ledmatrix: gamma correction for smoother brightness ramps #99
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This costs ~256 bytes of flash (once referenced). I've tried to keep the generated code readable.
The brightness values sent to the LED controller actually control a PWM duty cycle. LEDs emit light roughly in proportion to the PWM duty cycle, but human vision perceives brightness on an exponential curve -- generally it takes 2x the physical luminous flux for the eye to perceive something as one step brighter. As a result, brightness ramps (like the one generated by --all-brightnesses) were rapidly brightening to what appeared to be max, and then flattening. This change adds gamma correction, which maps the linear input brightness values to a non-linear function of PWM duty cycles, causing the ramp to look far more ramp-y. The gamma value I've chosen here is arguably a preference, I messed with output on a PVT panel until I found something that looked approximately right.
|
FWIW, I'm not at all sure that I hooked the gamma correction at the right points in the code --- definitely open to guidance if you'd like it moved! |
|
It's also worth calling out that gamma correction makes all mid-range brightnesses look dimmer (by design!). So it might be good to increase the default brightness multiplier (currently 51 on PVT looks like?) to something higher. I'm happy to find a value that matches the approximate intensity of the original firmware if you'd like. |
|
This change reminds me of what FastLED does. Great idea and work. Can I use this code in my fork of the repo? |
|
Would appreciate progress on this change! I also noticed this issue. |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
The brightness values sent to the LED controller actually control a PWM
duty cycle. LEDs emit light roughly in proportion to the PWM duty cycle,
but human vision perceives brightness on an exponential curve --
generally it takes 2x the physical luminous flux for the eye to perceive
something as one step brighter.
As a result, brightness ramps (like the one generated by
--all-brightnesses) were rapidly brightening to what appeared to be max,
and then flattening.
This change adds gamma correction, which maps the linear input
brightness values to a non-linear function of PWM duty cycles, causing
the ramp to look far more ramp-y.
The gamma value I've chosen here is arguably a preference, I messed with
output on a PVT panel until I found something that looked approximately
right.
Photo of a panel with the firmware from
main(left) vs this change (right):