Subject: [PNG] WANTED: 16-bit grayscale and 48-bit true-color images

From: roe2 at ellis.uchicago.edu (Cave Newt)
Date: Mon, 13 Feb 1995 05:37:10 GMT

The PNG group is busy testing various combinations of filters, interlacing
and compression, but we really could use some real-world images with 16-bit-
per-sample color depth (grayscale and RGB; images with alpha channel are OK,
too).  So far our test corpus has a good number of regular 24-bit true-color
and 8-bit (or less) color-mapped images, but we need some with 16 bits per
color.  (We have considered creating 16bps images out of 8bps ones, but they
would be extremely small and not necessarily representative of real 16bps
images).  Some 12-bit medical images would be nice, too.

If you either (1) have some, (2) have some way to generate them, or (3) have
a pointer to some somewhere on the net, please send me e-mail with details
(assuming you're willing to donate a few for testing purposes only).  We can
probably deal with most reasonable formats.  (PGM/PPM would have been pref-
erable if they supported 16bps in binary mode, but they don't.  Oh well.)

Btw, for those in s.a.f and s.m.* who don't know what PNG is:  it stands for
"Portable Network Graphics" (or, unofficially, "PNG's Not GIF") and will be 
a lossless replacement for the GIF format with support for up to 16-bit color
depth.  The compression method is deflation, the same as in Zip/PKZIP and 
gzip.  (Completely mindless tests of color-mapped images with LZW [GIF] vs.
deflation shows 10% improvement in compression even without any special fil-
ters.  I don't have any numbers to compare with lossless JPEG.)

Note follow-ups.

Greg Roelofs
Info-ZIP and PNG group

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From: tg3 at u.washington.edu (Thurman Gillespy III)
Date: Tue, 14 Feb 1995 17:29:55 -0800

> ters.  I don't have any numbers to compare with lossless JPEG.)

16 bit (12 bit) radiologic image are available by anonymous ftp at:

   wuerlim.wustl.edu/pub/dicom/images/version3

They are in DICOM format. But you can just bypass the header by calculating
the image dimensions (eg, header = filesize - (xdim * ydim * 2)). Byte order
is little endian.

CTs are 512x512, MRIs are 256x256. I wouldn't mess with the CR (computed
radiography) or digitized radiograpbs unless you need to work with very large
images.
-- 
Thurman Gillespy III             |  tg3 at u.washington.edu
Department of Radiology, SB-05   |  voice (206)543-3320
University of Washington         |  fax   (206)543-6317
Seattle, WA 98195                |