#Chr Format

The chr image file format contains a series of bits equivalent to pixels for each tile in the spreadsheet of a rom.

A chr tile is 8x8 pixels, the data for each tile is made up of 128 bits, where the first 64 bits are the first color, the next 64 bits the second color, and where the colors overlap result in the third color, for a total of 4 colors including the background.

#tgachr

Convert a tga file, to a series of chr tiles.

uxncli tgachr.rom tgachr/test.tga # will make file tgachr/test.tga.chr

#viewer

A graphical chr viewer. Press A to invert colors, press B to toggle icn/chr modes, press arrows to resize canvas.

uxnemu viewer.rom image20x10.chr # will display the image as a 20x10 spritesheet

#chr2bmp

Converts an image in chr format to bmp.

Note: on Plan 9 the executable is called chr2img since it output a standard Plan 9 image instead of BMP.

To build on Linux:

git clone https://git.sr.ht/~rabbits/chr-format
cd chr-format
./build.sh

This creates bin/chr2bmp, which can be used by supplying a chr file on stdin and redirecting stdout to the new BMP file.

To convert a monochrome image:

chr2bmp -1 <image.bit >image.bmp

To convert a 4-color image:

chr2bmp -2 <image.chr >image.bmp

#Usage notes

For example:

bin/chr2bmp -i -w 32 < ../uxn/projects/pictures/ergo100x0c0.bit > ergo.bmp

Here, Uxn's repository has also been cloned in the parent directory, so we can use one of its example pictures.

chr files are raw data, so they do not store the color depth, the width and height, or the palette, so you need to supply these bits of information or use chr2bmp's defaults.

-w provides the width in tiles and chr2bmp will work out the height automatically, unless you also give it the height in tiles with -h. The default width is 44, which is the width that noodle starts with on Uxn's standard screen size.

-1 and -2 control the color depth. The default is -1, aligned with what noodle uses.

-i inverts the image. The default is for pixels of color zero to be white and one is black, again to match noodle.

To convert to other image formats like PNG, you can pipe the output through ImageMagick's convert tool:

bin/chr2bmp < ../uxn/untitled.bit | convert - untitled.png