Re: Vis EG colour depth
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On Fri, 1 Aug 2003, Daron Edie wrote:
> why only 8 bit colour depth? I did a search on the news group archives
> and discovered that is all the card is capable of but was it a design
> decision on HP's part?
That's right. In the early 1990's when HP was developing the 712 model as
a cheap entry level desktop engineering workstation, video RAM was fairly
expensive, and 24bit color was considered only for high end machines. The
commodity PC market was still sitting at 8 or 16 bpp. To allow reasonable
color reproduction with only an 8 bit frame buffer, HP implemented a
process called "color recovery," essentially hardware color dithering and
lowpass filtering of the chroma signal to a 1280x1024@72Hz screen so that
an 8bpp framebuffer could as good as a 24bpp framebuffer. HP patented the
"color recovery" process, and never released the design of the Visualize
chipset so that non-HP-UX operating systems could use the hardware
acceleration and color dithering. If you want good color on your HP
Visualize-EG, you need to run HP-UX and HP-UX's X server, and have your
applications make specific calls to the HP X server to activate "color
recovery". With Debian Linux/XFree86, you get an 8-bit, undithered
framebuffer, and no hardware acceleration for even simple stuff like
window drags, either!
Descriptions of the hardware and algorithms were published in the mid
1990's once the hardware was shipping. A description of the model 712
graphics hardware was published in
Paul Martin, "An integrated graphics accelerator for a low-cost
multimedia workstation," Hewlett-Packard Journal, April 1995, p. 43.
The "color recovery" process was described in
Anthony Barkans, "Color recovery: true-color 8-bit interactive
graphics", IEEE Computer Graphics and Applications, Jan/Feb 1997, p. 67.
Our research group (imaging radar) was solely a HP shop up until a few
years ago, mainly due to the floating point performance of the Precision
Architecture (PA). Since all radar imaging is pseudo-color anyway, the
Visualize-EG graphics cards were fine for desktop use. A few years ago we
got some IA32 machines, and 24bit color suddenly became available. In the
computer lab, we have a choice of IA32 machines with 24bpp color and
fairly slow FPU performance, or PA2.0 machines with 8bpp color and good
FPU performance. Students always choose the IA32 machines. For the PA2.0
machines, which are running a mixture of HP-UX 11 and Debian 3.0, they
prefer HP-UX, as the desktop is more responsive due to the use of hardware
2D graphics acceleration.
- --
Leif Harcke
lharcke@stanford.edu
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