package preproc // TODO: add minimum size variable (default ~30%?) // TODO: have the integral image specific stuff done by interface functions import ( "image" "image/color" "rescribe.xyz/go.git/binarize" ) 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 } // wipe fills the sections of image which fall outside the content // area with white func Wipe(img *image.Gray, wsize int, thresh float64) *image.Gray { integral := binarize.Integralimg(img) lowedge, highedge := findedges(integral, wsize, thresh) return wipesides(img, lowedge, highedge) }