color

Documentation

Overview

Package color implements a basic color library.

Index

• Variables
• func RGBToYCbCr(r, g, b uint8) (uint8, uint8, uint8)
• func YCbCrToRGB(y, cb, cr uint8) (uint8, uint8, uint8)
• type Alpha
  • func (c Alpha) RGBA() (r, g, b, a uint32)
• type Alpha16
  • func (c Alpha16) RGBA() (r, g, b, a uint32)
• type Color
• type Gray
  • func (c Gray) RGBA() (r, g, b, a uint32)
• type Gray16
  • func (c Gray16) RGBA() (r, g, b, a uint32)
• type Model
  • func ModelFunc(f func(Color) Color) Model
• type NRGBA
  • func (c NRGBA) RGBA() (r, g, b, a uint32)
• type NRGBA64
  • func (c NRGBA64) RGBA() (r, g, b, a uint32)
• type Palette
  • func (p Palette) Convert(c Color) Color
  • func (p Palette) Index(c Color) int
• type RGBA
  • func (c RGBA) RGBA() (r, g, b, a uint32)
• type RGBA64
  • func (c RGBA64) RGBA() (r, g, b, a uint32)
• type YCbCr
  • func (c YCbCr) RGBA() (uint32, uint32, uint32, uint32)

Variables

var (
	Black       = Gray16{0}
	White       = Gray16{0xffff}
	Transparent = Alpha16{0}
	Opaque      = Alpha16{0xffff}
)

Standard colors.

Functions

func RGBToYCbCr

func RGBToYCbCr(r, g, b uint8) (uint8, uint8, uint8)

RGBToYCbCr converts an RGB triple to a Y'CbCr triple.

func YCbCrToRGB

func YCbCrToRGB(y, cb, cr uint8) (uint8, uint8, uint8)

YCbCrToRGB converts a Y'CbCr triple to an RGB triple.

Types

type Alpha

type Alpha struct {
	A uint8
}

Alpha represents an 8-bit alpha color.

func (Alpha) RGBA

func (c Alpha) RGBA() (r, g, b, a uint32)

type Alpha16

type Alpha16 struct {
	A uint16
}

Alpha16 represents a 16-bit alpha color.

func (Alpha16) RGBA

func (c Alpha16) RGBA() (r, g, b, a uint32)

type Color

type Color interface {
	// RGBA returns the alpha-premultiplied red, green, blue and alpha values
	// for the color. Each value ranges within [0, 0xFFFF], but is represented
	// by a uint32 so that multiplying by a blend factor up to 0xFFFF will not
	// overflow.
	RGBA() (r, g, b, a uint32)
}

Color can convert itself to alpha-premultiplied 16-bits per channel RGBA. The conversion may be lossy.

type Gray

type Gray struct {
	Y uint8
}

Gray represents an 8-bit grayscale color.

func (Gray) RGBA

func (c Gray) RGBA() (r, g, b, a uint32)

type Gray16

type Gray16 struct {
	Y uint16
}

Gray16 represents a 16-bit grayscale color.

func (Gray16) RGBA

func (c Gray16) RGBA() (r, g, b, a uint32)

type Model

type Model interface {
	Convert(c Color) Color
}

Model can convert any Color to one from its own color model. The conversion may be lossy.

var (
	RGBAModel    Model = ModelFunc(rgbaModel)
	RGBA64Model  Model = ModelFunc(rgba64Model)
	NRGBAModel   Model = ModelFunc(nrgbaModel)
	NRGBA64Model Model = ModelFunc(nrgba64Model)
	AlphaModel   Model = ModelFunc(alphaModel)
	Alpha16Model Model = ModelFunc(alpha16Model)
	GrayModel    Model = ModelFunc(grayModel)
	Gray16Model  Model = ModelFunc(gray16Model)
)

Models for the standard color types.

var YCbCrModel Model = ModelFunc(yCbCrModel)

YCbCrModel is the Model for Y'CbCr colors.

func ModelFunc

func ModelFunc(f func(Color) Color) Model

ModelFunc returns a Model that invokes f to implement the conversion.

type NRGBA

type NRGBA struct {
	R, G, B, A uint8
}

NRGBA represents a non-alpha-premultiplied 32-bit color.

func (NRGBA) RGBA

func (c NRGBA) RGBA() (r, g, b, a uint32)

type NRGBA64

type NRGBA64 struct {
	R, G, B, A uint16
}

NRGBA64 represents a non-alpha-premultiplied 64-bit color, having 16 bits for each of red, green, blue and alpha.

func (NRGBA64) RGBA

func (c NRGBA64) RGBA() (r, g, b, a uint32)

type Palette

type Palette []Color

Palette is a palette of colors.

func (Palette) Convert

func (p Palette) Convert(c Color) Color

Convert returns the palette color closest to c in Euclidean R,G,B space.

func (Palette) Index

func (p Palette) Index(c Color) int

Index returns the index of the palette color closest to c in Euclidean R,G,B space.

type RGBA

type RGBA struct {
	R, G, B, A uint8
}

RGBA represents a traditional 32-bit alpha-premultiplied color, having 8 bits for each of red, green, blue and alpha.

func (RGBA) RGBA

func (c RGBA) RGBA() (r, g, b, a uint32)

type RGBA64

type RGBA64 struct {
	R, G, B, A uint16
}

RGBA64 represents a 64-bit alpha-premultiplied color, having 16 bits for each of red, green, blue and alpha.

func (RGBA64) RGBA

func (c RGBA64) RGBA() (r, g, b, a uint32)

type YCbCr

type YCbCr struct {
	Y, Cb, Cr uint8
}

YCbCr represents a fully opaque 24-bit Y'CbCr color, having 8 bits each for one luma and two chroma components.

JPEG, VP8, the MPEG family and other codecs use this color model. Such codecs often use the terms YUV and Y'CbCr interchangeably, but strictly speaking, the term YUV applies only to analog video signals, and Y' (luma) is Y (luminance) after applying gamma correction.

Conversion between RGB and Y'CbCr is lossy and there are multiple, slightly different formulae for converting between the two. This package follows the JFIF specification at http://www.w3.org/Graphics/JPEG/jfif3.pdf.

func (YCbCr) RGBA

func (c YCbCr) RGBA() (uint32, uint32, uint32, uint32)