110 lines
2.8 KiB
Go
110 lines
2.8 KiB
Go
package blurhash
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import (
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"fmt"
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"github.com/buckket/go-blurhash/base83"
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"image"
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"image/color"
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"math"
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)
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// An InvalidHashError occurs when the given hash is either too short or the length does not match its size flag.
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type InvalidHashError string
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func (e InvalidHashError) Error() string {
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return fmt.Sprintf("blurhash: %s", string(e))
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}
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// Components decodes and returns the number of x and y components in the given BlurHash.
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func Components(hash string) (xComponents, yComponents int, err error) {
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if len(hash) < 6 {
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return 0, 0, InvalidHashError("hash is invalid (too short)")
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}
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sizeFlag, err := base83.Decode(string(hash[0]))
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if err != nil {
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return 0, 0, err
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}
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yComponents = (sizeFlag / 9) + 1
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xComponents = (sizeFlag % 9) + 1
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if len(hash) != 4+2*xComponents*yComponents {
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return 0, 0, InvalidHashError("hash is invalid (length mismatch)")
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}
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return xComponents, yComponents, nil
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}
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// Decode generates an image of the given BlurHash with a size of width and height.
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// Punch is a multiplier that adjusts the contrast of the resulting image.
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func Decode(hash string, width, height, punch int) (image.Image, error) {
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xComp, yComp, err := Components(hash)
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if err != nil {
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return nil, err
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}
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quantisedMaximumValue, err := base83.Decode(string(hash[1]))
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if err != nil {
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return nil, err
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}
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maximumValue := (float64(quantisedMaximumValue) + 1) / 166
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if punch == 0 {
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punch = 1
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}
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colors := make([][3]float64, xComp*yComp)
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for i := range colors {
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if i == 0 {
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value, err := base83.Decode(hash[2:6])
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if err != nil {
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return nil, err
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}
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colors[i] = decodeDC(value)
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} else {
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value, err := base83.Decode(hash[4+i*2 : 6+i*2])
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if err != nil {
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return nil, err
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}
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colors[i] = decodeAC(value, maximumValue*float64(punch))
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}
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}
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img := image.NewNRGBA(image.Rect(0, 0, width, height))
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for y := 0; y < height; y++ {
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for x := 0; x < width; x++ {
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var r, g, b float64
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for j := 0; j < yComp; j++ {
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for i := 0; i < xComp; i++ {
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basis := math.Cos(math.Pi*float64(x)*float64(i)/float64(width)) *
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math.Cos(math.Pi*float64(y)*float64(j)/float64(height))
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pcolor := colors[i+j*xComp]
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r += pcolor[0] * basis
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g += pcolor[1] * basis
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b += pcolor[2] * basis
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}
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}
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img.SetNRGBA(x, y, color.NRGBA{R: uint8(linearTosRGB(r)), G: uint8(linearTosRGB(g)), B: uint8(linearTosRGB(b)), A: 255})
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}
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}
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return img, nil
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}
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func decodeDC(value int) [3]float64 {
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return [3]float64{sRGBToLinear(value >> 16), sRGBToLinear(value >> 8 & 255), sRGBToLinear(value & 255)}
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}
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func decodeAC(value int, maximumValue float64) [3]float64 {
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quantR := math.Floor(float64(value) / (19 * 19))
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quantG := math.Mod(math.Floor(float64(value)/19), 19)
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quantB := math.Mod(float64(value), 19)
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sp := func(quant float64) float64 {
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return signPow((quant-9)/9, 2.0) * maximumValue
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}
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return [3]float64{sp(quantR), sp(quantG), sp(quantB)}
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}
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