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Rendering APAC in Altirra

altirra Atari800MacX

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#1 Spaced Cowboy OFFLINE  

Spaced Cowboy

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Posted Sun Apr 22, 2018 4:30 PM

So I'm playing around with some APAC conversion, and I'm having some issue with getting the correct colours when running on Altirra. I know the precise colouration of the emulator isn't a goal, but my results are wildly different from what I expected...

 

Here's an image showing what I mean. The left image is the input PPM (portable pixmap) file as mapped to the Atari's NTSC colour table, the middle image is the resulting APAC BGP file, as rendered by Atari800MacX and the BugBiter240i Pic viewer v3.0. The third image is the same image, run within the same pic viewer, as viewed in Altirra 2.9. PS: click on the thumbnail to see the image, there's no banding in the real middle image.

 

emulator-apac-renders.png

 

 

Now both of these are set to NTSC with XL/XE artifacting. Atari800MacX is set to 'smooth' scale mode and Altirra has 'Frame Blending' set on. I know Phaeron has said that you have to tune the colours for your own monitor, but do they really start this much off ? Or is something else going on here ?

 

I know there's a version-3 of Altirra out, but 2.9 is the latest one I know of that's been configured to "just work" out of the box on a Mac. I know nothing about windows machines (I can count the number of times I've used one on one hand) or configuring Wine, so I'm using what someone else has made available.

 

The code to do the convert is available at my GitHub account - if you have a Mac with Xcode, it ought to compile straight off.

 

Any ideas ?

 

Cheers

   Simon



#2 Stephen ONLINE  

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Posted Sun Apr 22, 2018 4:57 PM

I believe for the BugBiter image viewer to work correctly, you need a PAL setup?  I would try that first.  That being said, there have been numerous updates to the emulator, I would highly recommend running the latest version, even if not for this specific issue.



#3 Spaced Cowboy OFFLINE  

Spaced Cowboy

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Posted Sun Apr 22, 2018 5:32 PM

Ah, so maybe Altirra is doing a *really good* job of emulating the real hardware then :)

#4 Rybags OFFLINE  

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Posted Sun Apr 22, 2018 5:51 PM

You might need to play with the video options.

 

System->Video:

Pal, NTSC shouldn't matter though real NTSC TVs won't do colour blending.

Artifacting should be set to PAL.

Frame blending shouldn't matter though can help to reduce flicker in modes like TIP and ones that change colours or graphics at a given location to give the impression of more colour or better resolution.



#5 Spaced Cowboy OFFLINE  

Spaced Cowboy

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Posted Sun Apr 22, 2018 6:12 PM

Yeah, switching to PAL really makes a difference in Altirra... This time with original on the left, and Altirra (PAL mode) on the right

 

emulator-apac-pal-render.png

 

 

I may have an off-by-one in my code, because it looks as thought the reds are being chosen over the (correct) browns. Strange that the grays are correct then, though.



#6 Stephen ONLINE  

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Posted Sun Apr 22, 2018 7:17 PM

So I'm playing around with some APAC conversion, and I'm having some issue with getting the correct colours when running on Altirra. I know the precise colouration of the emulator isn't a goal, but my results are wildly different from what I expected...

 

Here's an image showing what I mean. The left image is the input PPM (portable pixmap) file as mapped to the Atari's NTSC colour table, the middle image is the resulting APAC BGP file, as rendered by Atari800MacX and the BugBiter240i Pic viewer v3.0. The third image is the same image, run within the same pic viewer, as viewed in Altirra 2.9. PS: click on the thumbnail to see the image, there's no banding in the real middle image.

 

emulator-apac-renders.png

 

 

Now both of these are set to NTSC with XL/XE artifacting. Atari800MacX is set to 'smooth' scale mode and Altirra has 'Frame Blending' set on. I know Phaeron has said that you have to tune the colours for your own monitor, but do they really start this much off ? Or is something else going on here ?

 

I know there's a version-3 of Altirra out, but 2.9 is the latest one I know of that's been configured to "just work" out of the box on a Mac. I know nothing about windows machines (I can count the number of times I've used one on one hand) or configuring Wine, so I'm using what someone else has made available.

 

The code to do the convert is available at my GitHub account - if you have a Mac with Xcode, it ought to compile straight off.

 

Any ideas ?

 

Cheers

   Simon

Cool - I did a PC based image to BGP convertor some years back.  I never finished it.  If you want my source code (C#.Net) you're welcome to it, just PM me.  It can do bulk processing, image re-sizing, several dithering methods.  It can also populate the meta-data in the BGP files (image description, long filename, etc.)  I did not yet get around to supporting the higher res CIN files.



#7 Spaced Cowboy OFFLINE  

Spaced Cowboy

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Posted Sun Apr 22, 2018 7:30 PM

So after playing with the *real* Altirra palette, rather than the NTSC standard palette, I get the below...
 

altirra-palette-rendering-apac.png


Respectively, the original data, the palletized ready-to-convert-to-BGP image, and the result. I think that's pretty good. I also found a bug in the code when using palettes of 256 colours rather than the 128 colour palette I was using...

#8 Rybags OFFLINE  

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Posted Mon Apr 23, 2018 5:24 AM

When converting pics you can help out by doing some pre-processing externally at times.

 

I've found that in general pics will convert better if the colour saturation is increased before processing.

Also you'll get colour assignment errors, often in the region of red becoming purple, brown becoming red, blue going greenish or any colour becoming greyscale (ref sat-boost to help).

Misasignments can come down to which palette is being used to assign to the Atari.  Also remember that PAL/NTSC colours are slightly different.







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