94 lines
2.1 KiB
Go
94 lines
2.1 KiB
Go
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// Copyright 2011 The Graphics-Go 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 detect
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import (
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"image"
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"image/draw"
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)
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// integral is an image.Image-like structure that stores the cumulative
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// sum of the preceding pixels. This allows for O(1) summation of any
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// rectangular region within the image.
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type integral struct {
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// pix holds the cumulative sum of the image's pixels. The pixel at
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// (x, y) starts at pix[(y-rect.Min.Y)*stride + (x-rect.Min.X)*1].
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pix []uint64
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stride int
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rect image.Rectangle
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}
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func (p *integral) at(x, y int) uint64 {
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return p.pix[(y-p.rect.Min.Y)*p.stride+(x-p.rect.Min.X)]
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}
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func (p *integral) sum(b image.Rectangle) uint64 {
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c := p.at(b.Max.X-1, b.Max.Y-1)
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inY := b.Min.Y > p.rect.Min.Y
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inX := b.Min.X > p.rect.Min.X
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if inY && inX {
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c += p.at(b.Min.X-1, b.Min.Y-1)
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}
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if inY {
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c -= p.at(b.Max.X-1, b.Min.Y-1)
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}
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if inX {
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c -= p.at(b.Min.X-1, b.Max.Y-1)
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}
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return c
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}
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func (m *integral) integrate() {
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b := m.rect
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for y := b.Min.Y; y < b.Max.Y; y++ {
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for x := b.Min.X; x < b.Max.X; x++ {
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c := uint64(0)
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if y > b.Min.Y && x > b.Min.X {
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c += m.at(x-1, y)
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c += m.at(x, y-1)
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c -= m.at(x-1, y-1)
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} else if y > b.Min.Y {
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c += m.at(b.Min.X, y-1)
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} else if x > b.Min.X {
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c += m.at(x-1, b.Min.Y)
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}
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m.pix[(y-m.rect.Min.Y)*m.stride+(x-m.rect.Min.X)] += c
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}
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}
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}
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// newIntegrals returns the integral and the squared integral.
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func newIntegrals(src image.Image) (*integral, *integral) {
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b := src.Bounds()
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srcg, ok := src.(*image.Gray)
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if !ok {
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srcg = image.NewGray(b)
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draw.Draw(srcg, b, src, b.Min, draw.Src)
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}
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m := integral{
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pix: make([]uint64, b.Max.Y*b.Max.X),
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stride: b.Max.X,
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rect: b,
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}
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mSq := integral{
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pix: make([]uint64, b.Max.Y*b.Max.X),
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stride: b.Max.X,
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rect: b,
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}
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for y := b.Min.Y; y < b.Max.Y; y++ {
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for x := b.Min.X; x < b.Max.X; x++ {
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os := (y-b.Min.Y)*srcg.Stride + x - b.Min.X
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om := (y-b.Min.Y)*m.stride + x - b.Min.X
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c := uint64(srcg.Pix[os])
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m.pix[om] = c
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mSq.pix[om] = c * c
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}
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}
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m.integrate()
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mSq.integrate()
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return &m, &mSq
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}
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