lordwelch/goimagehash
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goimagehash: Fix quickselect algorithm to pick median value.

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This commit is contained in:
Dong-hee Na 2018-05-08 12:54:48 +09:00
parent ad2b6ded3b
commit 1903317145
3 changed files with 31 additions and 28 deletions
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45
etcs/utils.go
View File

@ -24,35 +24,38 @@ func MeanOfPixels(pixels []float64) float64 {
func MedianOfPixels(pixels []float64) float64 {
tmp := make([]float64, len(pixels))
copy(tmp, pixels)
l := len(tmp) - 1
l := len(tmp)
pos := l / 2
v := quickSelect(tmp, 0, l, pos)
v := quickSelectMedian(tmp, 0, l-1, pos)
return v
}
func quickSelect(sequence []float64, low int, hi int, k int) float64 {
if hi-low <= 1 {
func quickSelectMedian(sequence []float64, low int, hi int, k int) float64 {
if low == hi {
return sequence[k]
}
j := low
sequence[j], sequence[k] = sequence[k], sequence[j]
j++
for i := j; i < hi; i++ {
if sequence[i] < sequence[low] {
sequence[j], sequence[i] = sequence[i], sequence[j]
j++
}
}
j--
sequence[j], sequence[low] = sequence[low], sequence[j]
if k < j {
return quickSelect(sequence, low, j, k)
for low < hi {
pivot := low/2 + hi/2
pivotValue := sequence[pivot]
storeIdx := low
sequence[pivot], sequence[hi] = sequence[hi], sequence[pivot]
for i := low; i < hi; i++ {
if sequence[i] < pivotValue {
sequence[storeIdx], sequence[i] = sequence[i], sequence[storeIdx]
storeIdx++
}
}
sequence[hi], sequence[storeIdx] = sequence[storeIdx], sequence[hi]
if k <= storeIdx {
hi = storeIdx
} else {
low = storeIdx + 1
}
}
if k > j {
return quickSelect(sequence, j+1, hi, k-j)
if len(sequence)%2 == 0 {
return sequence[k-1]/2 + sequence[k]/2
}
return sequence[j]
return sequence[k]
}

4
etcs/utils_test.go
View File

@ -30,9 +30,9 @@ func TestMedianPixels(t *testing.T) {
}{
{[]float64{0, 0, 0, 0}, 0},
{[]float64{1}, 1},
{[]float64{1, 2, 3, 4}, 2},
{[]float64{1, 2, 3, 4}, 2.5},
{[]float64{5, 3, 1, 7, 9}, 5},
{[]float64{98.3, 33.4, 105.44, 1500.4, 22.5, 66.6}, 98.3},
{[]float64{98.3, 33.4, 105.44, 1500.4, 22.5, 66.6}, 82.44999999999999},
} {
pixels := tt.pixels
result := MedianOfPixels(pixels)

10
hashcompute_test.go
View File

@ -41,11 +41,11 @@ func TestHashCompute(t *testing.T) {
{"_examples/sample2.jpg", "_examples/sample2.jpg", PerceptionHash, "PerceptionHash", 0},
{"_examples/sample3.jpg", "_examples/sample3.jpg", PerceptionHash, "PerceptionHash", 0},
{"_examples/sample4.jpg", "_examples/sample4.jpg", PerceptionHash, "PerceptionHash", 0},
{"_examples/sample1.jpg", "_examples/sample2.jpg", PerceptionHash, "PerceptionHash", 34},
{"_examples/sample1.jpg", "_examples/sample3.jpg", PerceptionHash, "PerceptionHash", 7},
{"_examples/sample1.jpg", "_examples/sample4.jpg", PerceptionHash, "PerceptionHash", 31},
{"_examples/sample2.jpg", "_examples/sample3.jpg", PerceptionHash, "PerceptionHash", 31},
{"_examples/sample2.jpg", "_examples/sample4.jpg", PerceptionHash, "PerceptionHash", 23},
{"_examples/sample1.jpg", "_examples/sample2.jpg", PerceptionHash, "PerceptionHash", 32},
{"_examples/sample1.jpg", "_examples/sample3.jpg", PerceptionHash, "PerceptionHash", 2},
{"_examples/sample1.jpg", "_examples/sample4.jpg", PerceptionHash, "PerceptionHash", 30},
{"_examples/sample2.jpg", "_examples/sample3.jpg", PerceptionHash, "PerceptionHash", 34},
{"_examples/sample2.jpg", "_examples/sample4.jpg", PerceptionHash, "PerceptionHash", 20},
} {
file1, err := os.Open(tt.img1)
if err != nil {