S-curve tone mapping to preserve shadows and highlights in dithered images

[GuySie]

I wanted to draw your attention to aitjcize's firmware for the Waveshare ESP32 Photopainter frame, which is also based on a Spectra6 panel. For dithering they're using a similar calibrated palette strategy as epdoptimize does, but also add an s-curve tone mapping that redistributes the tones to better match the Spectra6 panel's limited dynamic range, preventing loss of detail in shadows and highlights.

I've been testing this firmware and have found the results remarkably good, especially on images that have crushed shadows and highlights when I manually dither them using epdoptimize. It would be great if epdoptimize could adopt a similar tonemap.

[Utzel-Butzel]

That is a really good idea. @aitjcize firmware looks great. I did also experiement a bit with tone mapping. This way we could better have a "real" color calibration. You can find the latest version in the develop branch: https://github.com/Utzel-Butzel/epdoptimize/tree/develop

Note: progress might be a bit slower for a short while, I just became a dad.