[poppler] Request for comment: How inconsistent metrics of the image object should be dealt?

[suzuki toshiya]

Hi all,

Now I'm drafting the patch to emit the images coded by CCITT
via CairoOutputDev without reencoding it. From the surface
independence and portability, I think using TIFF is good to
pass CCITT image to Cairo. When I encapsulate CCITT bitstream
into TIFF format, I need to put the metrics infos (CCITT
bitstream itself does not have it, TIFF must have it). There
are 2 different metrics infos may exist in PDF (Width/Height
in Image dictionary and Columns/Rows in DecodeParms dictionary).
There is a possibility that these properties are inconsistent.
I'm not sure how I should deal such case.

I did a small experiments with some data with inconsistent
metrics, and I found that popular PDF browsers show different
behaviours for such cases. Thus I think the inconsistent metrics
should cause some errors. My experiment is summarized at

http://gyvern.ipc.hiroshima-u.ac.jp/~mpsuzuki/pdf-tech/ImagesWithIncorrectMetrics.html

If you have a comment how inconsistent metrics should be dealt,
please let me know.

Regards,
mpsuzuki