User Manual

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In the DotStar library,

hue

is expressed as a 16-bit

number. Starting from 0 for red, this increments first

toward yellow (around 65536/6, or 10922 give or take a

bit), and on through green, cyan (at the halfway point of

32768), blue, magenta and back to red. In your own

code, you can allow any hue-related variables to

overflow

underflow

and they’ll “wrap around” and do

the correct and expected thing, it’s really nice.

Saturation

determines the intensity or purity of the

color…this is an 8-bit number ranging from 0 (no

saturation, just grayscale) to 255 (maximum saturation,

pure hue). In the middle, you’ll start to get sort of pastel

tones.

Value

determines the brightness of a color…it’s also an

8-bit number ranging from 0 (black, regardless of hue or

saturation) to 255 (maximum brightness).

setPixelColor() and fill() both still want RGB values though, so we convert to these from HSV by using the ColorHSV()

function:

If you just want a “pure color” (fully saturated and full brightness), the latter two arguments can be left off:

In either case, the resulting RGB value can then be passed to a pixel-setting function, e.g.:

There is

corresponding function to go the other way, from RGB to HSV. This is on purpose and by design, because

conversion in that direction is often ambiguous — there may be multiple valid possibilities for a given input. If you look

at some of the example sketches you’ll see they

keep track of their own hues

…they

don’t

assign colors to pixels and

then try to read them back out again.

…and Gamma Correction

Something you might observe when working with more nuanced color changes is that things may appear overly bright

or washed-out. It’s generally not a problem with simple primary and secondary colors, but becomes more an issue with

blends, transitions, and the sorts of pastel colors you might get from the ColorHSV() function.

Numerically

the color

values are correct, but

perceptually

our eyes make something different of it, as explained in this

guide (https://adafru.it/w2B).

The gamma32() function takes a packed RGB value (as you might get out of Color() or ColorHSV()) and filters the result

to look more perceptually correct.

uint32_t rgbcolor = strip.ColorHSV(hue, saturation, value);

uint32_t rgbcolor = strip.ColorHSV(hue);

strip.fill(rgbcolor);