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126 lines
4.3 KiB
Markdown
126 lines
4.3 KiB
Markdown
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[](https://github.com/marketplace/actions/arduino_ci)
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[](https://github.com/RobTillaart/Kelvin2RGB/actions/workflows/arduino-lint.yml)
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[](https://github.com/RobTillaart/Kelvin2RGB/actions/workflows/jsoncheck.yml)
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[](https://github.com/RobTillaart/Kelvin2RGB/blob/master/LICENSE)
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[](https://github.com/RobTillaart/Kelvin2RGB/releases)
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# Kelvin2RGB
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Arduino library for converting temperature and brightness to RGB values.
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## Credentials
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This library is based upon an article of Tanner Helland and a related story by Neil Bartlett
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- http://www.tannerhelland.com/4435/convert-temperature-rgb-algorithm-code/
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- http://www.zombieprototypes.com/?p=210
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- https://en.wikipedia.org/wiki/Color_temperature#Categorizing_different_lighting
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There are more approximation formulas, some claim to be better,
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however these are not investigated. On request these can be added.
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## Description
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The library converts a temperature in Kelvin and a brightness (0..100%)
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to three numbers **red**, **green** and **blue**.
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These numbers are weights can be used to correct a colour image for virtual white temperature.
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There are two convert functions where the **convert_NB()** is claimed to be
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the more accurate one.
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With the numbers **red**, **green** and **blue** calculated one can convert images
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so they will look more like taken with candle light, sunrise or sunset etc.
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**pseudo code**
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```cpp
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Kelvin2RGB KRGB;
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KRGB.convert(1850, 100); // sunrise light factors
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for each pixel in image
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{
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red *= KRGB.red();
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green *= KRGB.green();
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blue *= KRGB.blue();
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drawPixel();
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}
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```
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The numbers can also be used to reduce the blue channel so it has less effect
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on "getting sleepy".
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The library uses floats for the R,G and B weights to keep values as accurate as possible.
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Especially with images with more than 8 bits per channel this is preferred.
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That said it is also possible to use this on a 565 image or to adjust colour lookup tables.
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## Interface
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```cpp
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#include "Kelvin2RGB.h"
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```
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The interface is straightforward:
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- **Kelvin2RGB()** constructor
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- **void begin()** empty function for now.
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- **void reset()** resets all internal values to 0.
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All colours, brightness and temperature.
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- **void convert_TH(float temperature, float brightness = 100)**
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temperature = 0..65500 temperature below 1000 is not well defined.
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brightness = 0..100%,
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- **void convert_NB(float temperature, float brightness = 100)**
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temperature = 0..65500 temperature below 1000 is not well defined.
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brightness = 0..100%,
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Is a bit more accurate and slightly slower (few %). Read link above for more information.
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- **float temperature()** returns temperature, to check the value used.
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- **float brightness()** returns brightness, to check the value used.
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- **float red()** returns red channel weight 0.0 .. 1.0
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note this is different from Helland / Bartlett who both use an integer value 0 .. 255
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- **float green()** returns green channel weight 0.0 .. 1.0
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- **float blue()** returns blue channel weight 0.0 .. 1.0
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- **uint32_t setRGB(float red, float green, float blue, float brightness = 100)** sets RGB values
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red, green, blue should be in 0 .. 1.0 range. brightness should be in 0..100%, Default = 100%.
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returns a 24 bit RGB value,
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- **uint32_t RGB()** returns a 24 bit RGB value, 0 .. 16777215
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more efficient than 3 floats for communication.
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- **uint16_t RGB565()** returns a 16 bit RGB value, 5 bits for red, 6 for green and 5 for blue.
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- **uint32_t BGR()** returns a 24 bit BGR value, 0 .. 16777215
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- **uint32_t CMYK()** returns a 32 bit = 4 byte CMYK value,
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## Operations
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See examples
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## Future
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#### Must
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#### Should
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- define constants like candleLight as parameter.
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- investigate other formulas.
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- investigate usability for RGB led strip.
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#### Could
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- separate brightness per colour channel to mimic "artificial illumination" (0.2.0 ?)
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- remove begin() ?
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- add examples
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- ledstrip
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- CMYK()
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- BGR()
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#### Wont
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- investigate **RGB_10_12_10()**
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- nowhere used (not found)
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