Path: utzoo!utgpu!watmath!att!tut.cis.ohio-state.edu!cica!gatech!ncar!stout!cook From: cook@stout.ucar.edu (Forrest Cook) Newsgroups: sci.electronics Subject: Re: sync signal generator Message-ID: <3983@ncar.ucar.edu> Date: 14 Aug 89 23:34:17 GMT References: <89216.120136BHB3@PSUVM> <17660014@hpfcdj.HP.COM> Sender: news@ncar.ucar.edu Reply-To: cook@stout.UCAR.EDU (Forrest Cook) Organization: Field Observing Facility, NCAR, Boulder, CO Lines: 47 In article <17660014@hpfcdj.HP.COM> myers@hpfcdj.HP.COM (Bob Myers) writes: >>We just rolled in a couple of Ardent workstations that provide 1280 X 1024 >>X 16,777,216 color resolution. >I'm a little uncertain as to what you mean by "color resolution". The number >you give for the Ardent workstation mentioned could be misleading if expressed >in this manner, as a display with 1280x1024 pixels can't possibly display >16 million colors *simultaneously*. Ardent calls their 24 bit color table "Truecolor" and I was just wondering if it was possible to see the finest steps in a smooth transition on the monitor. While you can only display 1310720 unique colors at a time on the screen, it would be possible to make a 16 frame "movie" loop that displayed all of the possible colors. A possible test would be to have R increase with X, G increase with Y, and B increase with time/frame #. >Assuming that the video amplifiers in your >monitor are up to snuff, and the dot pitch of the CRT was properly chosen, >the monitor is in fact capable of displaying 1280x1024 pixels, each a >different color. Age should not affect this unless the amplifiers degrade >or there is damage to the CRT, especially in the shadow mask. I was referring to the aging of the Cathode on the CRT. Some of our Ramtek monitors are approaching 10 years of on time and their colors have changed intensities over the years. An old color table that we designed to have 17 discrete colors looks ok on a new crt but some of the color differences are hard to notice on an old CRT. This is after both monitors have been set up with a Black->Red, Black->Green, Black->Blue and Black->white test pattern. If you draw one of these primary color bars with 256 levels and adjust the monitor so that it is black on one side and saturated on the other, the color change will not appear to be linear. It will be different from an old monitor to a new monitor. It will also differ between the red, green, and blue phosphors. It will be very different on a video photograph. The individual's eyes and the ambient lighting will also play a role. All of these parts have non-linear response curves. Ardent was clever enough to put what they call "Gamma Correction Tables" in between their color table and each video DAC to allow for correcting the curves. I have not discovered how they determine the curves, but it sounds like they can be changed fairly easily. These promise to be very useful in correcting for video photography. Now, if I can only figure out how to generate the curves :-) ^ ^ Forrest Cook - Beware of programmers who carry screwdrivers - LB /|\ /|\ cook@stout.ucar.edu (The preceeding was all my OPINION) /|\ /|\ {husc6|rutgers|ames|gatech}!ncar!stout!cook /|\ /|\ {uunet|ucbvax|allegra|cbosgd}!nbires!ncar!stout!cook