Kch RGBW Calc

Calculate composite LED color from brightness of primary LEDs, vice versa.

It is a sample node command line script using kch-rgbw-lib.

Usage

calc [options] : Composite LED calculator based on kch-rgbw-lib.

getcolor [options] p1,...,pn : Synthesize composite color from comma-separated list of PWM values.

getpwm [options] (color parameters) : Compute LED PWM (alpha values) to synthesize given comma-separated color.

Run (command) -h to see help messages. getcolor and getpwm are part of calc.

Options

• -f, --file <path>
  Read LED information from JSON file (default: use typical R-G-B LEDs.)
• -n, --normalize
  Normalize PWM to [0,1] when any of alpha > 1
• -M, --max
  Compute maximum luminance at given color.
• -c, --color <CSpaceTypes>
  Use specified color space (default: 'xyY')
• -l, --list : List all LEDs in 'xyY' format
• -v, --verbose : Verbose messages
• -h, --help : Display help for command

Color space and range of color parameters are:

• -c rgb : in RGB (0-1, 0-1, 0-1)
• -c hsv : in HSV (0-360, 0-1, 0-1)
• -c XYZ : in XYZ (0-, 0-, 0-)
• -c xyY : in CIE1931 + Y (0-0.73, 0-0.83, 0-)

Installation

npm install kch-rgbw-calc

Examples

1. List default R-G-B LEDs.

These programs have default R-G-B LEDs set. If you don't provide a JSON file by -f option, the default LEDs are used. Find example of the JSON file in rgbw-led-01.json.

> getpwm -l
LEDs used in this program are
[
  LEDChip {
    _type: 'xyY',
    _a: [ 0.6857, 0.3143, 30.6 ],
    ... (omit)
]

2. PWM values to produce 6500K white at maximum luminance using the default R-G-B LEDs.

6500K white in CIE1931 chromaticity is (0.3155, 0.3270).

> getpwm 0.3155,0.3270,1 -M
Output PWM values: 0.9362416831504904,1,0.9816423115080402

If omitting -M, you get this.

> getpwm 0.3155,0.3270,1
Output PWM values: 0.009011121637358305,0.009624781506240486,0.00944809276554575

It's PWM for luminance = 1.

3. Composite color when turning all default LED at maximum brightness

> getcolor 1,1,1
Output composite color: {"_type":"xyY","_a":[0.32124386658937365,0.3247792103347052,106.00000000000001]}

If you want to get this in RGB,

> getcolor 1,1,1 -c rgb
Output composite color: {"_type":"rgb","_a":[0.9999999999999999,0.9999999999999999,0.9999999999999999]}

Unfortunately, it's inaccurate and saturated. This happens because these programs (and kch-rgbw-lib) use 'xyY' color space as their basic color representation. 'xyY' treats Y component as luminance, which is absolute value, while 'rgb' and 'hsv' spaces based on brightness, which is relative to max luminance.

The problem is that 'max luminance' is not uniform across the gamut of different LEDs, because we cannot assume that LEDs always have balanced max luminance. It is problematic in case of composite LEDs. To avoid this issue, I recommend you to use 'xyY' instead of 'rgb'.

But you probably still need to convert between RGB. Try smaller PWM values. Since max luminance was 106 for PWM=1.0, we try 0.001.

> getcolor 0.001,0.001,0.001 -c rgb
Output composite color: {"_type":"rgb","_a":[0.3799334439841642,0.3525921606511399,0.3596477933688514]}

Yes, it's white slightly shifted to red.

4. Solve PWM values for R-G-B-CW-WW LEDs

Sample JSON file has 5 LEDs: red, green, blue, cool white (6500 K) and warm white (3300 K). To obtain natural white (usually around 4000 K, which is 0.3827, 0.3820):

> getpwm -f rgbw-led-01.json 0.3827,0.3820,40
Output PWM values: 0.19421024010055238,0.19796334330569254,0,0.5188507495694974,0

We use 40 as luminance here. If we increase it to 80:

> getpwm -f rgbw-led-01.json 0.3827,0.3820,80
Output PWM values: 0.3989828893365667,0.41183560358941984,0.014118417694150506,1,0

License

The MIT License (MIT) Copyright (c) K. Chinzei ([e-mail]) Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions: The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software. THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.