carltons@girtab.usc.edu (Carlton Szeto) (10/02/90)
Concerning all these great vga screens now pretty much standard on todays laptops, are there any shade mapping problems associated with their limited number of shades. I seem recall that vga will display 256 colors, so if the screens on these laptops can display only show 16, wouldn't there be certain combinations of shades where if they happen to map to the same shade on the LCD screen, seem to be one color and cause viewing problems? What about the new Zeos laptop that displays 32 shades. -Carl -- -jackal :)
bryan%cirrusl@oliveb.ATC.olivetti.com (Bryan Richter) (10/02/90)
In <12285@chaph.usc.edu> carltons@girtab.usc.edu (Carlton Szeto) writes: >Concerning all these great vga screens now pretty much standard on todays >laptops, are there any shade mapping problems associated with their limited >number of shades. I seem recall that vga will display 256 colors, so if the >screens on these laptops can display only show 16, wouldn't there be certain >combinations of shades where if they happen to map to the same shade on the LCD >screen, seem to be one color and cause viewing problems? This is somewhat dependent on the VGA controller used to drive the display. There are several ways that you can choose to map the 256K colors it is possible to display with the standard VGA RAMDAC (Inmos 171 or Bt476, etc). The algorithm that the Cirrus Logic GD610/620 (the controller in the Zeos laptop) does a weighted sum of the RGB values written to the RAMDAC (x*R+y*G+Z*B). In a standard 16 color mode the 4 MSB's of the result defines which of the 16 gray shades will be displayed. This will definitely result in the ability to have many shades map into one grayshade. However, since it tends to map the intensity of the color image into an appropriate intensity monochrome image, most images will look fine. Of course, some images will look better than others. You should also know that IBM markets a monochrome VGA monitor. It can display 64 shades of gray. Some of the early VGA LCD controllers had other algorithms that didn't look as good to me (some bias here). >What about the new Zeos laptop that displays 32 shades. The GD610/620 is able to display 32 shades of gray in mode13 with a dithering algorithm (this looks really good to me - more bias here). In other modes, the chipset displays 16 shades of gray and that is the maximum number of shades for VGA anyway. --bryan disclaimer: I speak only for me. >-Carl >-- >-jackal :)