TouchGFX L8 Color Encoding

DWeb_2 · ‎2021-11-21

Hi,

because of RAM limitations I decided to try out the L8 color encoding, which is supported by the LTDC of my STM32H753. The basic function is working now, however not to a satisfying extent.

In the CubeIDE V 1.5.0, under TouchGFX 4.16, only 8 Bit color space (ARGB2222 etc.) is available, when using the L8 functionality:The problem with this is, that some colors look awful, and especially the anti aliasing of text is bad.

This brings me to the question, why for example L8RGB565 or L8RGB888 is not supported from TouchGFX side.

Technically, from my understanding, it does not matter, since the memory space of the color lookup table is allocated anyway (256*32Bit words).

I would really be glad to display the "true" colors (for corporate design). Limiting myself to 256 of those would not be a problem.

Am I missing a crucial setting here or is this maybe supported in more recent releases of TouchGFX/CubeIDE?

MM..1 · ‎2021-11-22

In real now L8 = CLUT 8888, but for global image and objects conversion on generating phase is coded as ARGB2222.

Table is in generated files in target and you can overide it, but then you need correct all colors and images too.

DWeb_2 · ‎2021-11-22

Thanks for your reply. I found the buffer, but I would really have headaches trying to bypass TouchGFX code generation.

MM..1 · ‎2021-11-22

Maybe you show an image or what is your trouble. ARGB2222 create gradient for base color combination and CLUT palete is completed with aplha levels. Plus converter use dithering methods usw.
When you have free flash and you need better images, you can reconfig LTDC to use both layers in hw, and place static background under part or full LCD in RGB888 quality.
This is just for LTDC controlled displays and if used , then layer 0 is your RGB888 perfect background static from flash and layer 1 is TouchGFX framebuffer in ram.

DWeb_2 · ‎2021-11-23

My problem is, that I want to use L8, but the compression messes up the colors (still recognizable, but far off due to the LSB's being cut). I'm just wondering why TouchGFX limits us to these small color spaces, when (from my knowledge) there is no such a need.

Very interesting idea, to use different layers for the LTDC, thanks!

MM..1 · ‎2021-11-23

Example on 1280x480 TouchGFX two layers