47:11Z

VWR-12283 is a feature request for a checkbox ...

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Beware Hax commented at 2010-10-18T01:23:47Z

i think an automatic check is better than a checkbox. simplicity, less chance to do things wrong.

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WorkingOnIt Linden commented at 2011-12-05T22:09:23Z

This issue has not been updated in 2011 and relates to a deprecated viewer. In an effort to keep our focus on current bugs, this issue is being closed as Needs More Information. If you are still experiencing this issue in the latest viewer, please update the Affects Version/s and Environment fields then re-open.

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Beware Hax commented at 2011-12-05T22:49:56Z

reproduced in the latest version (3.2.1)

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polysail commented at 2019-04-11T21:12:23Z

Appended a 32 bit TGA texture of a red box, with an fully filled in alpha.  I can't even produce a PNG texture with an empty alpha channel, because if I ask Photoshop to save a PNG texture with transparency with an empty alpha channel it erases the empty alpha channel and gives me a 24 bit texture.

Uploading such textures on the Firestorm viewer nets a surface that is neither alpha masking / or alpha none. It simply arrives in world as a 24 bit texture.

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polysail commented at 2019-04-11T21:22:00Z, updated at 2019-04-11T21:29:49Z

Interesting, I do actually get a repro on xwjvZHsY.png

It uploads as alpha-blend on SL, despite Photoshop refusing to even acknowledge that it's an Alpha Texture to begin with.  Edit.  Nevermind it's an alpha texture.   Photoshop loads it in with alpha data.   If I convert it to a TGA the alpha channel turns up be entirely empty however.   Reuploading the TGA or PNG to SL after it's been through photoshop negates the inworld "Alpha Blending" behavior.  Yet the provided upload exhibits it.