On Sun, Jun 5, 2016 at 5:14 PM, Gez <listas@xxxxxxxxxxxx> wrote: >> There is also flipping to/from formats with alpha. Pre-multiplied and >> non-premultiplied alpha. As well as flips to/from higher and lower >> bit-depths as well as to/from CIE Lab. By necessity of the operations >> involved, working on linear data is another one of these constraints >> that should be fulfilled. Whenever possible the developer/designer of >> image processing algorithms should be burdened with reducing the >> number of parameters, as well as sticking with good defaults - making >> efficient work-flows possible. If you continue calling it "babl >> flips" >> I will start calling your non-flipping-babl a lobotomized babl - you >> could also collapse "RaGaBaA float" into "RGBA float" along with >> "R'G'B'A float" to make babl even less capable of providing internal >> color / pixel-representation management for GEGL and thus GIMP and >> other applications using GEGL. Before scaling or blurring an image a >> user would then have to run a pre-multiply filter and after-wards >> un-premultiply filter. > > The fully automatic choice of alpha association is not always the best > way to go. > Sure, there are many documented cases where you know exactly what's the > most adequate association, but then there are also cases (which are not > corner cases at all) that completely fall apart with an automatic > selection. > For instance, take an EXR file with luminescent transparent pixels. > That's a perfectly valid case that is used extensively in VFX to > composite fire, light effects and any kind of emissive phenomena that > produce light but don't occlude light from the background. > It's important to note that what I mention is not a hack used by > artists at all. It's a valid alpha compositing situation described both > in the original porter-duff paper and the EXR specs. > If you feed that data to a program that decides a strategy of alpha > association, the most probable outcome is that the information in > pixels with zero alpha is discarded. > There is an infamous thread at Adobe Forums that had the most renowned > imagers ranting about how Photoshop was screwing image data because > programmers decided for users and made assumptions. > > That's why it's important to know what artists will do with your > software before making such assumptions. > I'm not saying that every single option in a graphics program should > come with a toggle, but you can't choose for users if you don't know > what they need. babl being able to deal with pre-multipled/associated and non-premultiplied / non-associated alpha/transparency and know if a buffer contains one or the other is a neccesary for being able to make the choice of doing things automatically or not in GEGL/GIMP ; remove this capabilitity from babl - like removing the capability to request RGB data in a linear variant of the used RGB color space, removes the ability to deal with thing automatically and requires full manual control by the operator. /pippin - digital media artist and toolsmith _______________________________________________ gimp-developer-list mailing list List address: gimp-developer-list@xxxxxxxxx List membership: https://mail.gnome.org/mailman/listinfo/gimp-developer-list List archives: https://mail.gnome.org/archives/gimp-developer-list
