58 lines
1.1 KiB
Go
58 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 transforms
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import (
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"math"
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)
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// Get result of DCT-II.
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// Follows Matlab dct().
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// Implementation reference:
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// https://unix4lyfe.org/dct-1d/
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func DCT1D(input []float64) []float64 {
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n := len(input)
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out := make([]float64, n)
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for i := 0; i < n; i++ {
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z := 0.0
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for j := 0; j < n; j++ {
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z += input[j] * math.Cos(math.Pi*(float64(j)+0.5)*float64(i)/float64(n))
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}
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if i == 0 {
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z *= math.Sqrt(0.5)
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}
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out[i] = z * math.Sqrt(2.0/float64(n))
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}
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return out
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}
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// Get result of DCT2D by using the seperable property.
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func DCT2D(input [][]float64, w int, h int) [][]float64 {
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output := make([][]float64, h)
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for i := range output {
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output[i] = make([]float64, w)
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}
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for i := 0; i < h; i++ {
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cols := DCT1D(input[i])
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copy(output[i], cols)
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}
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for i := 0; i < w; i++ {
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in := make([]float64, h)
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for j := 0; j < h; j++ {
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in[j] = output[j][i]
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}
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rows := DCT1D(in)
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for j := 0; j < len(rows); j++ {
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output[j][i] = rows[j]
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}
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}
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return output
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}
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