NotMyFault Posted August 25, 2021 Share Posted August 25, 2021 (edited) Hi, i created a test file to compare how alpha blends in different situations, especially "color opacity vs layer opacity". The file contains 16 tiles 4 "large" tiles showing top: vector shapes, bottom: fill layers, left: raw, right: copy of left rasterized & tim 4 "small" tiles, showing left: red left color opacity / layer opacity : 50 / 100, right 100 / 50 blue top 50 / 100, bottom 100 / 50 As visible, the fill layer blend result differs from vector blend result, and rasterized layers blend results (bottom left corner) I strongly assume a bug with fill layers alpha blending - except someone from Affinity can provide a good explanation in layman's terms (or exact math formula) color vs layer opacity vector vs fill bug.afphoto Edited August 25, 2021 by NotMyFault Quote Mac mini M1 A2348 | Windows 10 - AMD Ryzen 9 5900x - 32 GB RAM - Nvidia GTX 1080 LG34WK950U-W, calibrated to DCI-P3 with LG Calibration Studio / Spider 5 iPad Air Gen 5 (2022) A2589 Special interest into procedural texture filter, edit alpha channel, RGB/16 and RGB/32 color formats, stacking, finding root causes for misbehaving files, finding creative solutions for unsolvable tasks, finding bugs in Apps. Link to comment Share on other sites More sharing options...
NotMyFault Posted August 25, 2021 Author Share Posted August 25, 2021 (edited) To give this another direction: It would be really really great if Affinity (James?) would provide some tutorials how all this combines: Color opacity Layer opacity Fill opacity (from Layer FX) Blend differences wrt alpha /opacity of Fill layers vs. all other types of layers And other areas or arcane secrets like Brush Opacity Brush Flow Brush Accumulation Fun explosion: In combination with all these alpha blend options mentioned above And more arcane secrets of layer blending layers following normal alpha compositing blend rules (pixel, curves, ...) layers able to overwrite blend rules (PT Filter, alpha-impacting adjustments levels , curves, channel mixer: just set/define new alpha value) How all this integrates layers flat atop each other layers nested to description of ordinary layers layers nested to thumbnail of ordinary layers (masking / clipping position) layers nested to description of group layers layers nested to thumbnail of group layers layers nested to stacking groups (alpha reduced to 0 / 1) Edited August 25, 2021 by NotMyFault BeauRX 1 Quote Mac mini M1 A2348 | Windows 10 - AMD Ryzen 9 5900x - 32 GB RAM - Nvidia GTX 1080 LG34WK950U-W, calibrated to DCI-P3 with LG Calibration Studio / Spider 5 iPad Air Gen 5 (2022) A2589 Special interest into procedural texture filter, edit alpha channel, RGB/16 and RGB/32 color formats, stacking, finding root causes for misbehaving files, finding creative solutions for unsolvable tasks, finding bugs in Apps. Link to comment Share on other sites More sharing options...
Staff Gabe Posted August 26, 2021 Staff Share Posted August 26, 2021 Hi @NotMyFault, I will get this logged and see if it's right or not, but I'm afraid we will not be providing any formulas for how this is calculated. Quote Link to comment Share on other sites More sharing options...
NotMyFault Posted August 26, 2021 Author Share Posted August 26, 2021 Maybe i found a probable cause: When reducing layer opacity of fill layer to 50%, it becomes much lighter vs. all other methods. You can spot this by disabling all red layers. maybe related to (missing / double) gamma correction in blend formula. 0.7^2.2 roughly equals 0.5 if i change opacity to .7 it gives expected color Quote Mac mini M1 A2348 | Windows 10 - AMD Ryzen 9 5900x - 32 GB RAM - Nvidia GTX 1080 LG34WK950U-W, calibrated to DCI-P3 with LG Calibration Studio / Spider 5 iPad Air Gen 5 (2022) A2589 Special interest into procedural texture filter, edit alpha channel, RGB/16 and RGB/32 color formats, stacking, finding root causes for misbehaving files, finding creative solutions for unsolvable tasks, finding bugs in Apps. Link to comment Share on other sites More sharing options...
NotMyFault Posted August 26, 2021 Author Share Posted August 26, 2021 Only a Fill Layer opacity will transform the alpha channel with a gamma of 2.0 which seems to be wrong. As far as i know, alpha channels does not apply gamma correction, see comments by Gabe and: https://en.wikipedia.org/wiki/Alpha_compositing Note that only the color components undergo gamma-correction; the alpha channel is always linear. Quote Mac mini M1 A2348 | Windows 10 - AMD Ryzen 9 5900x - 32 GB RAM - Nvidia GTX 1080 LG34WK950U-W, calibrated to DCI-P3 with LG Calibration Studio / Spider 5 iPad Air Gen 5 (2022) A2589 Special interest into procedural texture filter, edit alpha channel, RGB/16 and RGB/32 color formats, stacking, finding root causes for misbehaving files, finding creative solutions for unsolvable tasks, finding bugs in Apps. Link to comment Share on other sites More sharing options...
IPv6 Posted August 26, 2021 Share Posted August 26, 2021 1 hour ago, NotMyFault said: As far as i know, alpha channels does not apply gamma correction, see comments by Gabe Still, they are applied - in RGB32 mode // its an unfortunate decision made by Serif Quote Link to comment Share on other sites More sharing options...
NotMyFault Posted August 26, 2021 Author Share Posted August 26, 2021 2 hours ago, IPv6 said: Still, they are applied - in RGB32 mode // its an unfortunate decision made by Serif Maybe we are talking about completely different topics. I strongly assume Affinity don't use Gamma correction on Alpha channel for layer blending in any color mode - except the (faulty) case of fill layers. Specifically what is explained in the wikipedia link about Alpha Composting. I did not relate to other situations, e.g. converting between 8/16 and 32 bit modes, or channels panels / channels mixer etc. I've read your post in the linked thread, but couldn't follow your argumentation. I will try to make some artificial test documents on my own, this helps me to understand. IPv6 1 Quote Mac mini M1 A2348 | Windows 10 - AMD Ryzen 9 5900x - 32 GB RAM - Nvidia GTX 1080 LG34WK950U-W, calibrated to DCI-P3 with LG Calibration Studio / Spider 5 iPad Air Gen 5 (2022) A2589 Special interest into procedural texture filter, edit alpha channel, RGB/16 and RGB/32 color formats, stacking, finding root causes for misbehaving files, finding creative solutions for unsolvable tasks, finding bugs in Apps. Link to comment Share on other sites More sharing options...
NotMyFault Posted June 17, 2023 Author Share Posted June 17, 2023 Bump. still unfixed in V2.1 Quote Mac mini M1 A2348 | Windows 10 - AMD Ryzen 9 5900x - 32 GB RAM - Nvidia GTX 1080 LG34WK950U-W, calibrated to DCI-P3 with LG Calibration Studio / Spider 5 iPad Air Gen 5 (2022) A2589 Special interest into procedural texture filter, edit alpha channel, RGB/16 and RGB/32 color formats, stacking, finding root causes for misbehaving files, finding creative solutions for unsolvable tasks, finding bugs in Apps. Link to comment Share on other sites More sharing options...
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