Image Editor/Converter for the Adafruit GFX Library
try it out here: https://rawgit.com/Holger-Will/gfxbmp/master/editor.html
gfxbmp is an image converter with live preview. it converts color images to greyscale and greyscale to black an white images.
main features are multible options for converting to greyscale like luminance or color channel etc.
besides brightness contrast and cutoff, you can also choose from ten different dithering algorithms.
uses web-midi to allow you to controll contrast/brightness with real world buttons.
it works quite well, but is still very rough around the edges. i consider it early beta stage. Code quality is pretty low currently, sorry ;-)