Colors on the Amiga

[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 :-(

[Karlos]

LocalH wrote:
...but with 16 independent colors per scanline (IIRC)? What was the name of that mode?

That was SHAM (sliced HAM) or something wasn't it? I remember there was a HAM8 derived version that could get so close to 24-bit you'd struggle to tell the difference.

There was also a strange 15-bit emulation that used the old HAM6 laced mode. Each pixel was split into two (vertically) where the least significant bits of the 15-bit data were split between the upper and lower pixels.

So, suppose you wanted to show the lowest level of grey possible in 15-bits, the upper pixel would have 12-bit RGB values of 1 1 1 and the lower pixel would have 12-bit RGB balues of 0 0 0. This pattern of upper/lower was inverted every pixel to produce a regular dither pattern to improve the effect.

The eye thus saw one larger pixel as an average of the two colours and you got the effect of an extra bit of precision for each channel.

It was pretty simple, but effective :-)

The downside was you couldn't show images that were taller than the lowres mode because effectively the onscreen image was doubled.

[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.

[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.