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Perceptual hashing + locality-sensitive hashing example
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package main | |
import ( | |
"fmt" | |
"image" | |
"image/color" | |
"os" | |
"math" | |
"path/filepath" | |
_ "image/gif" | |
_ "image/png" | |
_ "image/jpeg" | |
"github.com/nfnt/resize" | |
) | |
type IdxHashPair struct { | |
Idx int | |
Hash uint64 | |
} | |
func main() { | |
pattern := "/path/to/images/*" | |
fs, _ := filepath.Glob(pattern) | |
files := make([]string, 0, len(fs)) | |
hashes := make([]uint64, 0, len(fs)) | |
for _, fullPath := range fs { | |
reader, err := os.Open(fullPath) | |
if err != nil { continue } | |
img, _, err := image.Decode(reader) | |
if err != nil { continue } | |
hash := ImagePHash(img) | |
files = append(files, fullPath) | |
hashes = append(hashes, hash) | |
reader.Close() | |
} | |
// create LSH map | |
const Bands = 8 | |
const BandBits = 8 | |
const BandMask = (1 << BandBits) - 1 | |
bands := [Bands][BandMask+1][]IdxHashPair {} | |
for idx, hash := range hashes { | |
for b := 0 ; b < Bands ; b++ { | |
h := hash << uint32(b*BandBits) & BandMask | |
bands[b][h] = append(bands[b][h], IdxHashPair { idx, hash }) | |
} | |
} | |
// compute similarities | |
for idx, hash := range hashes { | |
for b := 0 ; b < Bands ; b++ { | |
h := hash << uint32(b*BandBits) & BandMask | |
for _, candidate := range bands[b][h] { | |
if idx <= candidate.Idx { continue } | |
diff := differentBits(hash, candidate.Hash) | |
if diff < 6 { | |
similarity := 1.0 - (float64(diff) / float64(64)) | |
fmt.Printf("%s %s %d\n", files[idx], files[candidate.Idx], similarity) | |
} | |
} | |
} | |
} | |
} | |
/* based on http://pastebin.com/Pj9d8jt5 */ | |
func ImagePHash(img image.Image) uint64 { | |
c := make([]float64, 32) | |
for i := 1; i < 32; i++ { | |
c[i] = 1 | |
} | |
c[0] = 1 / math.Sqrt(2.0) | |
// Reduce size and reduce color | |
img = grayscale(resize.Resize(32, 32, img, resize.Bilinear)) | |
vals := make([][]float64, 32) | |
for i := range vals { | |
vals[i] = make([]float64, 32) | |
} | |
bounds := img.Bounds() | |
for x := 0; x < bounds.Max.X; x++ { | |
for y := 0; y < bounds.Max.Y; y++ { | |
_, _, b, _ := img.At(x,y).RGBA() | |
vals[x][y] = float64(b) | |
} | |
} | |
/* Compute the DCT */ | |
dctVals := applyDCT(vals, c) | |
// Reduce the DCT and compute the average value (excluding the first term) | |
total := 0.0 | |
for x := 0; x < 8; x++ { | |
for y := 0; y < 8; y++ { | |
total += dctVals[x][y] | |
} | |
} | |
total -= dctVals[0][0] | |
avg := total / float64((8 * 8) - 1) | |
// Further reduce the DCT and create 64 bit hash | |
hash := uint64(0) | |
for x := 0; x < 8; x++ { | |
for y := 0; y < 8; y++ { | |
if !(x == 0 && y == 0) { | |
if dctVals[x][y] > avg { | |
hash = hash | (1 << (63-uint64(x*8+y))) | |
} | |
} | |
} | |
} | |
return hash | |
} | |
// DCT function stolen from http://stackoverflow.com/questions/4240490/problems-with-dct-and-idct-algorithm-in-java | |
func applyDCT(f [][]float64, c []float64) [][]float64 { | |
F := make([][]float64, 32) | |
for i := range F { | |
F[i] = make([]float64, 32) | |
} | |
cosines := [32][32]float64 {} | |
for a := 0; a < 32 ; a++ { | |
for b := 0; b < 32 ; b++ { | |
cosines[a][b] = math.Cos((float64(2*a+1) / float64(2*32)) * float64(b) * math.Pi) | |
} | |
} | |
for u := 0; u < 32; u++ { | |
for v := 0; v < 32; v++ { | |
sum := 0.0 | |
for i := 0; i < 32; i++ { | |
for j := 0; j < 32; j++ { | |
aa := cosines[i][u] | |
bb := cosines[j][v] | |
sum += aa * bb * f[i][j] | |
} | |
} | |
sum *= (c[u]*c[v] / 4.0) | |
F[u][v] = sum | |
} | |
} | |
return F | |
} | |
func grayscale(img image.Image) image.Image { | |
bounds := img.Bounds() | |
gray := image.NewGray(img.Bounds()) | |
for x := bounds.Min.X; x < bounds.Max.X; x++ { | |
for y := bounds.Min.Y; y < bounds.Max.Y; y++ { | |
gray.Set(x, y, color.GrayModel.Convert(img.At(x,y))) | |
} | |
} | |
return gray | |
} | |
func popcount(x uint64) uint64 { | |
x -= (x >> 1) & 0x5555555555555555 | |
x = (x >> 2) & 0x3333333333333333 + x & 0x3333333333333333 | |
x += x >> 4 | |
x &= 0x0f0f0f0f0f0f0f0f | |
x *= 0x0101010101010101 | |
return x >> 56 | |
} | |
func differentBits(a, b uint64) uint64 { | |
return popcount(a ^ b) | |
} |
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