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September 2006

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2006.09.13 14:05 "Image data alternation and bug 438", by Felix Wehrmann

Hello list

I use libtiff via the open-source library FreeImage. In particular, I
store 16bit greyscale image data in a multi-paged TIFF file.

I realised that the data of an image, appended to a multipage TIFF file,
gets
altered by libtiff. Changes take probably place in TIFFWriteScanline,
where a call to 'postdecode' does some transformation of the data. I
assume further that FreeImage is not involved actively in this part
since it only passes down data pointers.

Is there any way to continue using the data pointer after storing the
image, i.e. avoiding any changes of the data it points at?

What controls the postdecode function call - is data always altered?
Maybe I am doing things wrong here and unintentionally trigger some form
of conversion.

I also found some discussion about little/big endian and bug 438 in
connection with this issue. 

Any ideas are very much appreciated.

Thanks
Felix

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