carniphage Posted October 30, 2019 Share Posted October 30, 2019 Hi, I am using Affinity Photo to replace Photoshop for game development work. One common workflow, when authoring textures for games, is to use the alpha channel to define some material property (rather than transparency). In the Unity game engine, alpha is used for the "smoothness" channel. In Affinity Photo, it is actually quite easy to use the channel panel to paste a smoothness image, put in into a spare channel, then move it into the alpha. So far, so good. HOWEVER... When the file is exported, the R,G and B pixel values appear to be multiplied by the corresponding alpha value. This makes the export unusable, because while the alpha is correct, the R,G and B are suddenly not the values which were authored. I tried to see if all exports formats did the same thing. This issue happens whether the document has a transparent or solid background, or whether the exporter is PNG, TGA or TIFF. I can understand why this behaviour might be the default, but it means that this very commonplace channel-packing workflow is not possible using Affinity Photo. I would very much like to request a feature where export "premultiply" behaviour could be turned-off. Perhaps with an export checkbox. Or perhaps off by default on transparent background documents. kirk23 and fde101 2 Quote Link to comment Share on other sites More sharing options...
fde101 Posted October 31, 2019 Share Posted October 31, 2019 Hi @carniphage, welcome to the forums! This issue has been brought up on a few other threads and I certainly agree this option should be available. carniphage 1 Quote Link to comment Share on other sites More sharing options...
Mark Oehlschlager Posted November 1, 2019 Share Posted November 1, 2019 @carniphage Does this video help? Quote Link to comment Share on other sites More sharing options...
fde101 Posted November 3, 2019 Share Posted November 3, 2019 On 11/1/2019 at 1:57 AM, Mark Oehlschlager said: Does this video help? No, that has nothing to do with the issue of the alpha channel being pre-multiplied. Quote Link to comment Share on other sites More sharing options...
carniphage Posted November 3, 2019 Author Share Posted November 3, 2019 This was the first video I looked at. If you watch it, it shows a workflow where the R/G and B channels are constructed - but the alpha channel is left solid. (In fact, the video advises it). The problem happens when the alpha channel is not solid, which is a requirement for these workflows. If that is done, then on export, the values in the R,G and B channels are changed. Quote Link to comment Share on other sites More sharing options...
Fran J. NS Posted February 27, 2021 Share Posted February 27, 2021 On 30/10/2019 at 16:02, carniphage said: I'm in your same situation. I can't export alpha correctly. Any solution in 2021 by affinity team? Thanks. Quote Link to comment Share on other sites More sharing options...
AutumnPioneer Posted November 17, 2022 Share Posted November 17, 2022 I REALLY need this feature too! Allowing other channels while the alpha channel is locked too would help so much Quote Link to comment Share on other sites More sharing options...
kirk23 Posted November 18, 2022 Share Posted November 18, 2022 Affinity photo exports those files with alpha channel just right . V2 at least. In v1 it was also perfectly possible with a simple trick. The problem is not what Affinity export. The problem is that when you open the file back to Affinity photo it multiplies black over rgb values of pixels having perfectly zero alpha, Only over those ones. End this needs to be fixed for sure. ps. V2 doesn't do it for exr files although. floating point images being opened perfectly right too, without those black holes Quote Link to comment Share on other sites More sharing options...
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