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-rw-r--r--preproc/wipesides.go122
1 files changed, 122 insertions, 0 deletions
diff --git a/preproc/wipesides.go b/preproc/wipesides.go
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+++ b/preproc/wipesides.go
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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
+}