cs472222@umbc5.umbc.edu (CMSC 472/201) (12/23/89)
Mr. Wicks,
You're wrong wrong wrong about amiga graphics modes (although I
wish you were right.) The following are the supported modes on the
standard denise: (Please, someone ELSE please correct ME if I'm wrong).
320 x 200 32 colors/4096 colors
320 x 400 32 colors/4096 colors interlaced
320 x 200 64 colors/4096 colors extra_halfbrite
320 x 400 64 colors/4096 colors interlaced extra_halfbrite
320 x 200 4096 colors/4096 colors HAM
320 x 400 4096 colors/4096 colors interlaced HAM
640 x 200 16 colors/4096 colors hires
640 x 400 16 colors/4096 colors interlaced hires
Any of these modes may be overscanned.
The ECS supposedly supports the following additional modes:
640 x 480 4 colors/64 colors productivity mode (Multisyncs)
640 x 960 4 colors/64 colors interlaced productivity mode
1280 x 200 4 colors/64 colors super hires
1280 x 400 4 colors/64 colors interlaced superhires
1280 x 480 1 color/64 colors ???????????
1280 x 960 1 color/64 colors ???????????
My question is, why the limitation of color selection to 64 colors?
Is it possible that a future denise may incorporate more
bitplanes/colors?
Why not go straight to that denise?
Larry Augsburger
BITNET: CS472222@UMBC5.UMBC.EDU
CS379240@UMBC1.UMBC.EDU
jms@tardis.Tymnet.COM (Joe Smith) (01/08/90)
In article <2651@umbc3.UMBC.EDU> cs472222@umbc5.umbc.edu (CMSC 472/201) writes: >My question is, why the limitation of color selection to 64 colors? >Is it possible that a future denise may incorporate more bitplanes/colors? How to get 1280x400 resolution (in 4 shades of gray) on all existing Amigas: In addition to the standard sync and analog RGB signals on the DB23 connector, there are 4 digital signals for IBM CGA-compatible RGBI monitors. These bits are driven by 4 of the 12 bits of the currently displayed color; R3, G3, B3, and B0. If the color palette is carefully chosen, each of the 4 output bits can be controlled by a single bit plane. That is; changes to bit plane 1 affect only the R bit, bit plane 2 only the G bit, etc. A piece of external hardware could be designed to look at those 4 bits, two at time. Instead of looking at 4 bits in parallel to display a single pixel in one of 16 colors, this hardware would display two pixels, each one being one of 4 shades of gray. This means a 640x400x4-bitplane image would show up as a 1280x400x4-gray image. Note that this would work on all Amigas, including the A1000, since all the fancy hardware is external. However, a new graphics.library would be needed since adjacent pixels on the screen are no longer adjacent bits in the same word, but rather in different bit planes. This is how I had assumed the Hedley Monitor worked when I was first announced. That assumption turned out to be wrong, but the ideas presented above are still valid. Now, for color. The video slot on the American A2000 has all 12 color bits available. A device plugged into this slot could to the same trick to look at half of the bits (2 red, 2 green, and 2 blue), then the other 6 bits. The end result is that the half-width pixels can be any one of 64 colors. As in the monochrome setup above, 4 bitplanes are combined to act as 2 independent virtual bitplanes. The end result is a 1280x400 screen that displays 4 colors out of a palette of 64. Of course this requires interlaced video for a 400-line tall screen, since it is still running at NTSC frequences. Noninterlaced screens are limited to 200 to 243 lines. If the horizontal sync pulse (and horizontal blanking signal) were to be made one half its width, and a second h-sync pulse added in the middle of the line, it would split this new 1280 pixel line into two 640 pixel lines, running at a horizontal frequency of 31.4 KHz instead of 15.7 KHz. At this point, the Amiga's hardware thinks it is displaying a 640x200x16-color screen, but the additional hardware converts this to a 640x400x4-color noninterlaced screen on a VGA or multisync type monitor. Now you can see why I was not at all surprised when Commodore announced that the "Productivity Mode" of the ECS chips will be 640x400, noninterlaced, showing 4 colors out of a palette of 64 colors. -- Joe Smith (408)922-6220 | SMTP: JMS@F74.TYMNET.COM or jms@gemini.tymnet.com BT Tymnet Tech Services | UUCP: ...!{ames,pyramid}!oliveb!tymix!tardis!jms PO Box 49019, MS-D21 | PDP-10 support: My car's license plate is "POPJ P," San Jose, CA 95161-9019 | humorous dislaimer: "My Amiga speaks for me."