LibTiff Mailing List
TIFF and LibTiff Mailing List Archive
June 2012
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
2012.06.18 13:15 "Re: Tiff Digest, Vol 97, Issue 5", by Olivier Paquet
On Sun, Jun 17, 2012 at 3:47 PM, He Yang <he-yang@live.com> wrote: > I am trying to set the EXIFTAG_EXPOSURETIME, which is a > TIFF_RATIONAL, is there are way to make sure the forward /backward > conversion are always consistent. Does libtiff provide a way to make > sure the rational to float and float to rational, But from my tracing, > I found the precision was lost during read back from the disk file not > from the memory? Not that I know as libtiff stores these as floats (or doubles, I'm not sure) internally and uses a basic conversion method in TIFFWriteDirectoryTagCheckedRational() to write them out as rationals. I think this is where the precision is lost. However, that function could certainly be improved to handle the "1 / x" case with better accuracy as it currently writes out all values < 1 as "x / UINT_MAX". It should be possible to also try "1 / x" and pick the representation with the lowest error. Can you compile your own libtiff to try it if I find some time to write this? Olivier