Synthpopalooza

I was experimenting with the ICE CIN editor on my Atari 1200XL and using Graphics 10 settings on modes 1 and 12, and I noticed some discrepancies in the display vs the way it looks on Altirra.

Specifically, Graphics 12.10 on the 1200XL is set up in the following manner, using bit quads:

0000 - 704 (background)
0001 - 704
0010 - 705 (p1)
0011 - 706 (p2) 707 (p3-inverse)
0100 - 704
0101 - 704
0110 - 705
0111 - 706 707 (inverse)
1000 - 712 (pf4 - graphics 10 color 8 )
1001 - 708 (pf0)
1010 - 709 (pf1)
1011 - 710 (pf2) 711 (pf3 inverse)
1100 - 712 708 (inverse)
1101 - 712 708 (inverse)
1110 - 712 709 (inverse)
1111 - 712 711 (inverse)

The problem is, Altirra shows 1000 to be 708, while it is 712 on the 1200XL. Do other Ataris show 712, or just the 1200XL

To test this, this program works:

10 GRAPHICS 15:POKE 623,128:POKE 712,14
20 COLOR 8
30 POSITION 0,0:XIO 18,#6,0,0,"S:"

On Altirra this will show orange (708) but on the 1200 XL it shows white (712).

I've noticed Graphics 1.10 (1 with GTIA set to 10) also has differing colors from Altirra and other emulators.

Could someone test this on other real Ataris (130XE and 800XL specifically) to see if they get the same results?

Apologies in advance if I am treading old ground ...

I was doing some experiments in my ICE CIN editor, on my Atari 1200XL, and came up with something strange.

Firstly, I was doing a character dithering experiment in the Super PCIN mode (this is Graphics 10 mixed with Graphics 12). When mixing these modes, the playfield registers 708-711 are used in both 10 and 12, So, I tried plotting a checkerboard pattern using the same two pairs of colors. The pictures below in Altirra illustrate this:

 super pcin dithering frame 1 (gr.12).png   8.72K   36 downloads  super pcin dithering frame 2 (gr.10).png   10.47K   40 downloads  super pcin dithering frame result.png   9.69K   44 downloads

In this example I blended PF1 and PF2 on alternate VBI frames. In the altirra screenshot I got a solid color field, however when I did this on my Atari 1200XL, I noticed the pixels had a slight variation in brightness. Further experimentation showed that Pf0-PF3 in Graphics 10 is 1/2 step brighter than the PF0-PF3 in Graphics 12.

I also did the same thing in Super MIN (Graphics 9 + Graphics 12) mode:

 super min dithering pair frame 1 (gr.12).png   7.68K   38 downloads  super min dithering pair frame 2 (gr.9).png   8.25K   34 downloads  super min dithering pair result.png   7.42K   29 downloads

In this case I blended PF0 in Graphics 12 with the accompanying shade in Graphics 9. Again in Altirra this created a solid color field, but on the 1200XL I noticed that the Gr. 9 pixel was brighter. Further experimentation showed that this pixel was 1/4 step brighter than the Graphics 12 pixel (1/2 of a Graphics 9 luminance step!)

Questions: Can anyone with a real Atari verify this? And would the results be the same if we did this in bitmap mode (Graphics 15+10 or Graphics 15+9) by alternating modes each scanline? Or is this unique to the 1200XL?

One caveat: if you blend 15 with 10, you will also need to adjust HSCROL by one color clock on the GR. 15 lines so that the pixels will line up with the Gr. 10 pixels (the HIP bug).

Well, looks like my font editors won 4th place in ABBUC.

ICE is a series of font editors that work with special character-flip text modes that enable the display of extra colors onscreen through VBI swapping. There are 20 different graphics modes supported, which can display anywhere up to 256 colors onscreen at once.

Attached are three ATR's, plus the insctuction manual as a .PDF, and also some articles I wrote for AtariUser documenting most of these new Graphics modes.

To use ICE, I recommend any Atari with 64K RAM. You can run this on a PAL machine, but NTSC gets better results because of the faster refresh rate. For Emulation, Altirra is recommended. Atari800Win is not recommended because there are issues with displaying some of the CIN modes, and the screen flicker refresh rate is horrible on it.

The ATR's are:

iceirg.atr - Edits in Super 0, Super IRG, Super IRG 2, and DIN
icegtia.atr - Edits in the GTIA modes (including Super 9, Super 10/10+, APAC, and HIP)
icecin.atr - Edits in the CIN modes (3 variations each of CIN, MIN, and PCIN)

I will be working on updates to these programs as I get time, and also I am working on new ICE editors for the Super IRG modes based out of Graphics 1. Examples of these modes can be seen in this thread.

Some screenshots:

 ice irg title.png   6.43K   68 downloads
 ice cin title.png   6.52K   72 downloads
 cin 12 character edit.png   8.67K   60 downloads
 din color tuner.png   8.06K   50 downloads
 din-mario.png   9.11K   42 downloads
 apac.png   8.09K   42 downloads
 super irg 2.png   8.25K   45 downloads
 super 10 color tuner.png   7.03K   36 downloads

I feel the urge to experiment with the new ICE modes used in my editor ... specifically, I want to work out a way of converting GIF/JPG into Super IRG 2 ... that is, 160x192 pixels (128 across in narrow mode) with 16 colors per char and 23 colors onscreen at once.

I have no idea how to even begin to program an algorithm that can reduce a GIF/JPG to 23 colors that will work in Super IRG 2, there are a lot of variables ... firstly, how to select 8 component colors (plus the background) which will blend to make the 23, and also allowing that 7 of these 23 colors will only be usable in inverse (ATASCII>128). The idea is that PF0-PF3 get flipped every vblank to make the 23 colors, with the 7 component colors made off of PF3 usable only in inverse.

My best bet, until someone can write such an algorithm, is to find a PC program which can reduce any image to 23 colors, and try to transcribe the image by hand into my font editor, and also try to calculate by hand the best colors to use in ICE based on the colors in the original image. Gonna be a pain in the arse, but I want to try.

So, suggestions on which PC paint/image program to use would be appreciated.

If I get good results from this, I may also try other modes like the PCIN ones (Graphics 12+Graphics 10) and Super 10/10+ (45 to 80 colors at GTIA resolution), which rely very heavily on color indirection (i.e. setting color registers) and less on monochrome/chroma settings like in APAC, HIP, or CIN.

I have been brainstorming, and something occured to me, after looking at the APAC article from the 1989 Analog issue ...

Is it possible to switch between 2 APAC mode screens every VBLANK? I think this could be achieved by reserving memory for 2 graphics 8 screens, setting up 2 display lists in memory which point to these 2 screens and have them call each other, then activating APAC mode.

Because the Gr. 11 and Gr. 9 lines overlap each other, you get 256 colors without flicker ... then by flipping the screens 60 times a second, the color resolution increases to about 32,767 colors or thereabouts, in theory. You'd still get the blank scan lines in the picture and the resolution would be 80x96. Of course this could also be done with Graphics 15 to increase resolution, with the color resolution decreased to something like 4.096 , with 4-level shading. You could have nice photo quality color resolution with this, almost into Amiga territory when it comes to color palette resolution.

I am going to attempt a test to see if this can be done, but I am wondering: What is the best way to set up screen flipping in Gr. 8? Reserve memory below ramtop for 2 Gr. 8 screens, and then 2 display lists which call each other?