JPEG2000 and grayscale image size growth

[John Faughnan]

I did some initial testing using the most extreme (low quality) JPEG
2000 image compression settings with Distiller 6. (JPEG2000 is new in
Acrobat 6. A primary potential application is scanning color documents
including maps.)

I first scanned a sample document at 200x200 16 bit color, producing a
10MB tiff (lzw compressed) file. The JPEG 2000 PDF of this image was
only 160K. The text in the 160K file was quite readable. I considered
this to be a very good result, almost a 70 fold compression with
preserved text readability. In my past experience JPEG compression of
a scanned text image makes the text unreadable due to jpeg artifact
even with moderate (10 fold) compression. This is a qualitative
improvement over JPEG. (For reference, past experience using B/W
images scanned with CCITT 4 compression produces typically a 40K image
of the same test document.)

I then scanned the same document at 200x200 gray scale. This resulted
in a 3.6MB TIFF (lossless compression). The JPEG2000 compressed PDF,
however, was 1.77MB! A JPEG PDF of the same file was only 300K (and
was quite readable). Something's wrong here - I expected a JPEG2000
maximally compessed PDF of this grayscale image to come in at about
60-80K. I suspect a bug in Distiller's handling of JPEG2000 compressed
grayscale images. I wonder if Distiller is not honoring the
compression setting for grayscale images.

Has anyone seen anything like this?

john
[email]jfaughnan@spamcop.net[/email]

meta: jfaughnan, jgfaughnan, jpeg2000, jpeg 2000, pdf, jp2k, lossy
compression, scans, scanner, scanned image, acrobat, adobe acrobat 6,
text

[John Faughnan]

[email]jfaughnan@spamcop.net[/email] (John Faughnan) wrote in message news:<5c0dbfb4.0404081405.1e8f3bd@posting.google.c om>...

> I did some initial testing using the most extreme (low quality) JPEG
> 2000 image compression settings with Distiller 6....
> I then scanned the same document at 200x200 gray scale. This resulted
> in a 3.6MB TIFF (lossless compression). The JPEG2000 compressed PDF,
> however, was 1.77MB! A JPEG PDF of the same file was only 300K...

Thinking about this a bit more, I suspect Acrobat is using CCITT 4.0
on this gray scale TIFF rather than JPEG 2000. In other words, it is
miscategorizing the image as black and white rather than grayscale.
JPEG 2000 is not available as a Distiller option for black and white
images.

I don't know how Distiller "decides" that a printed image is b&W,
color, or gray scale. The method I was using produces the TIFF from
the scanner, then "prints" it to the Distiller printer. It may be that
the print stream headers are not interpreted correctly by Distiller.
If I have time, I'll retest with other methods of image acquisition.

john
[email]jfaughnan@spamcop.net[/email]

meta: jfaughnan, jgfaughnan, jpeg2000, jpeg 2000, pdf, jp2k, lossy
compression, scans, scanner, scanned image, acrobat, adobe acrobat 6,
text