Another (enhanced) Spectrum 512 slideshow for the Atari STE

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Anima
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Another (enhanced) Spectrum 512 slideshow for the Atari STE

Postby Anima » Tue Sep 20, 2016 10:28 am

Here's another (enhanced) Spectrum 512 slideshow for the Atari STE but this time the maximum number of colours has been raised to 32768 (of which the Atari STE is only able to display up to 29791). The Archive includes one folder of the slideshow to copy the files directly to your Atari HD and an .ST floppy image with the same content from which you can boot.

The method of switching two images and/or palettes is not really new since other graphic converter tools like Doug's Photochrome offer such a feature in a more advanced way. Also the Spectrum 512 format does not support overscan resolutions and can be considered being a rather outdated format. OTOH it's quite a well known format and supported by STOS and other programs.

So what's the real reason to make another Spectrum slideshow?

Well I noticed that the colours stored within the Spectrum 512 image didn't use the whole 16 bit colour word. In fact, it uses only 4 + 4 + 4 = 12 bits for the Atari STE. So I thought it could be cool to add another bit to increase the colour channels to 5 bits each. The new least significant bit for each channel are now stored in the upper nibble of the colour word and so the image .SPU format itself is kept completely "backwards" compatible. Fortunately, since the added bits are being stored in an unused space the (uncompressed) .SPU image size doesn't even change.

With this new additional colour bit information the display program generates two palettes but not two images(!) to switch alternatively between them in the VBL routine.

Here are some of the slideshow pictures and how they look on the Atari STE:
Image Image
Image Image

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Re: Another (enhanced) Spectrum 512 slideshow for the Atari STE

Postby marss » Tue Sep 20, 2016 12:08 pm

superb

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Eero Tamminen
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Re: Another (enhanced) Spectrum 512 slideshow for the Atari STE

Postby Eero Tamminen » Tue Sep 20, 2016 6:39 pm

Looks great on Hatari too!

(Quality difference between ST & STE is especially visible in the first pic, on ST there's very visible banding in the blue sky.)

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Re: Another (enhanced) Spectrum 512 slideshow for the Atari STE

Postby metalages » Tue Sep 20, 2016 9:29 pm

I have used this trick to put LSB for color flipping into bits 12,13,14 of palette words in Synthetic Arts 3 (extended palette) :)
In my case it was just for enhanced palette (but only 16 colors at the same time).
Anyway it was a good way to store enhanced palettes into usual formats (neo, pi1...)
http://cyber.savina.net/synthy/synthy.htm

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Re: Another (enhanced) Spectrum 512 slideshow for the Atari STE

Postby lp » Tue Sep 20, 2016 9:30 pm

Very cool. I tweaked my Spectrum codec for zview to load these. Below is a snapshot of Falcon high-color test.

spec512-5bit-test.png
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Re: Another (enhanced) Spectrum 512 slideshow for the Atari STE

Postby metalages » Tue Sep 20, 2016 9:34 pm

Also used this for high colors images here :
https://github.com/gibs75/demOS/blob/ma ... C/SLIDES.C
(SlideDeployPaletteFlipAndMask and SLIinitDeployer)

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Re: Another (enhanced) Spectrum 512 slideshow for the Atari STE

Postby Anima » Wed Sep 21, 2016 6:37 am

metalages wrote:I have used this trick to put LSB for color flipping into bits 12,13,14 of palette words in Synthetic Arts 3 (extended palette) :)
In my case it was just for enhanced palette (but only 16 colors at the same time).
Anyway it was a good way to store enhanced palettes into usual formats (neo, pi1...)
http://cyber.savina.net/synthy/synthy.htm

Shame on me I didn't even know that program. That looks really cool. I already wondered if someone else has done it before because it is quite obvious to put more colour data into it (like Atari did with extending the hardware colour registers). Thanks for pointing that out.

lp wrote:Very cool. I tweaked my Spectrum codec for zview to load these. Below is a snapshot of Falcon high-color test.

Great! Thanks mate.

A short note how to generate these images. Please visit the Retro Image Tool website and choose "32768 (?)" for the colour palette shown like in the following screenshot (marked red) and save it.

Image

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Re: Another (enhanced) Spectrum 512 slideshow for the Atari STE

Postby metalages » Wed Sep 21, 2016 2:30 pm

Synthetic Arts was quite well spread in France as it has been provided on both ST magazine and Atari magazine cover disks, but seems it was not really the case elsewhere in Europe ;)


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