Wrong color from LEDs, broken gamma algorithm

[jcam]

Describe the bug
When I use the Home Assistant built in color picker, very often the bulbs turn the wrong color

Firmware:

• Versions tried: 1.18.181, 1.18.109 and 1.17.736
• Device: Daybetter 800lm RGB+2700-6500K
• Chip/model: wb2l / BK7231T
• Device config: bp5758d on pins 7 and 8, with BP5758D_Map 2 1 0 3 4

To Reproduce
Steps to reproduce the behavior:

1. Add a bulb to home assistant
2. Open the light entity for the device, choose a color on the color picker
3. Observe the color
4. Use MQTT explorer to see what color was selected, and compare that color to the light

Screenshots
Here I selected orange:

Here's the color that was sent through MQTT:

This is what color FF8402 should be:
https://www.color-hex.com/color/ff8402

This is what the light is doing. The light on the left is using ESPHome (it is dining-room-1), the light on the right is using OpenBK 1.18.181. Both are showing the same color, in theory.
If it isn't clear from the image, because photos look different on different screens, the left ESPHome bulb looks like the same orange as FF8402, while the OpenBK bulb looks greenish yellow.

Additional context
I thought maybe it was just the way these bulbs were until I tried ESPHome on this one bulb, and there the colors work perfectly. Unfortunately the startup time for ESPHome is terrible compared to OpenBK so I'd much rather stick to this project!

[jcam]

After a WHOLE LOT of digging and trying to understand what was going on, I have finally figured out that the problem is not with the BP5758D implementation, instead it is with the gamma correction.
Gamma should be applied to the final color value, not just the brightness. It shouldn't scale all three colors identically, it should scale them individually.

I'll work on a PR and some examples, but you can see how ESP calculates gamma here:
inline uint8_t color_correct_red(uint8_t red) const ESPHOME_ALWAYS_INLINE {
uint8_t res = esp_scale8(esp_scale8(red, this->max_brightness_.red), this->local_brightness_);
return to_uint8_scale(gamma_correct(res / 255.0f, gamma))
}

[jcam]

This updated gamma correction works correctly:
main...jcam:OpenBK7231T_App:fix_gamma_correction

[openshwprojects]

Interesting finding, if you can, please open PR, and I'll merge. However, maybe someone else can also check with bulbs, @divadiow @NonPIayerCharacter @MaxineMuster ?

[jcam]

I can make a draft PR, but I'd say it's not ready yet. I have a non-TuyaMCU bulb that I want to see how it reacts with just the normal 5 PWMs. Also the unit tests are failing, as expected because it's making different outputs now.

In addition I think the light output of the warm/cool white may not be quite right still. Test binaries can be found in the github actions output on my repo for now...

[divadiow]

yes. much better with gamma PR. it's kinda green with general release, nothing close to the colour I set

also, if you start typing into RGB numbers OBK currently cuts out the bulb and you have to turn it on when you're finished. With PR number changes are updated live to bulb, changing colour.

bulb tested on was PWM ESPC2 https://www.elektroda.com/rtvforum/topic4134135.html

[divadiow]

looks like build needs a tweak though https://github.com/jcam/OpenBK7231T_App/actions/runs/18247235937/job/51956846787

[jcam]

I currently don't have the minimum brightness calculation, because I don't know what it is for:

defined: float ch_bright_min = g_cfg.led_corr.rgb_bright_min / 100;
multiplied by the gamma in the old algorithm: (1 - ch_bright_min) + ch_bright_min

Do you have a reference for why it was included, or what the purpose is?

I also removed the "boost gain to get full brightness when one RGB base color is dominant" because I think the new algorithm handles colors better without it.

[jcam]

looks like build needs a tweak though https://github.com/jcam/OpenBK7231T_App/actions/runs/18247235937/job/51956846787

I've now corrected the self test and also fixed the color temperature settings.

[MaxineMuster]

... maybe someone else can also check with bulbs, @divadiow @NonPIayerCharacter @MaxineMuster ?

Sorry, I can't help here since I have no "smart" bulbs at all.

[jcam]

Resolved by #1825