Colors on the Amiga

[evil_nerd]

Hello,

I am wondering how much colors a Amiga 500 can display. I have read 16, 32, 64, 4096, but I don't understand. There's a pallat of 4096 colors isn't it? Depending on the mode you can have 16, 32 or 64 colors. But in most Amiga games I see much more colors, very nice indeed, but how do they do that? Is there some trick or something? It wouldn't be logic if the Amiga is limited to 64 colors, because a MSX2 (a few years earlier) could display 512 colors!!! So, can anybody explain this???

[Thomas]

I gave you an answer on The Amiga Forums: http://www.amigaforums.org/forums/viewtopic.php?t=1404

Bye,
Thomas

[evil_nerd]

Yes but its always nice to ask it on a forum where are more people around  :lol:  :-P  :-D  :laughing:  ;-)

But what I ask is is there a trick or something? The games that I've seen have more than 32 colors (some are on the PC VGA (256 colors))

[Khephren]

Thomas's reply was bang on. If a bit technical  
The amiga A500 hardware could display 16 or 32 colours in game. The copper could be used to change colours per line for all those lovely fades you see in amiga games It also had a 4096 HAM mode (mainly for static imagery- Art programs, adventure games, loading screens etc). You could also have different colour/resolution screens dragged up for menu bars etc. I used have a ham hires mod player that looked like a stereo- it used to sit at the bottom of a 16 clour lo-res workbench

The the A500+ and A600 EHB mode was added allowing 64 colours (darker versions of the first 32 colours)

This is all in hardware: coders produced their own code for introducing more colours: Lion heart had hundreds of colours on screen, as did Universe (256 from 4096) rumour has it they picked certain ham colours that caused no fringing, and just diplayed them.

-EDIT- Iv'e just realised mine sounds technical as well, guess there is no easy way to explain it

[Piru]

@Khephren

The the A500+ and A600 EHB mode was added allowing 64 colours (darker versions of the first 32 colours)

All A500 models had EHB.

Only very early A1000 models didn't have it (or was it some early Amiga prototypes, can't remember).

[evil_nerd]

Thomas's reply was bang on. If a bit technical
The amiga A500 hardware could display 16 or 32 colours in game. The copper could be used to change colours per line for all those lovely fades you see in amiga games

so you can change the pallet per line of pixels or something?

It also had a 4096 HAM mode (mainly for static imagery- Art programs, adventure games, loading screens etc). You could also have different colour/resolution screens dragged up for menu bars etc. I used have a ham hires mod player that looked like a stereo- it used to sit at the bottom of a 16 clour lo-res workbench

The the A500+ and A600 EHB mode was added allowing 64 colours (darker versions of the first 32 colours)

This is all in hardware: coders produced their own code for introducing more colours: Lion heart had hundreds of colours on screen, as did Universe (256 from 4096) rumour has it they picked certain ham colours that caused no fringing, and just diplayed them.

fringing? whats that? Whats HAM? 16 or 32 color?

[xeron]

so you can change the pallet per line of pixels or something?

Yes. Actually, you can even change the palette in the middle of a line if you like, all without the main CPU having to do the work.

fringing? whats that? Whats HAM? 16 or 32 color?
HAM is a special display mode.

Normally, the colours on the Amiga display are stored in standard bitplanes. See here for a good description of planar graphics.

HAM is a different way of interpreting the bitplane data, such that some pixels depend on the colour of the pixel to the left of them. If you change that pixel, all the pixels to the right that use this encoding change to the wrong colour, which is known as "fringing". Theres a good description of HAM here.

Edit: Although I'm pretty sure that article is wrong in one respect. I think HAM uses all 6 bitplanes, and uses 2 of those bitplanes to mean "Indexed colour", "Modify Red", "Modify Green" and "Modify Blue"

[Thomas]

HAM is 4096 color. 16 colors can be choosen directly and the others need three pixels to be set (one for changing red, one for changing green and one to change blue).

And yes, theoretically the Copper is able to change the colors every line. But every copper instruction needs as much time as the graphics needs to display four pixels. Changing all 32 color registers needs more time than the horizontal sync signal (the time the beam needs from the right end of one row to return to the outer left in order to start the next row). But it is easily possible to create a color fade from the top to the bottom of the screen with only one color register. For example for creating a sunset sky and the corresponding horizon and ground as a background. No graphics data is needed for this apart from the Copper's command list. The foreground can be painted using the remaining 31 colors (or 4096 colors in HAM).

Bye,
Thomas

[evil_nerd]

Ok, its a little bit more clear for me now Although I have to study HAM a few times more before I understand it  :-o

[GreatLor]

offtopic:

I see there are more nerdy ppl in here, guess what I did last night ?

*code*

start:
  move.l #cop,$dff080
  move.l #1,$dff088

eternal_loop:
  jmp eternal_loop

cop:
  dc.w ...
  [more..
   ..of..
   ..it]
  dc.w $ffff,$fffe

*/code*

WHat do you think, the worst ever intro or what ?  :-D  :lol:

[xeron]

GreatLor wrote:

WHat do you think, the worst ever intro or what ?  :-D  :lol:

Errm.. I think your startup code needs a little work Maybe this link will be of use to you? ;-)

[Thomas]

Startup code is ok, but I don't like the exit code. Usually you want to return to the assembler without reboot after the test.

Something like

mouseloop:
   btst #6,$bfe001
   beq.s mouseloop
;
;  restore system copper list here
   rts

is much more convenient.

Bye,
Thomas

[GreatLor]

Defender, whats this startup-code ?
oh, I DID some 2 one-screen demos back in 92-93, one of them used used huge fonts in a scroll, fonts that I drew myself in deluxe paint III I think it was, anyway I did both the graphic (phont) and the code pretty nice, that was fun, and also I drew a picture which I then coded a wave-effect to it (a pretty amateur one, nevertheless), but somehow I wasnt very fond of that OS stuff one had to code, so I just copied a routine to take care of things  :-P , thats pretty much what I did back then, oh I also tried horizontal starscrollers, but failed, cos I didnt know how to work with float-numbers in SEKA, well that was a little story from my amiga life, I hope you enjoyed me babbling nonsense stuff !  :-)

[Karlos]

*sniff*

Man, sometimes I actually regret getting a graphics card. Getting into harware banging was fun, but alas I sold my soul for RTG :-(

[GreatLor]

I know thomas, just didnt have time/energy to look in my VERY old mags hehe ! hey thomas, have you done any Intros or soomething ?