Using Atkinson Dithering
For every input file, tohgr will produce two output files: One is another file that approximates the appearance of the original image in Apple II hires or double hires graphics. The other output file is an Apple II file, which can be viewed on an Apple II computer. Hires and Double Hires files can be either raw memory images, which you can BLOAD into memory to view, or filetype $08 packed graphics images. Double hires memory images are stored as an 8192 byte auxiliary memory image followed by the 8192 main memory image. Super Hires images are stored as Apple Preferred Images (filetype $C0/$0002).
A Note About Super Hires Conversion: I am not currently really satisfied with the conversion to Super Hires. The results are decent but it takes too long. The conversion works by attempting to find a good palette for dithering each line by repeatedly dithering the line and improving the palette. The improvement step I use is not very great and acts to equalize the error between a palette entry and the each of pixels it replaces instead of finding a palette entry with minimum total error. This process tends to find local optima and so after each local optimum is found I randomly perturb the palette and repeat the iteration. The quality parameter "-q" listed above specifies how many times this will be attempted before giving up and using the best palette found so far.
| Original Image | Approximate Hires Appearance |
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Using Atkinson Dithering |
| Original Image | Approximate Double Hires Appearance |
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| Original Image | Approximate Super Hires 3200 Color Appearance |
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