Documentation
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Overview ¶
Package sharpyuv implements sharp RGB to YUV420 conversion that minimizes chroma subsampling artifacts using iterative error diffusion.
This is a pure Go port of libwebp's sharpyuv library.
Index ¶
- Variables
- func Convert(rgb []byte, width, height, rgbStride int, yuv *image.YCbCr, opts *Options) error
- func GammaToLinear(v uint16, bitDepth int, tf TransferFunc) uint32
- func LinearToGamma(v uint32, bitDepth int, tf TransferFunc) uint16
- type ColorSpace
- type ConversionMatrix
- type MatrixType
- type Options
- type Range
- type TransferFunc
Constants ¶
This section is empty.
Variables ¶
var ( BT601 = ColorSpace{Kr: 0.2990, Kb: 0.1140, BitDepth: 8, Range: RangeLimited} BT709 = ColorSpace{Kr: 0.2126, Kb: 0.0722, BitDepth: 8, Range: RangeLimited} BT601Full = ColorSpace{Kr: 0.2990, Kb: 0.1140, BitDepth: 8, Range: RangeFull} BT709Full = ColorSpace{Kr: 0.2126, Kb: 0.0722, BitDepth: 8, Range: RangeFull} )
Predefined color spaces.
Functions ¶
func Convert ¶
Convert performs RGB to YUV420 conversion. When opts.SharpEnabled is true, it uses the sharp iterative algorithm that minimizes chroma subsampling artifacts. Otherwise it uses simple averaging.
rgb must be packed RGB (3 bytes per pixel, row-major). The result is written to the provided YCbCr image which must be allocated with 4:2:0 subsampling and matching dimensions.
func GammaToLinear ¶
func GammaToLinear(v uint16, bitDepth int, tf TransferFunc) uint32
GammaToLinear converts a gamma-encoded value (in the range of bitDepth bits) to a 16-bit linear value using the specified transfer function.
func LinearToGamma ¶
func LinearToGamma(v uint32, bitDepth int, tf TransferFunc) uint16
LinearToGamma converts a 16-bit linear value to a gamma-encoded value in the range of bitDepth bits using the specified transfer function.
Types ¶
type ColorSpace ¶
type ColorSpace struct {
Kr float64 // Luma coefficient for red
Kb float64 // Luma coefficient for blue
BitDepth int // 8, 10, or 12
Range Range
}
ColorSpace defines the color primaries for YUV conversion.
type ConversionMatrix ¶
ConversionMatrix holds the RGB to YUV conversion coefficients in 16-bit fixed point.
The conversion is:
y = (RGBToY[0]*r + RGBToY[1]*g + RGBToY[2]*b + RGBToY[3] + (1<<15)) >> 16 u = (RGBToU[0]*r + RGBToU[1]*g + RGBToU[2]*b + RGBToU[3] + (1<<15)) >> 16 v = (RGBToV[0]*r + RGBToV[1]*g + RGBToV[2]*b + RGBToV[3] + (1<<15)) >> 16
func ComputeConversionMatrix ¶
func ComputeConversionMatrix(cs *ColorSpace) *ConversionMatrix
ComputeConversionMatrix fills a ConversionMatrix from a ColorSpace definition.
func GetConversionMatrix ¶
func GetConversionMatrix(mt MatrixType) *ConversionMatrix
GetConversionMatrix returns a predefined conversion matrix.
type MatrixType ¶
type MatrixType int
MatrixType identifies a predefined conversion matrix.
const ( MatrixWebP MatrixType = iota MatrixRec601Limited MatrixRec601Full MatrixRec709Limited MatrixRec709Full )
type Options ¶
type Options struct {
Matrix *ConversionMatrix
TransferType TransferFunc
SharpEnabled bool // When false, use standard (averaging) downsampling
}
Options controls the SharpYUV conversion.
func DefaultOptions ¶
func DefaultOptions() *Options
DefaultOptions returns default options using the WebP matrix and sRGB transfer.
type TransferFunc ¶
type TransferFunc int
TransferFunc identifies a transfer function (OETF/EOTF) as defined in H.273.
const ( TransferBT709 TransferFunc = 1 TransferBT470M TransferFunc = 4 TransferBT470BG TransferFunc = 5 TransferBT601 TransferFunc = 6 TransferSMPTE240 TransferFunc = 7 TransferLinear TransferFunc = 8 TransferLog100 TransferFunc = 9 TransferLog100Sqrt TransferFunc = 10 TransferIEC61966 TransferFunc = 11 TransferBT1361 TransferFunc = 12 TransferSRGB TransferFunc = 13 TransferBT2020_10 TransferFunc = 14 TransferBT2020_12 TransferFunc = 15 TransferPQ TransferFunc = 16 // SMPTE 2084 TransferSMPTE428 TransferFunc = 17 TransferHLG TransferFunc = 18 )
Source Files