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June 2009
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2009.06.14 23:48 "Re: Tiff 16 bit and 32 bit images", by Bob Friesenhahn
On Sun, 14 Jun 2009, Keshab Neupane wrote: > Hi All, Can you please look at my code and check what am I doing > wrong. I have to copy data from tiff 16 bit image into buffer and > then into destination buffer. If you plan for your support of TIFF sample depths to be limited, then it seems easier for you to allocate 'buffer' as a uint16 type and add a necessary cast to (char *) only when passing a pointer to TIFFReadScanline(). Depending on how you use the data, this may offer performance benefits as well. The problem you are running into is with basic C programming and not libtiff related. The more complex your solution looks, the more likely it is to be wrong. > Here, photometric interpretation is min-is-black, what will happen > if I have RGB or greyscale image i.e how do I copy data from buffer > to destination ? If the image has only gray samples then it is organized as just gray samples. If it is RGB, it is usually ordered RGBRGBRGB except for in the case of planar TIFF, in which case you need to specifically request the red, green, or blue planes and they look like the gray case. If you need to deal with TIFF with an alpha channel, or extra samples, then there may be additional samples sandwiched between the RGB samples (e.g. RGBA). It is also possible for extra samples to be included with grayscale files. > Sometimes, SAMPLEFORMAT is not given/available, how I can decide > what data types are tiff image made from. I need to handle 16 bit > signed/unsigned and 32 bit float values !! If sample format is not defined, then it must be unsigned integer data. This should not be a problem for your code since you can retrieve the tags via TIFFGetFieldDefaulted() and libtiff will supply the default if the file does not supply a value. > Any nice books where I can read all about tiff image format ? What > are the possible tiff image formats available/theoretically possible > ? I googled it but couldn't find any satisfactory result ? The Encyclopedia of Graphic File Formats provides a nice overview. Unfortunately, the book is out of print but it is online here: http://www.fileformat.info/format/tiff/egff.htm Otherwise there is the TIFF specification itself, and several Adobe application notes. As far as what is available/theoretically possible, you may be astonished at what TIFF is capable of. I generated some integer and float TIFF sample files using GraphicsMagick and made them available at: ftp://ftp.graphicsmagick.org/pub/outgoing/tiff-sample-images.tar.gz ftp://ftp.graphicsmagick.org/pub/outgoing/bigtiff-sample-images.tar.gz They are intended to be used by software developers. This is just to start since these files are all uncompressed and only represent one endian order, one bit order, and don't include any extra samples such as an alpha channel. Bob -- Bob Friesenhahn bfriesen@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/ GraphicsMagick Maintainer, http://www.GraphicsMagick.org/