home *** CD-ROM | disk | FTP | other *** search
- Newsgroups: comp.graphics
- Path: sparky!uunet!cis.ohio-state.edu!zaphod.mps.ohio-state.edu!news.acns.nwu.edu!jegog.acns.nwu.edu!user
- From: paulhz@casbah.acns.nwu.edu (Paul Hertz)
- Subject: Re: Your one stop GRAPHICS shop!
- Message-ID: <paulhz-120193093343@jegog.acns.nwu.edu>
- Followup-To: comp.graphics,alt.graphics.pixutils
- Sender: usenet@news.acns.nwu.edu (Usenet on news.acns)
- Nntp-Posting-Host: jegog.acns.nwu.edu
- Organization: Northwestern University
- References: <1993Jan6.150118.24767@a.cs.okstate.edu> <1ifdfaINNim7@hpscit.sc.hp.com> <1ij6taINN8rf@gvgspd.gvg.tek.com> <9301084434@genesis.nred.ma.us>
- Date: Tue, 12 Jan 1993 15:39:39 GMT
- Lines: 54
-
- In article <9301084434@genesis.nred.ma.us>, abh@genesis.nred.ma.us (Andrew
- Hudson) wrote:
-
- > Having worked on a project which samples at 48-bits (16-bit CCD
- > * 3 planes) and then quantizes down to 24-bit I can say that
- > the human eye CAN and does distinguish color information
- > at higher than 24-bit/pixel. This information is especially
- > noticeable in highlights and shading, i.e. dynamic range.
- >
- > When we get tired of those ugly 24-bit images we can get started
- > on 36 and 48-bit images!
- >
- > - Andrew Hudson
- > North Coast Software
-
-
- Part of the apparent ability to distinguish color differences at that pixel
- depth may come from the non-linear response of the eye to specific
- wavelengths and intensities of light. I.e., we see many more shades in
- certain wavelengths and intensities that in others, so there may indeed be
- colors displayed which differ only in least significant bits (as far as
- their internal represeatation is concerned), but which appear clearly
- different to the eye. In any case, color in this sense is a psychological
- phenomenon, rather than a technological or scientific. While gamma settings
- on monitors attempt to approximate the response of the human eye, they are
- *only* an approximation.
-
- Also, re, JPEG compression:
-
- In my experience JPEG does an excellent job with scanned images, where
- there is an overall graininess to the image. JPEG works, so I'm informed,
- by transforming spatial domain information to frequency domain information,
- and then removing or smoothing frequencies which are considered only
- marginally perceptible. This makes the image easier to compress--which is
- subsequently done using *I think--correct me if I've remembered this wrong*
- LZW compression. Differencing an image before and after compression reveals
- that pixel values have been slightly shifted.
-
- However, for images with single pixel lines, flat shaded areas, or geomtric
- patterns, JPEG does not work so well. An RLE compression method (such as
- Apple's PICT), or LZW-TIFF will usually squeeze such files apprecialby,
- without generating the "fringe" artifacts JPEG seems to create.
-
-
- And the thread goes on...
-
-
-
- /\\ | Paul Hertz
- / \\ | Advanced Technology Group, Northwestern University
- / \/ \| 627 Dartmouth Place
- \ /\//| Evanston, IL 60208
- / |
- \\// | Internet: paulhz@casbah.acns.nwu.edu
-