59 lines
1.2 KiB
Go
59 lines
1.2 KiB
Go
// Copyright 2017 The goimagehash Authors. All rights reserved.
|
|
// Use of this source code is governed by a BSD-style
|
|
// license that can be found in the LICENSE file.
|
|
|
|
package etcs
|
|
|
|
// MeanOfPixels function returns a mean of pixels.
|
|
func MeanOfPixels(pixels []float64) float64 {
|
|
m := 0.0
|
|
lens := len(pixels)
|
|
if lens == 0 {
|
|
return 0
|
|
}
|
|
|
|
for _, p := range pixels {
|
|
m += p
|
|
}
|
|
|
|
return m / float64(lens)
|
|
}
|
|
|
|
// MedianOfPixels function returns a median value of pixels.
|
|
// It uses quick selection algorithm.
|
|
func MedianOfPixels(pixels []float64) float64 {
|
|
tmp := make([]float64, len(pixels))
|
|
copy(tmp, pixels)
|
|
l := len(tmp) - 1
|
|
pos := l / 2
|
|
v := quickSelect(tmp, 0, l, pos)
|
|
return v
|
|
}
|
|
|
|
func quickSelect(sequence []float64, low int, hi int, k int) float64 {
|
|
if hi-low <= 1 {
|
|
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)
|
|
}
|
|
|
|
if k > j {
|
|
return quickSelect(sequence, j+1, hi, k-j)
|
|
}
|
|
|
|
return sequence[j]
|
|
}
|