83 replies to this topic

[Synthpopalooza]

One more pic, again from Space Ace ...

The Atari ST original:



The PCIN pic:




This time I have managed to get the colors very close to the ST original. This required a slight adjustment of the color registers, as it seems G2F and AIS work off the PAL palette which is inaccurate. Also, the grey bit in the sky at the top, required adjustment of register 705 to a dark green, which when interfaced with the orange in reg. 711, makes a grey. To make greys, you blend colors from opposite sides of the color wheel.

Also, the blue part of the picture behind Ace flickers. This comes from blending white (710) with mid blue (register 712b, under graphics 10). It may require opening the fonts in ICE and trying a different color.

ATR is here:

 spsh.atr   90.02K   12 downloads

Edited by Synthpopalooza, Tue May 8, 2012 8:20 PM.

[Synthpopalooza]

Another PCIN pic, this time a digitised photo ...

Original:



PCIN pic:



I have improved the dithering algorithm, it will now dither inverse characters correctly using PF3.

ATR is here:

 clown.atr   90.02K   5 downloads

Run D:CLOWN.TUR

Next step: Try to render these in low-res PCIN using Antic 5 (96 scanlines). This will require a reorganzation of the Gr. 10 palette.

[Synthpopalooza]

I have successfully rendered the clown picture in low-resolution:



I call this display mode PCIN IRG. It is like PCIN except that this time the display uses ANTIC 5 (Graphics 13) mixed with Graphics 10, instead of Antic 4.

Differences in this display mode are, that since you can't use Antic 2, you have to use the graphics 10 palette under Antic 5. You still get all 9 Graphics 10 colors, but the paletting is different. Basically, we are only concerned with color combinations 5 through 11 in this mode, and they are laid out as follows:

Normal Characters: Inverse characters:

5 - COLP0 (704) COLP0 (704)
6 - COLP1 (705) COLP1 (705)
7 - COLP2 (706) COLP3 (707)
8 - COLBAK (712) COLBAK (712)
9 - COLPF0 (708) COLPF0 (708)
10 - COLPF1 (709) COLPF1 (709)
11 - COLPF2 (710) COLPF3 (711)

Notice that, in bold, color combinations 7 and 11 change when the character is in inverse ... specifically, COLP2 is replaced with COLP3 and COLPF2 is replaced with COLPF3. This is analogous to the Antic 4/5 color layout, where COLPF3 replaced PF2 when in inverse. This means of course that you cannot have P3 and PF3 in the same character cell with P2 or PF2.

With this limitation, your color resolution in PCIN IRG is slightly reduced from 34 colors to somewhere about 32.

The fonts in this picture were converted from normal Graphics 10 fonts, using an algorithm which converts the colors into their appropriate Antic 5 equivalents, and does substitutions with the next nearest color if there are any PF2/P2 and PF3/P3 conflicts. Where PF0-PF3 mix across modes, the pixels have also been dithered in a checkerboard pattern to reduce flicker.

So, basically, you now have a display mode which can show 32 colors at Graphics 7 resolution. You could theoretically use this as a bitmap mode, except that you would be POKEing into the character font memory instead of the screen memory to plot pixels, only using the screen memory to inverse a character anywhere you wanted to use COLP3 or COLPF3. The coordinate system would be different as well, but theoretically, softsprite routines could also be written for this display mode as well ... imagine using this mode for games like Space Harrier.

The ATR is attached. Run "D:CLOWNLO.TUR"...

Warning: This demo will only run accurately on a real Atari, or on Altirra versions 2.0 and up. There is an issue where color #8 (COLBAK) does not display correctly in this mode under most emulators (COLPF0 at 708 is shown instead). This bug was addressed and fixed with Altirra 2.0. In addition, earlier versions of Atari800Win will not display correctly the lowercase and control characters in this mode.

Next step: Doing CIN (Gr. 13+11) and MIN (Gr. 13+9) pictures in this resolution, followed by GTIA modes in this resolution (including HIP ... which should allow 35 shades monochrome in this resolution).

 clownlo.atr   90.02K   4 downloads

Edited by Synthpopalooza, Sun May 13, 2012 3:09 PM.

[Synthpopalooza]

A pic using MIN mode. Original:



MIN pic:



MIN is a combination of Antic 4 (Graphics 12) with Graphics 9. When used as a monochrome mode, you get somewhere about 25 usable shades of grey at 160 pixel resolution. While this is less than what you get in HIP mode (Gr.9 + Gr.10 and 31 shades), MIN has three advantages:

The image is sharper than in HIP modes, because the pixel layout is 2 Gr. 12 pixels blending with one Gr. 9 pixels, and no artifacts on either end.

You have the possibility of using PMG overlays with blending (which you cannot do in HIP mode), and thereby adding colors to your image (5 chroma x 25 luma, or 125 colors).

You can do a checkerboard dithering pattern (like in PCIN) in some areas of the picture. How this works in MIN is, the values stored in PF0-PF3 and the background color, are interleaved with the corresponding colors as they occur in the Graphics 9 picture. The result is a checkerboard pattern, which when blended makes a solid color, and less flicker.

Here is the .ATR. Run D:EYE.TUR ... next experiment will be to try to render this in lo-res ANTIC 5 (like the clown picture).

 eye.atr   90.02K   7 downloads

[Stephen]

That eye picture is awesome! It appears that the 25 shades of grey are freely usable?

[Stephen]

Looks great on the real machine. Bonus of my scan doubler, is no flicker on these 30Hz modes.

[Synthpopalooza]

Stephen, on Fri May 18, 2012 8:35 PM, said:

That eye picture is awesome! It appears that the 25 shades of grey are freely usable?

There is a limitation ... as the effect blends two Antic 4 pixels with one Graphics 9 pixel, 2 neighboring pixels cannot vary by more than about 2 steps. In addition, due to the limitations of PF3-PF2 in Antic 4, those two base shades cannot be in the same character cell. In this instance, shade values 4 and 8 under Antic 4 are used for PF2 and PF3.

The picture was generated by using G2F to make two sets of font files, one for Antic 4 and one for Graphics 9, and these are blended together, along with some dithering where common shades across both modes are evened out to reduce flicker. It is possible a better rendering algorithm could be made, that would smooth out the picture even more and reduce the flicker even further.

[Synthpopalooza]

The eye picture has now been rendered in MIN IRG. Three screenshots:



MIN IRG is a low-res version of the Super MIN mode shown in the previous post. The pixel resolution is the same as in Graphics 7, and has a slightly reduced shade usage, somewhere from 19-20 shades.

The main difference in this mode, from Super MIN, is the reduced number of shades. The reason for this is that it is required to use ANTIC 5 with the GTIA set to mode 9, as one of the base modes. Unlike setting the GTIA in Antic 2, using mode 9 under ANTIC 5 (a hardware mode I call Graphics 13.9) reduces the number of shades you can use. This is because ANTIC orders the colors differently. This color table shows how everything works:

Normal Inverse
0 - Color 0 Color 0
1 - Color 0 Color 0
2 - Color 1 Color 1
3 - Color 2 Color 3
4 - Color 0 Color 0
5 - Color 0 Color 0
6 - Color 1 Color 1
7 - Color 2 Color 3
8 - Color 4 Color 4
9 - Color 4 Color 4
10 - Color 5 Color 5
11 - Color 6 Color 7
12 - Color 8 Color 12
13 - Color 8 Color 12
14 - Color 9 Color 13
15 - Color 10 Color 15

You will notice that Graphics 9 colors 11 and 14 are unavailable here, which reduces your color resolution slightly. Each character cell is limited to 9-level shading, and the bit patterns shown in bold indicate where differing shades are available in inverse, Basically, the 4 brightest shades can only be used in inverse characters, along with shades 3 and 7, while the mid level greys 8 through 10 can only be used in normal (atascii<128) characters.

This requires a slightly different algorithm for converting greyscale pictures ... in the demos below, I simply converted the character to the nearest level grey based on the attributes (normal or inverse) of the corresponding Antic 4 character. It is possible that a better algorithm can be done, using screen flipping (i.e. mixing normal and inverse characters in the same character cell). It is also possible to rearrange the color paletting in ANTIC 5 so that PF3 is the brightest level shade, and PF2 the next shade down, so that the color palette better matches with Graphics 13.9.

The limitations therefore are: You cannot have mid level greys 8-10 in the same character cell as high level greys 12-15, and also, in Antic 5, the shade for PF3 cannot be in the same character cell as PF2.

It is possible also, that this mode could be used as a bitmap mode, with POKEs being made to the character font memory to plot pixels ... and perhaps a softsprite routine could be done as well. This is potentially a good mode to use for games similar to Zybex, R-Type, or Xenon, which require intricate color shading. Also, it is possible to use PM overlays in this mode as well to introduce other color shading as well.

An ATR is attached. Run D:EYEIRG1.TUR, D:EYEIRG2.TUR, and D:EYEIRG3.TUR

Warning: These demos will only run on a real Atari, or on Altirra version 2.0 or greater. Like the PCIN IRG modes, other emulators have difficulty handing the MIN IRG mode, the higher level ATASCII characters will not display correctly.

 eyeirg.atr   90.02K   3 downloads

Edited by Synthpopalooza, Mon May 21, 2012 5:32 PM.

[Synthpopalooza]

MIN can also be used to good effect for sepia tone pictures.

The original:



MIN pic:



It is not always necessary to use monochrome values for PF0-PF3 in this mode. With some variations in chroma, some very subtle and warm gradients can be had in this mode. In this case, the PF settings range from green-yellow to red-orange.

ATR below. Run D:ROSE.TUR

 rose.atr   90.02K   2 downloads

Edited by Synthpopalooza, Mon May 21, 2012 7:24 PM.