Arduino Library for the GAMMA function to adjust brightness of LED's etc.
This library 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 are not possible with a fixed table.
The class provides dump() to create a table e.g. to place in PROGMEM. Since 0.2.2 the library also has dumpArray() to generate a C-style array.
Note: tested on UNO and ESP32 only.
As always, feedback is welcome.
#include "gamma.h"- 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 a power of 2, so in {2, 4, 8, 16, 32, 64, 128, 256 }.
- ~GAMMA() destructor.
- bool begin() The internal lookup array is allocated and initialized with a gamma == 2.8. This is an often used value to adjust light to human eye responses. Note that begin() must be called before any other function. Returns false if allocation fails.
- bool isAllocated() returns true if the internal lookup array is allocated.
- void setGamma(float gamma) calculates and fills the internal lookup array with new values. This can be done runtime, so adjustment of gamma mapping is possible anytime. This calculation are relative expensive and takes quite some time (depending on size). If the internal array already is calculated for gamma, the calculation will be skipped. Returns false if gamma == 0 or if no array is allocated.
- float getGamma() returns the set gamma value.
- uint8_t operator [uint8_t index] allows the GAMMA object to be accessed as an array.
like
x = G[40];Makes it easy to switch with a real array. The value returned is in the range 0 .. 255, so the user may need to scale it e.g. to 0.0 - 1.0. Note: if internal array not allocated the function returns 0. As this is a legitimate value the user should take care.
The parameter gamma normally must be > 0. The value 1 gives an 1:1 mapping. Since 0.5.0 the library supports a negative value of gamma. It inverts the values returned (0..255) => (255..0). This can be useful e.g. for inverted PWM polarity.
- uint16_t size() returns the size of the internal array. This is always a power of 2.
- uint16_t distinct() returns the number of distinct values in the internal array. Especially with larger internal arrays there will be more duplicate numbers.
- bool dump(Stream *str = &Serial) dumps the internal array to a stream, default Serial. Useful to create an array in RAM, PROGMEM, EEPROM, in a file or wherever. Returns false if no array is allocated.
- void dumpArray(Stream *str = &Serial) dumps the internal array to a stream, default Serial, as a C-style array. See example. Returns false if no array is allocated.
See example.
- improve documentation
- test other platforms
- uint16 version?
- GAMMA16,
- GAMMA32,
- GAMMA_RGB ?
- look for optimizations (done in 0.4.0)
- setGamma -> pow() is expensive
- setGamma(gamma) gamma = 1.0 is linear, less math (too specific?)
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Thank you,