[Gimp-developer] Dithering
Hi all, Just installed gimp-2.0pre1 ;) I've scanned some jpeg images with a 24bit depth. Some of them are old photographies in blackwhite that show 'bands' when are displayed on a 16 bit depth display. After digging in the menus i noticed that the image could be transformed to a indexed pallete, with a Floyd-Steinberg dithering, but that did not solve nothing, the maximum number of colors cannot be set to more that 256 :-/. Is there another way to dither an image in gimp? Programs like gqview, an image viewer, use the dither algorithms bundled with gdx_pixbuf in gtk2, and they work perfectly with the same images. Why cannot the gimp do the same quality dithering if it's using the same library? Thanks, -- David Gómez The question of whether computers can think is just like the question of whether submarines can swim. -- Edsger W. Dijkstra ___ Gimp-developer mailing list [EMAIL PROTECTED] http://lists.xcf.berkeley.edu/mailman/listinfo/gimp-developer
Re: [Gimp-developer] Dithering
Hi David, David Gómez wrote: I've scanned some jpeg images with a 24bit depth. Some of them are old photographies in blackwhite that show 'bands' when are displayed on a 16 bit depth display. This is a normal phenomenon when moving to higher bitdepths. Unless you're talking about 16 bits in total, and not 16 bits per channel, in which case I'd be a bit mystified... After digging in the menus i noticed that the image could be transformed to a indexed pallete, with a Floyd-Steinberg dithering, but that did not solve nothing, the maximum number of colors cannot be set to more that 256 :-/. Floyd-Steinberg dithering is basically a way to approximate more colors with a smaller palette... it does not actually do anything like what you are expecting (as you have noticed). Is there another way to dither an image in gimp? Have you tried blurring the image with a radius of 0.5 or 1.5 pixels? This sometimes works quite well. Programs like gqview, an image viewer, use the dither algorithms bundled with gdx_pixbuf in gtk2, and they work perfectly with the same images. Why cannot the gimp do the same quality dithering if it's using the same library? Oh, I see what you mean, I think - you're talking about the rendering of the data, you don't actually want to change the underlying data, you want it to look better. Is that right? If that's the case, then I'm afraid the answer is that I don't know. I thought we used a GdkPixbuf, so if we don't I'm stumped :) Cheers, Dave. -- David Neary, Lyon, France E-Mail: [EMAIL PROTECTED] ___ Gimp-developer mailing list [EMAIL PROTECTED] http://lists.xcf.berkeley.edu/mailman/listinfo/gimp-developer
Re: [Gimp-developer] Dithering
On Wed, Jan 07, 2004 at 09:43:09PM +0100, Sven Neumann wrote: Hi, David G??mez [EMAIL PROTECTED] writes: I've scanned some jpeg images with a 24bit depth. Some of them are old photographies in blackwhite that show 'bands' when are displayed on a 16 bit depth display. After digging in the menus i noticed that the image could be transformed to a indexed pallete, with a Floyd-Steinberg dithering, but that did not solve nothing, the maximum number of colors cannot be set to more that 256 :-/. Is there another way to dither an image in gimp? Programs like gqview, an image viewer, use the dither algorithms bundled with gdx_pixbuf in gtk2, and they work perfectly with the same images. Why cannot the gimp do the same quality dithering if it's using the same library? The GIMP display canvas uses the dithering routines from GdkRGB which is probably what you are refering to. Of course this does only affect the display, not the image data. I am not sure but I think I remember a plug-in that could apply dithering to RGB images w/o converting to Indexed colors. Actually, gqview defaults to GDK_RGB_DITHER_NORMAL whereas gimp uses GDK_RGB_DITHER_MAX always, which should theoretically do a better job. Maybe you could put up a sample image somewhere so we can see what exactly the problem is? -Yosh ___ Gimp-developer mailing list [EMAIL PROTECTED] http://lists.xcf.berkeley.edu/mailman/listinfo/gimp-developer
Re: [Gimp-developer] Dithering
Hi David ;), This is a normal phenomenon when moving to higher bitdepths. Unless you're talking about 16 bits in total, and not 16 bits per channel, in which case I'd be a bit mystified... Yes, i meant 16 bits per channel ;) Floyd-Steinberg dithering is basically a way to approximate more colors with a smaller palette... it does not actually do anything like what you are expecting (as you have noticed). Yup, i already noticed that. Maybe i'm wrong, so please correct me, but the Floyd-Steinberg is implemented by the gimp, and the dithering in gdk_pixbuf (the paramater XlibRgbDither to functions like gdk_pixbuf_draw) are different things, isn't it? Have you tried blurring the image with a radius of 0.5 or 1.5 pixels? This sometimes works quite well. I've tried it without success. The bands are too visible to be removed with a blur filter... Programs like gqview, an image viewer, use the dither algorithms bundled with gdx_pixbuf in gtk2, and they work perfectly with the same images. Why cannot the gimp do the same quality dithering if it's using the same library? Oh, I see what you mean, I think - you're talking about the rendering of the data, you don't actually want to change the underlying data, you want it to look better. Is that right? Yes, i want it to look better, and have the option to save the dithered image ;). Gqview does a dithering pass on the image, and the image looks great. I looked in the sources and saw that it doesn't implements any dithering algorithm, it just uses the underlying gdk_pixbuf dithering support. If that's the case, then I'm afraid the answer is that I don't know. I thought we used a GdkPixbuf, so if we don't I'm stumped :) I know that the Gimp is using GdkPixbuf, that's why i'm asking why it doesn't do a better dithering ;) cheers, -- David Gómez The question of whether computers can think is just like the question of whether submarines can swim. -- Edsger W. Dijkstra ___ Gimp-developer mailing list [EMAIL PROTECTED] http://lists.xcf.berkeley.edu/mailman/listinfo/gimp-developer
Re: [Gimp-developer] after the prerelease
Sven Neumann wrote: Hi, OK, the prerelease is out and the first bugs were found and fixed. After the prerelease is before the prerelease. We still have about 70 bugs on the 2.0 milestone. Our goal should now be to target this list. Not all these bugs need to be fixed before 2.0. A few, especially feature requests, can be postponed to 2.2. At some point we can also move some remaining minor problems on the 2.0.1 milestone. But all these bug reports need to be revisited. So if you have some spare time, please do a query on the 2.0 milestone and check if you can comment on some of these. Some links that are relevent, just to make things a little easier for everyone. The bugzilla query page for the prerelease. There is a bug in the query page, it seems, and the milestone is not properly read from the CGI query string. You will have to input the milestone (2.0) by hand. http://bugzilla.gnome.org/query.cgi?product=GIMPbug_status=UNCONFIRMEDbug_status=NEWbug_status=ASSIGNEDbug_status=NEEDINFObug_status=REOPENEDbug_severity=blockerbug_severity=criticalbug_severity=majorbug_severity=normalbug_severity=minorbug_severity=trivialbug_severity=enhancementtarget_milestone=2.0email1=emailtype1=substringemailassigned_to1=1email2=emailtype2=substringemailreporter2=1changedin=chfieldfrom=chfieldto=Nowchfieldvalue=short_desc=short_desc_type=substringlong_desc=long_desc_type=substringbug_file_loc=bug_file_loc_type=substringstatus_whiteboard=status_whiteboard_type=substringkeywords=keywords_type=anywordsop_sys_details=op_sys_details_type=substringversion_details=version_details_type=substringnamedcmd=gimp+pre-2.0+blockersnewqueryname=gimp+2.0+blockersorder=Reuse+same+sort+as+last+timeform_name=query The bugzilla bug list for pre-2.0 http://bugzilla.gnome.org/buglist.cgi?product=GIMPbug_status=UNCONFIRMEDbug_status=NEWbug_status=ASSIGNEDbug_status=NEEDINFObug_status=REOPENEDbug_severity=blockerbug_severity=criticalbug_severity=majorbug_severity=normalbug_severity=minorbug_severity=trivialbug_severity=enhancementemail1=emailtype1=substringemailassigned_to1=1email2=emailtype2=substringemailreporter2=1changedin=chfieldfrom=chfieldto=Nowchfieldvalue=short_desc=short_desc_type=substringlong_desc=long_desc_type=substringbug_file_loc=bug_file_loc_type=substringstatus_whiteboard=status_whiteboard_type=substringkeywords=keywords_type=anywordsop_sys_details=op_sys_details_type=substringversion_details=version_details_type=substringnamedcmd=gimp+2.0+blockerscmdtype=runnamednewqueryname=order=Reuse+same+sort+as+last+timeform_name=query These should both be one one line, so edit accourdingly -- Dan ___ Gimp-developer mailing list [EMAIL PROTECTED] http://lists.xcf.berkeley.edu/mailman/listinfo/gimp-developer
Re: [Gimp-developer] Dithering
Hi Yosh ;), The GIMP display canvas uses the dithering routines from GdkRGB which is probably what you are refering to. Of course this does only affect the display, not the image data. I am not sure but I think I remember a plug-in that could apply dithering to RGB images w/o converting to Indexed colors. Actually, gqview defaults to GDK_RGB_DITHER_NORMAL whereas gimp uses GDK_RGB_DITHER_MAX always, which should theoretically do a better job. It should, certainly. Maybe you could put up a sample image somewhere so we can see what exactly the problem is? You're right, that would be the best. Please get it from: http://david.pleyades.net/Explorar0044.jpg It's has a size of 2.80Mb. Hmmm..., don't bother to download it ;), i'm starting to see the cause of my problem. The image is quite big (2100x2800) and when the image is scaled to fit in the screen, the ugly 'bands' appears, but they aren't visible with a 1:1 zoom. I've scaled down the image and the bands are not there now. So it seems the problem is with the zoom. When a big image is fitted to the screen size, it doesn't look nice (you know, bands ;)). What confused me was that gqview, with the same image size, fitted it to the screen size and no bands were drawed... I think now is time for the gimp gurus to solve this zoom thing, i'll leave the image in the URL above some time in case somebody is interested ;) Thanks all for your help ;), cheers, -- David Gómez The question of whether computers can think is just like the question of whether submarines can swim. -- Edsger W. Dijkstra ___ Gimp-developer mailing list [EMAIL PROTECTED] http://lists.xcf.berkeley.edu/mailman/listinfo/gimp-developer
Re: [Gimp-developer] Dithering
Hi Sven ;), The GIMP display canvas uses the dithering routines from GdkRGB which is probably what you are refering to. Yes i was referring to GdkRGB dithering, but it seems that was not the cause of the problem, as i said in my previous mail, and i was wrong thinking that was caused by gimp dithering implementation. Thanks, -- David Gómez The question of whether computers can think is just like the question of whether submarines can swim. -- Edsger W. Dijkstra ___ Gimp-developer mailing list [EMAIL PROTECTED] http://lists.xcf.berkeley.edu/mailman/listinfo/gimp-developer
