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August 2008
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2008.08.11 13:18 "Custom fields and BIGTIFF (was: Writing custom fields with big counts)", by Edward Lam
Hi, Tom brings up an issue regardless with _TIFFField's field_readcount and field_writecount though. What's the reason for still keeping them 16-bit in libtiff 4.0? Joris? Is there a TODO item still to deal with these? It strikes me that now might be a good time to switch them to 64-bit? -Edward Tom Harris wrote: > I am writing my custom tag as described on the docs page "Adding NewTags". > > What I have found is that if your count is greater than 32767, the > field_readcount and the field_writecount members of the TIFFFieldInfo > struct must be set to TIFF_VARIABLE2 (-3), not TIFF_VARIABLE (-1). > This forces 32 bit access, rather than 16 bit access. > > Someone with commit rights to the docs might care to update the passage: > > ``The special value TIFF_VARIABLE2 (-3) is presumably similar to > TIFF_VARIABLE though I am not sure what the distinction in behaviour > is. This field is TIFF_VARIABLE for variable length ascii fields.'' > > To: > > ``If a variable number of values are to be read (such as for variable > length ascii fields), then this field is set to TIFF_VARIABLE. > However, if the count is to be greater than 32767, then the field must > be set to TIFF_VARIABLE2 to force 32 bit access.'' > > Regards > > Tom Harris <celephicus@gmail.com>