2008.01.10 23:04 "Re: [Tiff] LibTiff..Reading partial strips", by Nikhil Shirahatti
Also, I may only want to read the first N pixels ..lets say the interesting data was in the first N pixels ..then why read the remaining? If the ReadStrip is done several times(lets say 10000 rows) then each time we end up reading M pixels (M >> N) rather than N..and this does cause a performance hit..
On Jan 10, 2008 2:48 PM, Nikhil Shirahatti <firstname.lastname@example.org> wrote:
ReadScanline doesn't really help me..OK let me rephrase the question...the reason I want to read partial strips is:
lets say a strip is of length 1000. I want to read be able to read the strip from 0 to 100, 101 to 200...and so on so I have 10 chunks of data.
The reason why I want to do this is to convert it to our internal structure for further processing. One may argue why not use the tiles in libtiff...because we are not guaranteed that the tiff is tiled (they may be from anywhere)...Unfortunately the scan line also reads the whole scan line...even though much less memory intensive doesn't serve our goal...
On Jan 10, 2008 2:08 PM, Frank Warmerdam <email@example.com> wrote:
I havent tried it..but the cautionary note that " It is not always possible to do so due to decompression constraints" scares me. I also
> > > read on the archive that "that *strip* * chopping* only works for
uncompressed IFDs.". How common(or uncommon) is this? When would one use compressed IFD's?
The tiff's we get can be compressed or uncompressed formats and we
> > have
support them all. :)
I think Bob means compressed images. There is no such thing as compressed IFDs. Compressed TIFF images are quite a common case, and fax compressed images are often one strip.
In addition to "strip chopping", libtiff also has the TIFFReadScanline() function for reading strips one scanline at a time. This operates without needing to read and decompress the whole strip at once.
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Nikhil V Shirahatti