Colors on the Amiga

[pwest]

Interesting stuff about the SHAM and the vertically split ... ie two vertical pixels representing a color, thing... although obviously that would suffer a resolution penalty.

Another technique for a slightly flickery display just came to mind ... I don't know if anyone ever tried this but it would give the illusion of billions of colours....

I don't know exactly how fast screen/palette switching is on graphics cards these days .. I seem to remembering it was more difficult to synchronize such things with the vertical blanking cycle on gfx cards than it was on the old OCS/ECS/AGA chipsets. .. but anyway...

What if you had two versions of an image. One image has color precision rounded down to the nearest available colors, and the other has the color precision rounded up. Then you flip between the two images at 50/60fps so that each image is displayed for 1 frame.

The colors in the one image would seem to combine with the colors in the other image to produce a hybrid color?

For example, taking it to an extreme, black pixels in one image would combine with white pixels in the other to produce a grey?

Of course you wouldn't have to use only black and white. You'd use as many colors in each image as possible. If there was scrolling, both frames would scroll together... even if there is a 50fps refresh this produces the effect of it being a 25fps refresh.

It halves the refresh rate, but the illusion of a third color is produced for every pixel based on the combination of the two colors to the eye. Even if you only had 12-bit color in each image, surely this would give you an illusion of 24-bit color.. if not a lot more? I don't know what the exact formula would be.

I don't even know if the illusion would work but it would sure work BETTER if the refresh rate was high enough ... eg a 100hz refresh would produce a screen at 50hz with flips between screens being one flip per cycle. It would give you a 50hz screen with a whole lotta colors?

I haven't tried it, like I said, to see if the illusion actually holds up and if the flip is fast enough to make the effect, but hey... this just came to me and I don't have an Amiga. Maybe someone can try it and let us know if it works.

Imagine how many colours you could potentially have if you used the 18-bit color palette of AGA and flipped between two slightly differently colored versions of the same image? .... all those hybrid colors.. .36bit color?

[pwest]

Also the colors in each image would only be SLIGHTLY different from each other probably, greatly reducing a flicker effect, since flicker is caused by contrast?

[pwest]

Somebody could test using two 12-bit images whose `combined color` produces the correct 24-bit color. .. and compare it alongside the original 24-bit image, see if the colors look the same?

[Karlos]

@pwest

Sorry dude, it doesn't quite work that way. If you add 2 x-bit numbers, the maximum result is an x+1 bit number. You get a 2*x bit number when multiplying, not adding.

So, if you think of your RGB 444 values, adding two together (like the vertical split system) gives you 555, since you are adding each 4-bit channel.

This is exactly what the fake 15-bit mode depended on, it did the rounding up and down for each laced pixel comprising one "normal" pixel.

[aardvark]

All A500 models had EHB.

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

 :smack:
I don't think so.  My A2000 originally did not have the Denise chip that enabled half-bright mode.  I purchased it and added it in later.  So I surmise that A1000s did not have them originally either, nor A500s produced about the same time as my A2000.  (Were A1000s still produced after The A500 and A2000 came out?)

[Piru]

@aardvark

That's quite interesting, considering OCS Denise does EHB.

Perhaps some old stock of pre-OCS chips were used on some machines?

[leirbag28]

@ LocalH


 You are probably talking about a program such as BROADCAST TITLER 2.0........................it allowed 320 colors on screen at once................16 per line?
it also had the SupeHiresMode (1440x480) or something like that. And on ECS  4 colors per line on the SuperHiresMode..............now when I say per line........I mean for each line of text you wrote....and it could smoothly change colors.

I still cant believe it every time I run it on my A600.it looks quite nice.

this program is still awesome today...........I love it..........its probably the best Character Generator on the Amiga (Besides the ToasterCG or Montage)............not even SCALA can match it in terms of the quality of the characters.

Also wanted to add that Brilliance 2.0 had the ability to paint on HAM without showing fringing like most other paint packages.

Also have a game called OverLander(Trainer).its a car game kinda like RoadBlaster or MadMax.........where when the game starts to load.it display an apparently more colors than HAM image with no fringing of a the Overlander Logo with a red car at the bottom............this is the highest quality HAM image I have ever seen on any OCS/ECS Amiga
I still cant figure how they did it and why no one else used this technique

 Oh, and as far as I know........WinUAE cant run Broadcast Titler 2.0

[Hattig]

Whoa, lots of dots there … use … … an ellipsis!

…

nice, eh?

Yeah, it was possible to achieve a lot of nice effects by programming the graphics chip in the Amiga, a lot of people never bothered to learn it that well though because the default stuff was so good.

Btw, I never thought much of EHB mode on the Amiga. I think that it would have been much better to use the 6th plane as an inverse plane. I.e., black → white, red → cyan. Would have allowed for a lot of extra colours in games instead of just darkening games (although useful for shadows, e.g., in Settlers).

[pwest]

@Karlos

Well excuuuuuuuuuuuuuwze me!

Well then it *at least* doubles the number of colors.

If I have a 16 color palette on one screen and a 16 color palette on the other, and I flip the two images quickly, I'm not just going to see 16 extra colors.

Each individual color in one screen is going to combine with each individual color on the other screen. Surely it's more something like the number of colors are squared. We're talking about how many unique combinations. I know there is some formula for that like something to do with N^2 or something cosmic.

Anyway, numbers aside, I still think it would produce more colors than normal and not require chunkier pixels or extra rows being wasted. It can be full resolution.

Somebody try it?

[pwest]

I thought EHB was standard on the A500, at least on my revision.

[Hattig]

@pwest:

Many C64 graphic "modes" use this method to ge decent looking images.

If you kept the palette constant, and switched between two screens you'd get a possible 136 'colours' on screen (I worked this out previously on an Amstrad CPC forum, heh). A lot of these would be too flickery to use though, so you'd get more like 60 usable colours. As a picture also has colour gradients in the palette already the options reduce even further.

Changing palettes between screens wouldn't work either. If you want white in a picture, you've got to have white in both palettes. Same with black, and any other colour!

[Hattig]

@Kephren:

Lionheart was one hell of a game graphically.

Considering that it was OCS and ran great on an A500 ... and from what I could see ran in two playfields, both 8 colours, the fact that there must have been hundreds of colours on screen at the same time due to clever copper manipulation ... whoa. And then it had that 3D backdrop (like the floor in SNES Streetfighter 2) of marshes on the first level.

Dammit, I must play that game again. Pretty damned difficult though.

[Karlos]

pwest wrote:
@Karlos

Well excuuuuuuuuuuuuuwze me!

Easy matey - I wasn't flaming you or anything :-D Blimey!

I actually see what you're driving at with the idea but see the other posts before this one to see what would possibly happen.

I think the actual number of colours would be some permutation rather than a simple double or the square. I mean if you think about it, some combinations will be equivalent - eg if screen 1 had solid blue and screen 2 solid red, you'd get the same magenta as you would if screen 1 was red and screen 2 blue.

[Jose]

Shouldn't be to hard to try. Just use the copper to alternate between two screens. Or even use different images for an interlaced screen.

[Georg]

Lionheart was one hell of a game graphically.

Considering that it was OCS and ran great on an A500 ... and from what I could see ran in two playfields, both 8 colours,

In two-playfield mode the one in the front only shows 7 colors, because one is transparent and makes the back-playfield show through.