Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!lll-winken!uunet!mcsun!unido!ira.uka.de!fauern!faui43.informatik.uni-erlangen.de!lsmichae
From: lsmichae@informatik.uni-erlangen.de (Lars Michael (AKBP WS 1990))
Newsgroups: comp.sys.atari.st
Subject: Re: Spectrum 512
Keywords: spectrum, picture format
Message-ID: <1991Jan29.113557.14106@informatik.uni-erlangen.de>
Date: 29 Jan 91 11:35:57 GMT
References: <4722@ruuinf.cs.ruu.nl>
Organization: University of Erlangen, Germany
Lines: 63

avgroeni@cs.ruu.nl (Annius Groenink) writes:


> Is there someone who can give me some information about
>the way Spectrum pictures are showed? I know the file format,
>but that's not enough to write my GIF-Spectrum 4096 converter.
>I'd like to know what exactly is done with the 3 palettes
>that go with each line.
> 
> Annius Groenink

Let`s have a lot a the umcompressed format:

<Spectrum umcompessed>		.SPU

	   80	Words	Scan line 0 is unused (color set to black)
	15920	Words	199 Scanlines
	 9552	Words	199 * 3 * 16 Colors
-------------------------
	25552   Words	=	51104 Bytes


Now we one scanline and the according 3 Palettes (16 Colors each):

Color  0 of Palette 0 is the border color and set to black.
Color  0 of Palette 1 is set to black.
Color  0 of Palette 2 is set to black.

Color 15 of Palette 0 is set to black.
Color 15 of Palette 1 is set to black.
Color 15 of Palette 2 is set to black.

The other colors (0 < c < 15) are useable from left_border to right_border
(inclusive):
(All values are x-koordinates of the lowrez screen.)


				left_border		right_border
Palette 0:
Color c = 2*n+1 (odd):		0			10*c - 6
Color c = 2*n (even):		0			10*c - 1

Palette 1:
Color c = 2*n+1 (odd):		10*c - 5		10*c + 160 - 6
Color c = 2*n (even):		10*c			10*c + 160 - 1

Palette 2:
Color c = 2*n+1 (odd):		10*c + 160 - 6		319
Color c = 2*n (even):		10*c + 160		319

E.g. Point number 147 in the scan line has color 5. From which palette does it
come from?
		c = 5 (odd)

Palette 0		Palette 1		Palette 2
0 .. 10*5-6 = 44	45 .. 204		205 .. 319

=> This is a color from palette 1.

BTW I would be interested in your gif shower. Please post it when ready.

"May the Schwartz be with you!"
									Lars