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package preproc
// TODO: add minimum size variable (default ~30%?)
// TODO: have the integral image specific stuff done by interface functions
import (
"image"
"image/color"
)
type windowslice struct {
topleft uint64
topright uint64
bottomleft uint64
bottomright uint64
}
func getwindowslice(i [][]uint64, x int, size int) windowslice {
maxy := len(i) - 1
maxx := x + size
if maxx > len(i[0])-1 {
maxx = len(i[0]) - 1
}
return windowslice{i[0][x], i[0][maxx], i[maxy][x], i[maxy][maxx]}
}
// checkwindow checks the window from x to see whether more than
// thresh proportion of the pixels are white, if so it returns true.
func checkwindow(integral [][]uint64, x int, size int, thresh float64) bool {
height := len(integral)
window := getwindowslice(integral, x, size)
// divide by 255 as each on pixel has the value of 255
sum := (window.bottomright + window.topleft - window.topright - window.bottomleft) / 255
area := size * height
proportion := float64(area)/float64(sum) - 1
return proportion <= thresh
}
// returns the proportion of the given window that is black pixels
func proportion(integral [][]uint64, x int, size int) float64 {
height := len(integral)
window := getwindowslice(integral, x, size)
// divide by 255 as each on pixel has the value of 255
sum := (window.bottomright + window.topleft - window.topright - window.bottomleft) / 255
area := size * height
return float64(area)/float64(sum) - 1
}
// findbestedge goes through every vertical line from x to x+w to
// find the one with the lowest proportion of black pixels.
func findbestedge(integral [][]uint64, x int, w int) int {
var bestx int
var best float64
if w == 1 {
return x
}
right := x + w
for ; x < right; x++ {
prop := proportion(integral, x, 1)
if prop > best {
best = prop
bestx = x
}
}
return bestx
}
// Findedges finds the edges of the main content, by moving a window of wsize
// from the middle of the image to the left and right, stopping when it reaches
// a point at which there is a lower proportion of black pixels than thresh.
func Findedges(integral [][]uint64, wsize int, thresh float64) (int, int) {
maxx := len(integral[0]) - 1
var lowedge, highedge int = 0, maxx
for x := maxx / 2; x < maxx-wsize; x++ {
if checkwindow(integral, x, wsize, thresh) {
highedge = findbestedge(integral, x, wsize)
break
}
}
for x := maxx / 2; x > 0; x-- {
if checkwindow(integral, x, wsize, thresh) {
lowedge = findbestedge(integral, x, wsize)
break
}
}
return lowedge, highedge
}
// Wipesides fills the sections of image not within the boundaries
// of lowedge and highedge with white
func Wipesides(img *image.Gray, lowedge int, highedge int) *image.Gray {
b := img.Bounds()
new := image.NewGray(b)
// set left edge white
for x := b.Min.X; x < lowedge; x++ {
for y := b.Min.Y; y < b.Max.Y; y++ {
new.SetGray(x, y, color.Gray{255})
}
}
// copy middle
for x := lowedge; x < highedge; x++ {
for y := b.Min.Y; y < b.Max.Y; y++ {
new.SetGray(x, y, img.GrayAt(x, y))
}
}
// set right edge white
for x := highedge; x < b.Max.X; x++ {
for y := b.Min.Y; y < b.Max.Y; y++ {
new.SetGray(x, y, color.Gray{255})
}
}
return new
}
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