Posted By
IstvanV
on 2008-02-11
14:22:52
|  Re: plus4emu 1.2.5.1
Gaia: it is of course impossible to guarantee a lossless conversion of C64 multicolor graphics with any (even FLI) video mode on the Plus/4, but if the image is not too complex, it is possible to get acceptable results even with the current version of the converter. One major limitation is that there are not too many video modes that are currently supported, basically the choices are either 304x200 interlaced multicolor FLI (this can also be increased to up to 248 lines), or simple 160x200 multicolor graphics without FLI. The high resolution interlaced FLI converter, while great for many photo-realistic images, probably does not work very well for this purpose.
For good results, the input image should be resized to 608x400 when using the multicolor FLI mode, or 640x400 for the simple non-FLI mode, with no interpolation. This is because the converter first resizes the image to the above mentioned resolutions with sinc interpolation, and then to the actual output resolution with simple pixel averaging. Also, in the conversion parameters dialog, all scaling, color correction, dithering, etc. should be disabled, as shown on this screenshot: http://www.sharemation.com/IstvanV/flitest/fliconfig1.png
To see how well this works in practice, I have converted this random screenshot from a C64 multicolor image:
http://www.gfxzone.org/personal/mermaid/02/mermaid-jungle.html
The resulting PRG files are:
http://www.sharemation.com/IstvanV/flitest/mermaid-jungle.prg
http://www.sharemation.com/IstvanV/flitest/mermaid-jungle_fli.prg
Of course, the palette is different, so that is probably the difference that is easiest to notice.
Note that I manually modified the X shift table in the second program (using the 'sr' command of the plus4emu debugger) to remove the horizontal interlace effect, and it does still store the whole image twice. Obviously, a non-interlaced multicolor mode would be useful here. It also does not use the improved FLI code discusses with Dr. Death that is still to be implemented, so it would be possible to get better quality.
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