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Color artifacts on display (SPI+18-bit RGB) using ST7701s driver

Senior III


I'm getting 2 round displays up and running using tGFX on an STM32F767 (custom board, external SDRAM and QSPI)

I think almost everything is running but I have some weird artifacts. the clearest I can show is the color wheel test.

While the image is 24-bit and the display is 18-bit I wonder why I see the clear lines across the display (Please disregard the red stripe horisontally - that's a smudge on the protective film)

To me it would seem like something like a rounding of the color information but that would make much more sense if I was coming from less than 18-bit.

Anyone who can offer some insights here or point me in a direction? I tried with a real image and certain colors just get REALLY wonky..


It's great to hear that you're working on getting those round displays up and running with tGFX on your custom STM32F767 board. Those color artifacts can be a bit puzzling, but I might have an idea.

The fact that you're dealing with a 24-bit image and an 18-bit display could indeed be a source of the problem. When you're converting from 24-bit to 18-bit, there's potential for rounding errors in color representation, which might result in those lines you're seeing.

To tackle this, you might want to consider using a dithering algorithm during the conversion process. Dithering can help smooth out color transitions, reducing the likelihood of artifacts. It's a common technique used when displaying high-color images on lower-color screens.

And just a fun sidenote, if you're into graphics and colors, you might find PikaShow pretty interesting. It's a show that's all about exploring and celebrating the world of colors and visuals. It could provide you with some cool inspiration for your display project!

Hope this helps, and best of luck with your display project!!