From: Daniel Egger <de@xxxxxxxxxx> Date: Sun, 27 Feb 2005 16:03:14 +0100 this is my suggested patch for getting the speeds improvements as mentioned in the other thread by having a thread-local PRNG initialized with a seed from the still existing blend tool local RNG. It looks bigger than it is because I took the liberty to remove the nasty special casing on the existence of the RNG inside the innermost loop because we now have it outside already. There seems to be more room for obvious optimisations in the loops. Also I would recommend splitting the two cases into two separate functions to make the code easier to read, and remove more conditionals. PS: If this is okay, I'd do exactly the same for the gray blending stuff... In addition to being very slow, this will also yield noisy results. There are a lot of dither algorithms that are both much faster and yield better results. While you may not need full-blown Floyd-Steinberg or EvenTone dithering for this purpose (and they're hard to use in a multi-threaded fashion), a simple dither matrix is fast, free of most artifacts, trivial to parallelize (you're only reading from the matrix, so no serialization is necessary), and reasonably low noise. In Gutenprint we have several precomputed matrices, designed for 1:1, 2:1, and 4:1 aspect ratios. You would need only a 1:1 ratio matrix. Also, our matrices are large (about 64K elements each, since they need 16 bit resolution), but you wouldn't need anything that big. There's a very simple iterated matrix that can generate any desired power of 2 matrix size (which makes for even faster lookup), but it does suffer from patterning. That may not matter for this purpose, since the steps are very small. We use the same matrix for all color channels, but offset the starting address for each channel to decorrelate the channels. Let me know if you're interested. -- Robert Krawitz <rlk@xxxxxxxxxxxx> Tall Clubs International -- http://www.tall.org/ or 1-888-IM-TALL-2 Member of the League for Programming Freedom -- mail lpf@xxxxxxxxxxxx Project lead for Gimp Print -- http://gimp-print.sourceforge.net "Linux doesn't dictate how I work, I dictate how Linux works." --Eric Crampton
