gtsocial-umbx

encode.go (4799B)

---

 package blurhash
 
 import (
 	"fmt"
 	"github.com/buckket/go-blurhash/base83"
 	"image"
 	"math"
 	"strings"
 )
 
 func init() {
 	initLinearTable(channelToLinear[:])
 }
 
 var channelToLinear [256]float64
 
 func initLinearTable(table []float64) {
 	for i := range table {
 		channelToLinear[i] = sRGBToLinear(i)
 	}
 }
 
 // An InvalidParameterError occurs when an invalid argument is passed to either the Decode or Encode function.
 type InvalidParameterError struct {
 	Value     int
 	Parameter string
 }
 
 func (e InvalidParameterError) Error() string {
 	return fmt.Sprintf("blurhash: %sComponents (%d) must be element of [1-9]", e.Parameter, e.Value)
 }
 
 // An EncodingError represents an error that occurred during the encoding of the given value.
 // This most likely means that your input image is invalid and can not be processed.
 type EncodingError string
 
 func (e EncodingError) Error() string {
 	return fmt.Sprintf("blurhash: %s", string(e))
 }
 
 // Encode calculates the Blurhash for an image using the given x and y component counts.
 // The x and y components have to be between 1 and 9 respectively.
 // The image must be of image.Image type.
 func Encode(xComponents int, yComponents int, rgba image.Image) (string, error) {
 	if xComponents < 1 || xComponents > 9 {
 		return "", InvalidParameterError{xComponents, "x"}
 	}
 	if yComponents < 1 || yComponents > 9 {
 		return "", InvalidParameterError{yComponents, "y"}
 	}
 
 	var blurhash strings.Builder
 	blurhash.Grow(4 + 2*xComponents*yComponents)
 
 	// Size Flag
 	str, err := base83.Encode((xComponents-1)+(yComponents-1)*9, 1)
 	if err != nil {
 		return "", EncodingError("could not encode size flag")
 	}
 	blurhash.WriteString(str)
 
 	factors := make([]float64, yComponents*xComponents*3)
 	multiplyBasisFunction(rgba, factors, xComponents, yComponents)
 
 	var maximumValue float64
 	var quantisedMaximumValue int
 	var acCount = xComponents*yComponents - 1
 	if acCount > 0 {
 		var actualMaximumValue float64
 		for i := 0; i < acCount*3; i++ {
 			actualMaximumValue = math.Max(math.Abs(factors[i+3]), actualMaximumValue)
 		}
 		quantisedMaximumValue = int(math.Max(0, math.Min(82, math.Floor(actualMaximumValue*166-0.5))))
 		maximumValue = (float64(quantisedMaximumValue) + 1) / 166
 	} else {
 		maximumValue = 1
 	}
 
 	// Quantised max AC component
 	str, err = base83.Encode(quantisedMaximumValue, 1)
 	if err != nil {
 		return "", EncodingError("could not encode quantised max AC component")
 	}
 	blurhash.WriteString(str)
 
 	// DC value
 	str, err = base83.Encode(encodeDC(factors[0], factors[1], factors[2]), 4)
 	if err != nil {
 		return "", EncodingError("could not encode DC value")
 	}
 	blurhash.WriteString(str)
 
 	// AC values
 	for i := 0; i < acCount; i++ {
 		str, err = base83.Encode(encodeAC(factors[3+(i*3+0)], factors[3+(i*3+1)], factors[3+(i*3+2)], maximumValue), 2)
 		if err != nil {
 			return "", EncodingError("could not encode AC value")
 		}
 		blurhash.WriteString(str)
 	}
 
 	if blurhash.Len() != 4+2*xComponents*yComponents {
 		return "", EncodingError("hash does not match expected size")
 	}
 
 	return blurhash.String(), nil
 }
 
 func multiplyBasisFunction(rgba image.Image, factors []float64, xComponents int, yComponents int) {
 	height := rgba.Bounds().Max.Y
 	width := rgba.Bounds().Max.X
 
 	xvalues := make([][]float64, xComponents)
 	for xComponent := 0; xComponent < xComponents; xComponent++ {
 		xvalues[xComponent] = make([]float64, width)
 		for x := 0; x < width; x++ {
 			xvalues[xComponent][x] = math.Cos(math.Pi * float64(xComponent) * float64(x) / float64(width))
 		}
 	}
 
 	yvalues := make([][]float64, yComponents)
 	for yComponent := 0; yComponent < yComponents; yComponent++ {
 		yvalues[yComponent] = make([]float64, height)
 		for y := 0; y < height; y++ {
 			yvalues[yComponent][y] = math.Cos(math.Pi * float64(yComponent) * float64(y) / float64(height))
 		}
 	}
 
 	for y := 0; y < height; y++ {
 		for x := 0; x < width; x++ {
 			rt, gt, bt, _ := rgba.At(x, y).RGBA()
 			lr := channelToLinear[rt>>8]
 			lg := channelToLinear[gt>>8]
 			lb := channelToLinear[bt>>8]
 
 			for yc := 0; yc < yComponents; yc++ {
 				for xc := 0; xc < xComponents; xc++ {
 
 					scale := 1 / float64(width*height)
 
 					if xc != 0 || yc != 0 {
 						scale = 2 / float64(width*height)
 					}
 
 					basis := xvalues[xc][x] * yvalues[yc][y]
 					factors[0+xc*3+yc*3*xComponents] += lr * basis * scale
 					factors[1+xc*3+yc*3*xComponents] += lg * basis * scale
 					factors[2+xc*3+yc*3*xComponents] += lb * basis * scale
 				}
 			}
 		}
 	}
 }
 
 func encodeDC(r, g, b float64) int {
 	return (linearTosRGB(r) << 16) + (linearTosRGB(g) << 8) + linearTosRGB(b)
 }
 
 func encodeAC(r, g, b, maximumValue float64) int {
 	quant := func(f float64) int {
 		return int(math.Max(0, math.Min(18, math.Floor(signPow(f/maximumValue, 0.5)*9+9.5))))
 	}
 	return quant(r)*19*19 + quant(g)*19 + quant(b)
 }