LibTiff Mailing List

We're using LeadTools (version 10.0) for JPEG TIFF writing, and I've noticed
a few things that don't seem right.

Saving an 8 bit gray JPEG into a TIFF, I get a TIFF with compression=7, but
it includes the tags JPEGProc, JPEGInterchangeFormat,
JPEGInterchangeFormatLength, JPEGRestartInterval, JPEGLosslessPredictors and
JPEGPointTransforms, and has the single tile pointing part way into the
interchange format. My reading of TIFF Tech Note 2 is that the only valid
tag for compression=7 is JPEGTables.
It looks very much to me like this is a JPEG 6 compressed TIFF with the
compression incorrectly set to 7, which violates both the TIFF 6.0 spec and
the tech note.
Changing the compression back to 6 undoes the damage and returns the TIFF to
about as readable as you get using JPEG 6.

In addition, the JPEGInterchangeFormat points to a JPEG stream that fails to
contain an EOI marker. According to my reading of the TIFF 6.0 spec and JPEG
spec, it must contain one.
This could seriously complicate general TIFF copiers because some software
(e.g. Wang/Kodak Imaging) writes the wrong value into
JPEGInterchangeFormatLength. In order to rewrite a JPEG 6 compressed TIFF
containing JPEGInterchangeFormat, you need the correct length. That can be
fixed by finding the JPEG EOI marker from the start of the
JPEGInterchangeFormat. But now, because LeadTools is missing off the EOI
marker, the only safe way to find the correct length of the
JPEGInterchangeFormat is to actually parse the JPEG data, variable length
codes and all, until the end is reached. Or the copier has to
decompress/recompress the image.

Does what I've said sound right? Does anyone that knows a bit more want me
to send them an image to confirm it?

Thanks,

Brent Foster


AWARE [SYSTEMS]		Imaging expertise for the Delphi developer
		TIFF and LibTiff Mailing List Archive
	LibTiff Mailing List TIFF and LibTiff Mailing List Archive May 2000 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 2000.05.17 02:40 "LeadTools bad JPEG 7 TIFF compression?", by Brent Foster 2000.05.17 03:02 "More LeadTools JPEG 7 TIFF compression problems?", by Brent Foster 2000.05.17 22:20 "Re: LeadTools bad JPEG 7 TIFF compression?", by Tom Lane 2000.05.17 02:40 "LeadTools bad JPEG 7 TIFF compression?", by Brent Foster We're using LeadTools (version 10.0) for JPEG TIFF writing, and I've noticed a few things that don't seem right. Saving an 8 bit gray JPEG into a TIFF, I get a TIFF with compression=7, but it includes the tags JPEGProc, JPEGInterchangeFormat, JPEGInterchangeFormatLength, JPEGRestartInterval, JPEGLosslessPredictors and JPEGPointTransforms, and has the single tile pointing part way into the interchange format. My reading of TIFF Tech Note 2 is that the only valid tag for compression=7 is JPEGTables. It looks very much to me like this is a JPEG 6 compressed TIFF with the compression incorrectly set to 7, which violates both the TIFF 6.0 spec and the tech note. Changing the compression back to 6 undoes the damage and returns the TIFF to about as readable as you get using JPEG 6. In addition, the JPEGInterchangeFormat points to a JPEG stream that fails to contain an EOI marker. According to my reading of the TIFF 6.0 spec and JPEG spec, it must contain one. This could seriously complicate general TIFF copiers because some software (e.g. Wang/Kodak Imaging) writes the wrong value into JPEGInterchangeFormatLength. In order to rewrite a JPEG 6 compressed TIFF containing JPEGInterchangeFormat, you need the correct length. That can be fixed by finding the JPEG EOI marker from the start of the JPEGInterchangeFormat. But now, because LeadTools is missing off the EOI marker, the only safe way to find the correct length of the JPEGInterchangeFormat is to actually parse the JPEG data, variable length codes and all, until the end is reached. Or the copier has to decompress/recompress the image. Does what I've said sound right? Does anyone that knows a bit more want me to send them an image to confirm it? Thanks, Brent Foster

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2000.05.17 02:40 "LeadTools bad JPEG 7 TIFF compression?", by Brent Foster