LibTiff Mailing List
TIFF and LibTiff Mailing List Archive
October 2005
Previous Thread
Next Thread
Previous by Thread
Next by Thread
Previous by Date
Next by Date
Contact
The TIFF Mailing List Homepage
This list is run by Frank Warmerdam
Archive maintained by AWare Systems
Thread
2005.10.27 15:55 "Re: How located pixels with BitsPerSample not bound to byte?", by Bob Friesenhahn
> If we talking about testing exotic images. > > Look at the flower-rgb-contig-12.tif from the test images. > It have RGB,Uncompressed, PlanarConfig=Continue, and > BitsPerSample=12 > > How the pixels are located inside a strip in such case? > I really cann't understand :) > > Is it correct? > > Bytes: 0 | 1 | 2 | 3 | 4 > Bits : 76543210|7654|3210|76543210|76543210|7654|3210 > Pixels: rrrrrrrr|rrrr|gggg|gggggggg|bbbbbbbb|bbbb|rrrr| > Samples: hiR |lowR|hiG | lowG | hiB |lowB| hiR I think that this is correct. There is some code from GraphicsMagick which helps read/write samples from "bit streams". The code can be obtained via the web from "http://cvs.graphicsmagick.org/cgi-bin/cvsweb.cgi/GraphicsMagick/magick/bit_stream.h". The code is quite easy to use ('bytes' is a stream of bits such as a scanline): BitStreamReadHandle bit_stream; BitStreamInitializeRead(&bit_stream, bytes); Loop around code like this to collect all samples ... unsigned int red = BitStreamMSBRead(&bit_stream, 12); unsigned int green = BitStreamMSBRead(&bit_stream, 12); unsigned int blue = BitStreamMSBRead(&bit_stream, 12); There is similar code to support writing bit streams. The performance may not be as good as carefully hand-crafted code for a specific depth, but it makes dealing with depths ranging from 1 to 32 bits very easy. Since the code is inlined, if you can fill an array with red, green, blue and only invoke BitStreamMSBRead() once in the sample extraction loop (tighter loop), performance is likely to be better. Bob ====================================== Bob Friesenhahn bfriesen@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/ GraphicsMagick Maintainer, http://www.GraphicsMagick.org/