# package color
`import "image/color"`
color包實現了基本色彩庫。
## Index
* [Variables](#pkg-variables)
* [type Color](#Color)
* [type Model](#Model)
* [func ModelFunc(f func(Color) Color) Model](#ModelFunc)
* [type Alpha](#Alpha)
* [func (c Alpha) RGBA() (r, g, b, a uint32)](#Alpha.RGBA)
* [type Alpha16](#Alpha16)
* [func (c Alpha16) RGBA() (r, g, b, a uint32)](#Alpha16.RGBA)
* [type Gray](#Gray)
* [func (c Gray) RGBA() (r, g, b, a uint32)](#Gray.RGBA)
* [type Gray16](#Gray16)
* [func (c Gray16) RGBA() (r, g, b, a uint32)](#Gray16.RGBA)
* [type RGBA](#RGBA)
* [func (c RGBA) RGBA() (r, g, b, a uint32)](#RGBA.RGBA)
* [type RGBA64](#RGBA64)
* [func (c RGBA64) RGBA() (r, g, b, a uint32)](#RGBA64.RGBA)
* [type NRGBA](#NRGBA)
* [func (c NRGBA) RGBA() (r, g, b, a uint32)](#NRGBA.RGBA)
* [type NRGBA64](#NRGBA64)
* [func (c NRGBA64) RGBA() (r, g, b, a uint32)](#NRGBA64.RGBA)
* [type YCbCr](#YCbCr)
* [func (c YCbCr) RGBA() (uint32, uint32, uint32, uint32)](#YCbCr.RGBA)
* [type Palette](#Palette)
* [func (p Palette) Convert(c Color) Color](#Palette.Convert)
* [func (p Palette) Index(c Color) int](#Palette.Index)
* [func RGBToYCbCr(r, g, b uint8) (uint8, uint8, uint8)](#RGBToYCbCr)
* [func YCbCrToRGB(y, cb, cr uint8) (uint8, uint8, uint8)](#YCbCrToRGB)
## Variables
```
var (
Black = Gray16{0} // 黑色
White = Gray16{0xffff} // 白色
Transparent = Alpha16{0} // 完全透明
Opaque = Alpha16{0xffff} // 完全不透明
)
```
標準色彩。
## type [Color](https://github.com/golang/go/blob/master/src/image/color/color.go#L10 "View Source")
```
type Color interface {
// 方法返回預乘了alpha的紅、綠、藍色彩值和alpha通道值，范圍都在[0, 0xFFFF]。
// 返回值類型為uint32，這樣當乘以接近0xFFFF的混合參數時，不會溢出。
RGBA() (r, g, b, a uint32)
}
```
實現了Color接口的類型可以將自身轉化為預乘了alpha的16位通道的RGBA，轉換可能會丟失色彩信息。
## type [Model](https://github.com/golang/go/blob/master/src/image/color/color.go#L133 "View Source")
```
type Model interface {
Convert(c Color) Color
}
```
Model接口可以將任意Color接口轉換為采用自身色彩模型的Color接口。轉換可能會丟失色彩信息。
```
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接口返回標準的Color接口類型。
```
var YCbCrModel Model = ModelFunc(yCbCrModel)
```
包變量YcbCrModel是Y'cbCr色彩模型的Model接口。
### func [ModelFunc](https://github.com/golang/go/blob/master/src/image/color/color.go#L138 "View Source")
```
func ModelFunc(f func(Color) Color) Model
```
函數ModelFunc返回一個調用函數f實現色彩轉換的Model接口。
## type [Alpha](https://github.com/golang/go/blob/master/src/image/color/color.go#L90 "View Source")
```
type Alpha struct {
A uint8
}
```
Alpha類型代表一個8位的alpha通道（alpha通道表示透明度）。
### func (Alpha) [RGBA](https://github.com/golang/go/blob/master/src/image/color/color.go#L94 "View Source")
```
func (c Alpha) RGBA() (r, g, b, a uint32)
```
## type [Alpha16](https://github.com/golang/go/blob/master/src/image/color/color.go#L101 "View Source")
```
type Alpha16 struct {
A uint16
}
```
Alpha16類型代表一個16位的alpha通道。
### func (Alpha16) [RGBA](https://github.com/golang/go/blob/master/src/image/color/color.go#L105 "View Source")
```
func (c Alpha16) RGBA() (r, g, b, a uint32)
```
## type [Gray](https://github.com/golang/go/blob/master/src/image/color/color.go#L111 "View Source")
```
type Gray struct {
Y uint8
}
```
Gray類型代表一個8位的灰度色彩。
### func (Gray) [RGBA](https://github.com/golang/go/blob/master/src/image/color/color.go#L115 "View Source")
```
func (c Gray) RGBA() (r, g, b, a uint32)
```
## type [Gray16](https://github.com/golang/go/blob/master/src/image/color/color.go#L122 "View Source")
```
type Gray16 struct {
Y uint16
}
```
Gray16類型代表一個16位的灰度色彩。
### func (Gray16) [RGBA](https://github.com/golang/go/blob/master/src/image/color/color.go#L126 "View Source")
```
func (c Gray16) RGBA() (r, g, b, a uint32)
```
## type [RGBA](https://github.com/golang/go/blob/master/src/image/color/color.go#L20 "View Source")
```
type RGBA struct {
R, G, B, A uint8
}
```
RGBA類型代表傳統的預乘了alpha通道的32位RGB色彩，Red、Green、Blue、Alpha各8位。
### func (RGBA) [RGBA](https://github.com/golang/go/blob/master/src/image/color/color.go#L24 "View Source")
```
func (c RGBA) RGBA() (r, g, b, a uint32)
```
## type [RGBA64](https://github.com/golang/go/blob/master/src/image/color/color.go#L38 "View Source")
```
type RGBA64 struct {
R, G, B, A uint16
}
```
RGBA64類型代表預乘了alpha通道的64位RGB色彩，Red、Green、Blue、Alpha各16位。
### func (RGBA64) [RGBA](https://github.com/golang/go/blob/master/src/image/color/color.go#L42 "View Source")
```
func (c RGBA64) RGBA() (r, g, b, a uint32)
```
## type [NRGBA](https://github.com/golang/go/blob/master/src/image/color/color.go#L47 "View Source")
```
type NRGBA struct {
R, G, B, A uint8
}
```
NRGBA類型代表沒有預乘alpha通道的32位RGB色彩，Red、Green、Blue、Alpha各8位。
### func (NRGBA) [RGBA](https://github.com/golang/go/blob/master/src/image/color/color.go#L51 "View Source")
```
func (c NRGBA) RGBA() (r, g, b, a uint32)
```
## type [NRGBA64](https://github.com/golang/go/blob/master/src/image/color/color.go#L71 "View Source")
```
type NRGBA64 struct {
R, G, B, A uint16
}
```
NRGBA64類型代表沒有預乘alpha通道的64位RGB色彩，Red、Green、Blue、Alpha各16位。
### func (NRGBA64) [RGBA](https://github.com/golang/go/blob/master/src/image/color/color.go#L75 "View Source")
```
func (c NRGBA64) RGBA() (r, g, b, a uint32)
```
## type [YCbCr](https://github.com/golang/go/blob/master/src/image/color/ycbcr.go#L80 "View Source")
```
type YCbCr struct {
Y, Cb, Cr uint8
}
```
YcbCr代表完全不透明的24位Y'CbCr色彩；每個色彩都有1個亮度成分和2個色度成分，分別用8位字節表示。
JPEG、VP8、MPEG家族和其他編碼方式使用本色彩模型。這些編碼通常將Y'CbCr?和YUV兩個色彩模型等同使用（Y=Y'=黃、U=Cb=青、V=Cr=品紅）。但嚴格來說，YUV模只用于模擬視頻信號，Y'是經過伽瑪校正的Y。RGB和Y'CbCr色彩模型之間的轉換會丟失色彩信息。兩個色彩模型之間的轉換有多個存在細微區別的算法。本包采用JFIF算法，參見[http://www.w3.org/Graphics/JPEG/jfif3.pdf](http://www.w3.org/Graphics/JPEG/jfif3.pdf)
### func (YCbCr) [RGBA](https://github.com/golang/go/blob/master/src/image/color/ycbcr.go#L84 "View Source")
```
func (c YCbCr) RGBA() (uint32, uint32, uint32, uint32)
```
## type [Palette](https://github.com/golang/go/blob/master/src/image/color/color.go#L254 "View Source")
```
type Palette []Color
```
Palette類型代表一個色彩的調色板。
### func (Palette) [Convert](https://github.com/golang/go/blob/master/src/image/color/color.go#L257 "View Source")
```
func (p Palette) Convert(c Color) Color
```
返回調色板中與色彩c在歐幾里德RGB色彩空間最接近的色彩。（實現了Model接口）
### func (Palette) [Index](https://github.com/golang/go/blob/master/src/image/color/color.go#L266 "View Source")
```
func (p Palette) Index(c Color) int
```
返回調色板中與色彩c在歐幾里德RGB色彩空間最接近的色彩的索引。
## func [RGBToYCbCr](https://github.com/golang/go/blob/master/src/image/color/ycbcr.go#L8 "View Source")
```
func RGBToYCbCr(r, g, b uint8) (uint8, uint8, uint8)
```
函數將RGB三原色轉換為Y'CbCr三原色。
## func [YCbCrToRGB](https://github.com/golang/go/blob/master/src/image/color/ycbcr.go#L39 "View Source")
```
func YCbCrToRGB(y, cb, cr uint8) (uint8, uint8, uint8)
```
函數將Y'CbCr三原色轉換為RGB三原色。
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