GAMMA

Arduino Library for the GAMMA function to adjust brightness of LED's etc.

Description

This library is provides a gamma lookup class. It is typical used to change the intensity / brightness of a LED to match the human eye. When a LED is given 50% PWM it looks far brighter for the eye.

This lib provides a balance between an expensive math function and the speed of a lookup table.

The accuracy of the library depends on the size of the internal array. A size of 256 is the reference. Smaller arrays use interpolation and these interpolated values are good (< 1%) down to internal array size 16. The size can be as small as 2 which is pretty inaccurate. In this latter case the curve is approximated by only two linear interpolations. In short, choose the size that fits your application.

The library has a setGamma(float gamma) function that allows an application to change the gamma value runtime. This allows adjustments that a fixed table does not have.

The class can be used to dump the internal table e.g. to place in PROGMEM.

Note: tested on UNO and ESP32 only.

Interface

Core functions

GAMMA(uint16_t size = 32) constructor, gets the size of the internal array as parameter. The default for size = 32 as this is a good balance between performance and size of the internal array. The size parameter must be in {2, 4, 8, 16, 32, 64, 128, 256 }.
begin() The array is initialized with a gamma == 2.8 which is an often used value.
begin() must be called before any other function.
setGamma(float gamma) calculates and fills the array with new values. This can be done runtime so runtime adjustment of gamma mapping.
This function takes relative quite some time. The parameter gamma must be > 0. The value 1 gives an 1:1 mapping.
getGamma() returns the set gamma value.
operator [] allows the GAMMA object to be accessed as an array. like x = G[40]; Makes it easy to switch with a real array.

Development functions

size() returns size of the internal array.
distinct() returns the number of distinct values in the table. Especially with larger internal tables this will happen.
dump() dumps the internal table to Serial. Can be useful to create an array in RAM, PROGMEM or wherever.

Operation

See example

Future ideas

test other platforms
improve documentation
look for optimizations
uint16 version?

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