A loose collection of image related PHP scripts for C64
I find myself with various image files that I need to convert to or from C64. It is easy enough to write a short PHP script to process the bits. They're so useful for me that I thought I'd share them on GitHub so other people wouldn't have to write them themselves.
They use the MIT license. Only because, I couldn't find the "Do whatever you like" license. But really, do whatever you want with these.
I found a great little tool called HiRes:
Use it at https://dschwen.github.io/hires/
This was apparently developed for a pixel art contest for Stirring Dragon Games' Unknown Realm.
It's really great, very simple. Imports from an upload, saves your current work to some sort of browser local storage. And you can download at any time, as PNG. The problem is that you then have the image file as a PNG. What I really want is to take that PNG and convert it to a true hires image file format, for use in a C64 program.
The conversion is quite simple. It's more or less the inverse of what "renderer.php" does. The tricky bit is mapping the colors back to the C64 color data. This is what color-palette.php is for. I used HiRes to create an image that just has the 16 colors up in the top left corner, and downloaded this as a PNG. Saved it as color-palette.png. color-palette.php reads the color-palette PNG file in and outputs a mapping between the colors used by HiRes and the C64 color byte values.
If you happen to use a different program other than HiRes, one that uses different color values, you can do the same trick. Use that other program to create a little color-palette image. Then generate the mapping using color-palette.php. Copy the mapping into png-hires-convert.php, and use that to convert a real PNG image from whatever program exports it, to a hires C64 image.
I know that some programs will export as JPEG, but I don't recommend using JPEG as an intermediate format. Because of the compression, it will not cleanly contain only 16 colors. it will contain all sorts of shades as a result of compression artifacts. PNG or GIF should be fine.
If the source is GIF, you should be able to convert that to a PNG without losing anything, using just about anything. Even the built in Preview for macOS should work. Then make sure to grab the palette numbers, as such a conversion is bound to modify the exact color values.
The hi-res image format output is in Hi-Eddy format.
9002 bytes total
- 2 byte load header: $00 $20 (little endian for $2000).
- 8000 bytes of bitmap data (set bit uses foreground color, unset uses background color)
- 1000 bytes of color data (upper 4 bits foreground color, lower 4 bits background color)