How many colours on a Genesis bitmap?

[maiki]

I was just thinking about this playing Lethal Enforcers yesterday. I think the digitized bitmaps in the game are something like 16-coloures like.

Isn't it a bit low considering the Genesis should be able to display 64 colours at once?

I think it is perhaps not 64 colours per layer, but each layer is perheps limited even more???

Who know the true?

What is the maximum color depth you could digitize a bitmap into on a Genesis?

 

[antime]

Each 8*8 tile can choose colors from a 15-color palette. There are four palettes total, and each palette entry has three bits per component.

That's the basic spec. In addition, there's shadow/highlight mode and tricks like rewriting the palette entries while the image is being generated.

 

[LocalH]

Technically, without using techniques such as interlacing (C64-style interlacing where you alternate between two images each frame, not VDP hardware interlacing), the Genesis can pull from a total pallet of 1536 colors. This comes from the 512 colors that can be generated directly (3 bits per component, 8*8*8=512), plus the same for both shadow and highlight mode.

Now, in a practical sense, you'll only get 1536 colors on screen simultaneously with raster tricks. Charles MacDonald made such a demo, IIRC. Without special tricks, you're limited to four 16 color pallets, with color $0 of each pallet only usable as a backdrop color. Each layer can use any of the four pallets, as can sprites. This means that there is somewhat wide flexibility in how the programmer utilizes the various VDP facilities (for example, you can have parallax scrolling by using each layer separately, with 15 colors per layer, or you can combine layer A, B, and sprites to get 60 colors, and if you tweak the backdrop you can eke out a tiny bit more color in some instances). As antime mentioned, you can also change pallet entries mid-frame, to gain even more colors (this is how the Sonic games implement water). I haven't played around with this much, but while you can't update all the pallet entries every line due to lack of Hblank time, I would surmise that it should at least be possible to tweak the backdrop register on every line, and possibly mid-line.

 

[maiki]

So, in practical point of view, The Lethal Enforcers are using the maximum available. (?) Because I can see both layers and sprites being displayed at once.

Konami Genesis team rules, anyway.