How do you choose the major options for your destination image?
The destination image is what RastaConverter will use to evaluate all of its attempts to see how close it has reached the "ideal" 8-bit image. (It the window with three images, it is the image on the right.) Getting the right destination image is super-important, because you might burn through hours of CPU time in trying to reach it. You need to optimize your destination image before you spend so much time trying to find the closest match.
I generated the following 216 combinations:
6 FILTER options (used to scale the image): lanczos, box, bicubic, bilinear, bspline, catmullrom
4 PREDISTANCE options (used to set colors): ciede, euclid, yuv, cie94
9 DITHER options (used to mix colors): chess, floyd, 2d, jarvis, simple, knoll, line, line2, none
There are other choices which affect the destination image, such as DITHER_VAL, DITHER_RAND, BRIGHTNESS, CONTRAST, GAMMA, and PAL (color palette). For the purpose of the comparison, these values were kept the same.
I've attached the results (along with the larger source picture) as a zip so that you can closely examine the possible effects of each option. Knowing what I know now, I would select totally different options when trying to build my destination image.
In general, the PREDISTANCE option will affect overall color selection and placement, and DITHER will affect the way it tries to mix the limited set of colors to best match the original picture. In this example, FILTER had little impact, but in other experiments, I've seen fine details preserved or hidden based on the choices.
ANIMATED GIF (the original image will be held for 10 seconds):
This animated GIF should give you a quick preview of the difference that these selections will make, and really, I think it doesn't show the differences very well. You can inspect the individual files in detail from the attached ZIP, and come to your own conclusions.
ZIP FILE (all 216 combinations, animated gif, full-sized original):
creative.zip 39.66MB 10 downloads
The major observations that I made were that the 2d, chess, and floyd DITHER options can mix totally unwanted colors into an area. The line, line2, and none DITHER options create nice horizontal lines which, if you like the overall picture, should convert into a picture which is very close to your destination image. The PREDISTANCE options, as mentioned, change what overall colors are selected and in what areas. (The top of the large moon in the center and the giant robot's body are two main places to see the effects.) Overall, the output of the ciede option is the most unique of the four.
Finally, I wanted to acknowledge the artist, Paul Stinson. I believe he created this image in 1978? It was used for the April 1982 cover of Creative Computing, and it was also the front cover of the book The Road to Science Fiction #2 From Wells to Heinlein. He has created other works, such as the repackaged box art for Sierra On-Line's The Wizard and the Princess adventure, also in 1982.
Paul was kind enough to send me a higher resolution copy than what I could find online. He also seemed pleased that people were still interested in his work from so many years ago. It seems appropriate that we're converting and displaying this vintage sci-fi artwork on a vintage piece of hardware from 1979.
EDIT: Here is the Windows batch file that I used to create the full set of images. The directory paths are hard-coded, but if you can do some simple editing (and/or create the same directories), you can produce a wide set of destination images to select from before you decide on a fine one.
WINDOWS BATCH FILE (two lines, and the second command is all on one single line):
for %%f in (lanczos, box,bicubic,bilinear,bspline,catmullrom) do for %%d in (ciede,euclid,yuv,cie94) do for %%g in (chess, floyd, 2d, jarvis, simple, knoll, line, line2,none) do start /low /wait d:\atari\rasta\rastaconverter.exe d:\atari\rasta\IMAGES\%1 /pal=ntsc /threads=2 /predistance=%%d /dither=%%g /dither-val=1 /dither_rand=1 /filter=%%f /s=1 /h=240 /init=smart /o=d:\atari\rasta\OUTPUT\%1-%%f-%%d-%%g /preprocess
Someone could probably make this a lot friendlier.
This assumes that the RastaConverter software is in the D:\atari\rasta directory, the source images are in D:\atari\rasta\images and the output is placed into the D:\atari\rasta\output directory. Put this into a batch file like "prepoc.bat" and then supply the filename from the images directory to convert, such as:
D:\Atari\RASTA> preproc.bat creative.png
Happily, it launches the conversion with a low priority so it (generally) won't interfere with everything else running on your box. Be sure to increase "/threads=2" if you have a machine with lots of horsepower. Change "/pal=ntsc" if necessary outside of the US and Canada.
Edited by jmccorm, Mon Jan 1, 2018 2:28 AM.