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