[Image-SIG] Re: silent corruption of FillOrder: lsb-to-msb TIFF reads?
Fredrik Lundh
fredrik@pythonware.com
Mon, 19 May 2003 17:02:20 +0200
Jeff wrote:
> Looking at the output, I suspect that PIL's TIFF reader
> is ignoring the FillOrder tag. Even more suspicious, when I
> convert the TIFF to FillOrder: msb-to-lsb, no such corruption
> occurs.
> TIFF Directory at offset 0x5c4e9ee
> Image Width: 4913 Image Length: 6567
> Resolution: 600, 600 pixels/inch
> Bits/Sample: 8
> Compression Scheme: None
> Photometric Interpretation: RGB color
> FillOrder: lsb-to-msb
> Orientation: row 0 top, col 0 lhs
> Samples/Pixel: 3
footnote: the TIFF 6.0 specification says:
We recommend that FillOrder=2 [lsb-to-msb] be used only in special-
purpose applications. It is easy and inexpensive for writers to reverse
bit order by using a 256-byte lookup table. FillOrder = 2 should be
used only when BitsPerSample = 1 and the data is either uncompressed
or compressed using CCITT 1D or 2D compression, to avoid potentially
ambigous situations.
Support for FillOrder=2 is not required in a Baseline TIFF compliant
reader.
so this file is pushing the envelope somewhat...
</F>