vuescan tiff compression not working

[Victor H]

Hi,
I'm using the trial version of vuescan 8.1.19 under Suse 9.2 Linux.
Doing a scan of a 1200*1200 pixel area, which needs theoretically 4.320.000
bytes in 24bit RGB mode and 8.640.000 bytes in 48bit RGB mode.
Saving as Tiff file with :
- 24 bit, compression off gives 4.321.324 bytes ok.
- 24 bit, compression on gives 2.753.210 bytes ok.
- 48 bit, compression off gives 8.642.652 bytes ok.
- 48 bit, compression on gives 9.732.974 bytes n o t ok.
Why is the compressed file larger than the uncompressed one?

afaik vuescan 7.5.x did not have this problem.

Any idea?

 

[Preston Earle]

I believe this TIFF compression is LZW. (You can read more than you want
to know about LZW compression at
http://www.dogma.net/markn/articles/lzw/lzw.htm). The short answer is
that LZW does not handle 16-bit (48-bit) files at all well. The
"compressed" file is often larger than the uncompressed one.

Preston Earle
PEarle at triad dot rr dot com

 

[Victor H]

I believe this TIFF compression is LZW. (You can read more than you want
to know about LZW compression at
http://www.dogma.net/markn/articles/lzw/lzw.htm).

Thank you for this hint.

The short answer is
that LZW does not handle 16-bit (48-bit) files at all well. The
"compressed" file is often larger than the uncompressed one.

But how can we explain that it does work well in earlier vuescan versions?

Victor