Documentation
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Overview ¶
Package webp provides an interface to libwebp library to decoding/encoding WebP image.
Index ¶
- func DecodeRGBA(data []byte, options *DecoderOptions) (img *image.RGBA, err error)
- func EncodeRGBA(w io.Writer, img image.Image, c Config) (err error)
- func EncodeYUVA(w io.Writer, img *YUVAImage, c Config) (err error)
- func GetDecoderVersion() (v int)
- func GetDestinationManagerMapLen() int
- func GetInfo(data []byte) (width, height int)
- type BitstreamFeatures
- type ColorSpace
- type Config
- type DecoderOptions
- type FilterType
- type Preset
- type YUVAImage
Constants ¶
This section is empty.
Variables ¶
This section is empty.
Functions ¶
func DecodeRGBA ¶
func DecodeRGBA(data []byte, options *DecoderOptions) (img *image.RGBA, err error)
DecodeRGBA decodes WebP image into RGBA image and returns it as an *image.RGBA.
func EncodeRGBA ¶
EncodeRGBA encodes and writes image.Image into the writer as WebP. Now supports image.RGBA or image.NRGBA.
func EncodeYUVA ¶
EncodeYUVA encodes and writes YUVA Image data into the writer as WebP.
func GetDecoderVersion ¶
func GetDecoderVersion() (v int)
GetDecoderVersion returns decoder's version number, packed in hexadecimal. e.g; v0.4.2 is 0x000402
func GetDestinationManagerMapLen ¶
func GetDestinationManagerMapLen() int
GetDestinationManagerMapLen returns the number of globally working sourceManagers for debug
Types ¶
type BitstreamFeatures ¶
type BitstreamFeatures struct {
Width int // Image width in pixels
Height int // Image height in pixles
HasAlpha bool // True if data stream contains a alpha channel.
HasAnimation bool // True if data stream is an animation
Format int // Image compression format
}
BitstreamFeatures represents the image properties which are retrived from data stream.
func GetFeatures ¶
func GetFeatures(data []byte) (f *BitstreamFeatures, err error)
GetFeatures returns features as BitstreamFeatures retrived from data stream.
type ColorSpace ¶
type ColorSpace int
ColorSpace represents encoding color space in WebP
const ( // YUV420 specifies YUV4:2:0 YUV420 ColorSpace = C.WEBP_YUV420 // YUV420A specifies YUV4:2:0 with alpha channel YUV420A ColorSpace = C.WEBP_YUV420A )
type Config ¶
type Config struct {
Preset Preset // Parameters Preset
Lossless bool // True if use lossless encoding
Quality float32 // WebP quality factor, 0-100
Method int // Quality/Speed trade-off factor, 0=faster / 6=slower-better
TargetSize int // Target size of encoded file in bytes
TargetPSNR float32 // Target PSNR, takes precedence over TargetSize
Segments int // Maximum number of segments to use, 1..4
SNSStrength int // Strength of spartial noise shaping, 0..100=maximum
FilterStrength int // Strength of filter, 0..100=strength
FilterSharpness int // Sharpness of filter, 0..7=sharpness
FilterType FilterType // Filtering type
Pass int // Number of entropy-analysis passes, 0..100
}
Config specifies WebP encoding configuration.
type DecoderOptions ¶
type DecoderOptions struct {
BypassFiltering bool // If true, bypass filtering process
NoFancyUpsampling bool // If true, do not fancy upsampling
Crop image.Rectangle // Do cropping if image.Rectangle is not empty.
Scale image.Rectangle // Do scaling if image.Rectangle is not empty.
UseThreads bool // If true, use multi threads
DitheringStrength int // Specify dithering strength [0=Off .. 100=full]
Flip bool // If true, flip output vertically
AlphaDitheringStrength int // Specify alpha dithering strength in [0..100]
}
DecoderOptions specifies decoding options of WebP.
type FilterType ¶
type FilterType int
FilterType corresponds to filter types in compression parameters.
const ( // SimpleFilter (=0, default) SimpleFilter FilterType = iota // StrongFilter (=1) StrongFilter )
type Preset ¶
type Preset int
Preset corresponds to C.WebPPreset.
const ( // PresetDefault corresponds to WEBP_PRESET_DEFAULT, for default preset. PresetDefault Preset = C.WEBP_PRESET_DEFAULT // PresetPicture corresponds to WEBP_PRESET_PICTURE, for digital picture, like portrait, inner shot PresetPicture Preset = C.WEBP_PRESET_PICTURE // PresetPhoto corresponds to WEBP_PRESET_PHOTO, for outdoor photograph, with natural lighting PresetPhoto Preset = C.WEBP_PRESET_PHOTO // PresetDrawing corresponds to WEBP_PRESET_DRAWING, for hand or line drawing, with high-contrast details PresetDrawing Preset = C.WEBP_PRESET_DRAWING // PresetIcon corresponds to WEBP_PRESET_ICON, for small-sized colorful images PresetIcon Preset = C.WEBP_PRESET_ICON // PresetText corresponds to WEBP_PRESET_TEXT, for text-like PresetText Preset = C.WEBP_PRESET_TEXT )
type YUVAImage ¶
type YUVAImage struct {
Y, Cb, Cr, A []uint8
YStride int
CStride int
AStride int
ColorSpace ColorSpace
Rect image.Rectangle
}
YUVAImage represents a image of YUV colors with alpha channel image.
YUVAImage contains decoded YCbCr image data with alpha channel, but it is not compatible with image.YCbCr. Because, the RGB-YCbCr conversion that used in WebP is following to ITU-R BT.601 standard. In contrast, the conversion of Image.YCbCr (and color.YCbCrModel) is following to the JPEG standard (JFIF). If you need the image as image.YCBCr, you will first convert from WebP to RGB image, then convert from RGB image to JPEG's YCbCr image.
See: http://en.wikipedia.org/wiki/YCbCr
func DecodeYUVA ¶
func DecodeYUVA(data []byte, options *DecoderOptions) (img *YUVAImage, err error)
DecodeYUVA decodes WebP image into YUV image with alpha channel, and returns it as *YUVAImage.
func NewYUVAImage ¶
func NewYUVAImage(r image.Rectangle, c ColorSpace) (image *YUVAImage)
NewYUVAImage creates and allocates image buffer.
Source Files