OK thanks for specifying what filters are doing this . I just did a test with a rect that was just under half black half white with 2.2 . Using gaussian blur repeatedly it ended up an even grey (114,114,114) after about 20 cntl-F reps. After 100 or so it was at 112. It should have been lighter than 128 , this does seem to be consistant with a rounding error. gg. On Wed, 25 Apr 2007 01:08:21 +0200, Campbell Barton <cbarton@xxxxxxxxxx> wrote: > just did a simple test > > * 16x16 rgb image > * select half (vertically in my case) and fill in > * run the Gaussian blur, 1 blur pixel > * Hold Ctrl+F to rerun the filter many times > > - Image will eventually turn black > - Happens for RLE and IIR > > If its a rounding error, you could see if theres some way to give a more > accurate result (cast to float?) - you probably alredy do that.. > > At worst, you could dither so every second pixel rounds up. > > > gg@xxxxxxxxxxx wrote: >> On Tue, 24 Apr 2007 20:57:43 +0200, Sven Neumann <sven@xxxxxxxx> wrote: >> >>> Hi, >>> >>> On Wed, 2007-04-25 at 02:41 +1000, Jasper Schalken wrote: >>>> This is what I thought was a bug (I posted >>>> herehttp://bugzilla.gnome.org/show_bug.cgi?id=432978) but Sven Neumann >>>> says I should discuss it on here first. >>> Your video shows the blur tool being used on large areas of black color >>> and small areas of white color. The average of this is a dark gray. Now >>> when you continue to blur, you are mixing a dark gray with black. If >>> you >>> go further, you end up with all black. >>> >>> But there could very well be rounding errors in the blur tool code. >>> There are even most definitely rounding errors as we are only working >>> with 8bit per channel and rounding errors are unavoidable then. But >>> please take a look at the code and see if there's anything we could >>> change to improve this. >>> >>> >>> Sven >> >> Jasper , your bug says: >> >>>> It's algorithm >>>> appears to favour dark colours when they are included in the blur. >> >> Why do you say that? Does it still favour dark colours if the image is >> predominantly white? >> >>>> From my understanding, the average lightness of a given image should >>>> always >>>> remain constant as it is blurred. >> >> What is your understanding , of what blur tool? >> Is there some specific blur algorithm that you believe does preserve >> lightness or is this just an assumption you were making? >> >> Maybe you could be more precise about what blur you are refering to , >> there are several IIRC. >> >> Please try to be a little more specific about what you are reporting. >> >> Thanks. >> _______________________________________________ >> Gimp-developer mailing list >> Gimp-developer@xxxxxxxxxxxxxxxxxxxxxx >> https://lists.XCF.Berkeley.EDU/mailman/listinfo/gimp-developer >> > > _______________________________________________ Gimp-developer mailing list Gimp-developer@xxxxxxxxxxxxxxxxxxxxxx https://lists.XCF.Berkeley.EDU/mailman/listinfo/gimp-developer
