Clue display color issue

[jmaloney]

My Clue is not displaying RGB565 colors correctly. The symptoms seem similar to the those reported by others back in August. The basic, saturated colors display correctly, but gradients do not. When I draw simple color ramps for R, G, and B they go from zero to full brightness in just three or four steps.

Is there a known work-around for this issue? I believe I'm using the latest Adafruit GFX and ST7789 libraries.

Let me know if there a test program you want me to run. I ran one named "clue_color_test.UF2" that shows six rectangles (red, green, blue, cyan, yellow, and magenta). That works as expected but since it doesn't exercise the low and middle brightness ranges, it doesn't actually test the problem part of the color space. I also ran one (from unawoo, I think it was) called "CLUE_COLOR_RECT.UF2". I'm guessing that the expected behavior is to show gradually increasing red, green, and blue ramps but on my Clue it displays:

IMG_2819.JPG (640.85 KiB) Viewed 349 times

[jmaloney]

I added this code to my Arduino TFT initialization (based on information from the thread started by unawoo in August):

Code: Select all

	// fix for display gamma glitch on some Clue boards:
	uint8_t gamma = 2;
	tft.sendCommand(0x26, &gamma, 1);

and that seems to have fixed the issue. Gamma settings of 2 or 4 both work but I think 2 might be slightly better (more gradual).

[adafruit_support_carter]

Try the four UF2 test examples available here:
viewtopic.php?f=65&t=168145&hilit=clue&start=45#p825094
and report back what happens.

[jmaloney]

The images look exactly like the ones posted by margor on Sat Aug 22, 2020 1:55 pm (viewtopic.php?f=65&t=168145&hilit=clue&start=60#p825486) and also fit the descriptions from unawoo earlier in that thread.

Is this a hardware or software issue? Or perhaps it's a variation between controller chips?

As mentioned, I seem to be able to work around it.

[kevinjwalters]

Do you know what colour the tab was on the clear plastic manufacturer's screen protector? I spotted some misbehaving ones have a blue tab...

[jmaloney]

Yes, mine has a dark-blue tab. (I have not yet removed the protective film from the screen so the tab is still on it.)

I live in the US (Boston area) so it would be easy to send mine back for an exchange if you'd like to study it. FWIW, a colleague in Spain has a Clue with the exact same behavior. I can ask him what color tab he has.

[kevinjwalters]

Interesting, perhaps the moral of the story is to always choose the red tab.

I'm sure @adafruit_support_carter will address the return for analysis question - Adafruit may already have one from the discussion earlier in the year.

[jmaloney]

My colleague in Spain also has a blue tab on his Clue, and he is seeing the same display issues.

it may be that the default value of the gamma register in the controller chip is different for displays from different batches or suppliers.

As I mentioned earlier, there seems to be a two-line software workaround for this issue. It might make sense to just add that fix to the Adafruit graphics library for this display.

@adafruit_support_carter I'm happy to send my Clue back for an exchange if that is helpful in debugging this.