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January 2007

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2007.01.19 21:54 "Orientations with rhs are creating problems in tiffcp", by Richard Nolde

Tiffcp contains the code snippet below for dealing with the orientation 
tag. It appears that any image that has an top or bottom right-hand side 
orientation is changed to the corresponding left-hand side when it is 
written out.  However, the data is not read in and rewritten with the 
strip data reversed.  This is causing problems for some old images I 
have run across, producing a mirror effect on the data.  I wrote 
mirroring code in tiffcrop and this could be called to mirror the data, 
there by correcting the problem.  Has anyone else seen this issue?  This 
is particularly nasty for Group3/4 compressed images, but my tiffcrop 
utility can handle them so I think that this would work here too.

Is this worth pursueing or will it break other codecs or parts of the 
code.  I haven't tried a patch yet, but it would appear to me that you 
should not change he orientation unless you also reverse the data that 
it describes.


Richard Nolde

    TIFFGetFieldDefaulted(in, TIFFTAG_ORIENTATION, &orientation);
    switch (orientation) {
        case ORIENTATION_RIGHTBOT:    /* XXX */
            TIFFWarning(TIFFFileName(in), "using bottom-left orientation");
            orientation = ORIENTATION_BOTLEFT;
        /* fall thru... */
        case ORIENTATION_LEFTBOT:    /* XXX */
        case ORIENTATION_RIGHTTOP:    /* XXX */
            TIFFWarning(TIFFFileName(in), "using top-left orientation");
            orientation = ORIENTATION_TOPLEFT;
        /* fall thru... */
        case ORIENTATION_LEFTTOP:    /* XXX */
    TIFFSetField(out, TIFFTAG_ORIENTATION, orientation);