4-bit color (NOT gray/grey scale) image/bitmap best practices - is it possible?

[clach04]

I have some CYD devices (both CYD1 and CYD2) as described by project https://github.com/witnessmenow/ESP32-Cheap-Yellow-Display/

I put together a working show fullscreen image test/demos. It's working but the nano-gui demo one could do with more work, possibly documentation related.

I have a 16-bit demo (NOT using nano-gui) in https://github.com/clach04/cyd_clocks/blob/main/bitmap_fullscreen.py which works well with demo images (once converted using https://github.com/rdagger/micropython-ili9341/blob/master/utils/img2rgb565.py) in https://github.com/clach04/cyd_clocks/tree/main/images, for example:

https://github.com/clach04/cyd_clocks/blob/main/images/Philips_PM5544.png

I have this working with the 8-bit driver in color https://github.com/peterhinch/micropython-nano-gui/blob/master/drivers/ili93xx/ili9341_8bit.py

I have this working with the 4-bit driver in grayscale https://github.com/peterhinch/micropython-nano-gui/blob/master/drivers/ili93xx/ili9341.py

I can not see a way to get this working in 4-bit color (out-of-box), as it looks like https://github.com/peterhinch/micropython-nano-gui/blob/master/img_cvt.py doesn't support this. Has anyone looked into this at all? I'm speculating that images could be converted into raw 4-bit color (i.e. 2 pixels per byte). And probably need some way to set/load a palette?

I think I still have enough memory to do what I want to do with 8-bit color but trying to think of backup plans 😉

[peterhinch]

4-bit color is not really feasible. You might assign them RGGB but I think the results would look awful. The driver's use of a LUT enables a fixed set of 16 colors but I can't see how to employ this for general purpose image display.

[clach04]

So I've been spending a bit of time thinking about this... and implementing some tiny POCs.

I think some use can be had out of 4-bit/16 color. It was certainly useful a few decades ago (and still today in some terminals) 😜 , I agree for the majority of use cases more colors is easier. I think for some carton and pixel art use cases it could work.

It turns out with the CYD2 device I'm playing with, I have less memory available, not enough for 8-bit color framebuffer (with I think the same firmware of MicroPython installed as my CYD1 which does not have this issue) so I've been forced to think about this some more.

I made a quick PNG (see clach04/cyd_clocks#40) using the palette defined in https://github.com/peterhinch/micropython-nano-gui/blob/master/gui/core/colors.py with the same palette (in the same index locations), with some greys thrown into positions; 12, 13, and 14
https://github.com/peterhinch/micropython-nano-gui/blob/master/gui/core/colors.py#L26

I was able to put together a super tiny pixelart demo together using that palette (and https://pydpainter.org/), in person it looks alright (it doesn't come out well in photos peterhinch/micropython-font-to-py#71 (comment)).

If I was to load a different palette at the same time as the raw bitmap it would have more options.

I don't really want to create a new image format but I may have too if I want to progress this. I was thinking about cloning the format output by img_cvt.py and adding a palette somewhere (ideally before the bitmap, after the resolution but this would be incompatible with the existing format, after might be better for that ).

I'm looking to create a Bubble Bobble clock for someone, and the existing sprites I found happen to be 4-bit so I'm optimistic I'll be able to pull something off :-)

As always, thanks for such a nice/well-documented library. Saved me a bunch of work implementing low-level stuff 😃