Documentation
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Overview ¶
Package palette provides colours and colour sequences for charts.
The default qualitative sequence is Okabe-Ito, which is designed to remain distinguishable under the common forms of colour vision deficiency. Charts should also encode series redundantly (dash patterns, marker shapes) — colour alone is never sufficient — but starting from a safe palette costs nothing.
Index ¶
Constants ¶
This section is empty.
Variables ¶
var ( Blue = ir.RGB(0x00, 0x72, 0xB2) Orange = ir.RGB(0xE6, 0x9F, 0x00) SkyBlue = ir.RGB(0x56, 0xB4, 0xE9) Green = ir.RGB(0x00, 0x9E, 0x73) Yellow = ir.RGB(0xF0, 0xE4, 0x42) Vermilion = ir.RGB(0xD5, 0x5E, 0x00) Purple = ir.RGB(0xCC, 0x79, 0xA7) Black = ir.RGB(0x00, 0x00, 0x00) White = ir.RGB(0xFF, 0xFF, 0xFF) Red = ir.RGB(0xD5, 0x5E, 0x00) Gray = ir.RGB(0x88, 0x88, 0x88) )
Named colours used by the examples and the default theme.
var BlueOrange = Ramp{ ir.RGB(0x05, 0x30, 0x61), Blue, ir.RGB(0x92, 0xC5, 0xDE), ir.RGB(0xF2, 0xF2, 0xF2), ir.RGB(0xF4, 0xA5, 0x82), Vermilion, ir.RGB(0x7F, 0x27, 0x04), }
BlueOrange is the default diverging ramp: blue at one end, vermilion at the other, a near-neutral light grey in the middle.
Blue against orange is the one hue contrast that survives every common form of colour vision deficiency, which is why both ends are taken from Okabe-Ito rather than from the red/green pairing diverging ramps usually reach for.
var Blues = Ramp{ ir.RGB(0xF7, 0xFB, 0xFF), ir.RGB(0xDE, 0xEB, 0xF7), ir.RGB(0xC6, 0xDB, 0xEF), ir.RGB(0x9E, 0xCA, 0xE1), ir.RGB(0x6B, 0xAE, 0xD6), ir.RGB(0x42, 0x92, 0xC6), ir.RGB(0x21, 0x71, 0xB5), ir.RGB(0x08, 0x51, 0x9C), ir.RGB(0x08, 0x30, 0x6B), }
Blues is a single-hue sequential ramp, light to dark. Use it when the chart already carries a hue meaning and a second one would compete.
ColorBrewer 2.0, Brewer & Harrower.
var Cividis = Ramp{ ir.RGB(0x00, 0x20, 0x4D), ir.RGB(0x00, 0x30, 0x6F), ir.RGB(0x39, 0x48, 0x6B), ir.RGB(0x57, 0x5D, 0x6D), ir.RGB(0x70, 0x71, 0x73), ir.RGB(0x8A, 0x87, 0x79), ir.RGB(0xA6, 0x9D, 0x75), ir.RGB(0xC4, 0xB5, 0x6C), ir.RGB(0xE4, 0xCF, 0x5B), ir.RGB(0xFF, 0xEA, 0x46), }
Cividis is a sequential ramp optimised so that readers with and without deuteranomaly see the same ordering of colours, not merely a distinguishable one.
Nuñez, Anderton & Renslow, "Optimizing colormaps with consideration for color vision deficiency" (PLOS ONE, 2018).
var Default = OkabeIto
Default is the palette refract uses when a theme does not override it.
var DefaultRamp = Viridis
DefaultRamp is the sequential ramp a colour scale uses when none is given.
var Greys = Ramp{ ir.RGB(0xF7, 0xF7, 0xF7), ir.RGB(0xD9, 0xD9, 0xD9), ir.RGB(0xBD, 0xBD, 0xBD), ir.RGB(0x96, 0x96, 0x96), ir.RGB(0x73, 0x73, 0x73), ir.RGB(0x52, 0x52, 0x52), ir.RGB(0x25, 0x25, 0x25), }
Greys is a neutral sequential ramp, light to dark.
var Magma = Ramp{ ir.RGB(0x00, 0x00, 0x04), ir.RGB(0x18, 0x0F, 0x3D), ir.RGB(0x44, 0x0F, 0x76), ir.RGB(0x72, 0x1F, 0x81), ir.RGB(0x9E, 0x2F, 0x7F), ir.RGB(0xCD, 0x40, 0x71), ir.RGB(0xF1, 0x60, 0x5D), ir.RGB(0xFD, 0x96, 0x68), ir.RGB(0xFE, 0xC9, 0x8D), ir.RGB(0xFC, 0xFD, 0xBF), }
Magma is a sequential ramp from black through purple and red to near-white. Like Viridis it is perceptually uniform and monotone in lightness.
var OkabeIto = Qualitative{ Blue, Vermilion, Green, Yellow, SkyBlue, Orange, Purple, ir.RGB(0x00, 0x00, 0x00), }
OkabeIto is the default colourblind-safe qualitative palette.
Okabe & Ito, "Color Universal Design" (2008).
var PurpleGreen = Ramp{ ir.RGB(0x40, 0x00, 0x4B), ir.RGB(0x9A, 0x70, 0xAB), ir.RGB(0xE7, 0xD4, 0xE8), ir.RGB(0xF7, 0xF7, 0xF7), ir.RGB(0xD9, 0xF0, 0xD3), ir.RGB(0x5A, 0xAE, 0x61), ir.RGB(0x00, 0x44, 0x1B), }
PurpleGreen is a second diverging ramp, for when a chart already spends blue or orange on something else. Purple against green is the next safest pairing after blue against orange.
var Viridis = Ramp{ ir.RGB(0x44, 0x01, 0x54), ir.RGB(0x48, 0x28, 0x78), ir.RGB(0x3E, 0x4A, 0x89), ir.RGB(0x31, 0x68, 0x8E), ir.RGB(0x26, 0x82, 0x8E), ir.RGB(0x1F, 0x9E, 0x89), ir.RGB(0x35, 0xB7, 0x79), ir.RGB(0x6D, 0xCD, 0x59), ir.RGB(0xB4, 0xDE, 0x2C), ir.RGB(0xFD, 0xE7, 0x25), }
Viridis is the default sequential ramp: perceptually uniform, monotone in lightness — so it survives being printed in greyscale — and legible under every common form of colour vision deficiency.
Smith & van der Walt, matplotlib (2015).
Functions ¶
func Lerp ¶ added in v0.2.0
Lerp blends a into b by t in [0, 1], interpolating the colour channels in linear light and the alpha channel directly.
Alpha is not gamma-encoded, so it interpolates as it is. The colours are non-premultiplied, which means blending two colours of different alpha interpolates the *stated* colour rather than the composited one — for a colour ramp, where the anchors are normally opaque, that is what a caller expects.
Types ¶
type Qualitative ¶
Qualitative is a sequence of categorical colours.
type Ramp ¶ added in v0.2.0
Ramp is a continuous colour ramp: anchor colours spaced evenly over [0, 1] and interpolated between.
Interpolation happens in linear light, not in sRGB byte space. Averaging two gamma-encoded bytes darkens the midpoint of a ramp by roughly 20% — a band that reads as a seam across an otherwise smooth gradient. gg composites in linear space for the same reason, so a ramp evaluated here and a gradient rasterised there agree.
func (Ramp) At ¶ added in v0.2.0
At returns the colour at position t, clamped to [0, 1]. An empty Ramp returns ir.Transparent; a one-colour Ramp is constant.
Source Files