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// Copyright 2019 Nick White.
// Use of this source code is governed by the GPLv3
// license that can be found in the LICENSE file.
package preproc
// TODO: add minimum size variable (default ~30%?)
// TODO: switch to an interface rather than integralimg.I
import (
"errors"
"fmt"
"image"
"image/color"
"image/draw"
_ "image/jpeg"
"image/png"
"os"
"rescribe.xyz/preproc/integralimg"
)
// returns the proportion of the given window that is black pixels
func proportion(i integralimg.I, x int, size int) float64 {
w := i.GetVerticalWindow(x, size)
return w.Proportion()
}
// findbestedge goes through every vertical line from x to x+w to
// find the one with the lowest proportion of black pixels.
func findbestedge(img integralimg.I, 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(img, 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 near 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(img integralimg.I, wsize int, thresh float64) (int, int) {
maxx := len(img[0]) - 1
var lowedge, highedge int = 0, maxx
// don't start at the middle, as this will fail for 2 column layouts,
// start 10% left or right of the middle
notcentre := maxx / 10
for x := maxx/2 + notcentre; x < maxx-wsize; x++ {
if proportion(img, x, wsize) <= thresh {
highedge = findbestedge(img, x, wsize)
break
}
}
for x := maxx/2 - notcentre; x > 0; x-- {
if proportion(img, x, wsize) <= thresh {
lowedge = findbestedge(img, 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
}
// toonarrow checks whether the area between lowedge and highedge is
// less than min % of the total image width
func toonarrow(img *image.Gray, lowedge int, highedge int, min int) bool {
b := img.Bounds()
imgw := b.Max.X - b.Min.X
wipew := highedge - lowedge
if float64(wipew)/float64(imgw)*100 < float64(min) {
return true
}
return false
}
// Wipe fills the sections of image which fall outside the content
// area with white, providing the content area is above min %
func Wipe(img *image.Gray, wsize int, thresh float64, min int) *image.Gray {
integral := integralimg.ToIntegralImg(img)
lowedge, highedge := findedges(integral, wsize, thresh)
if toonarrow(img, lowedge, highedge, min) {
return img
}
return wipesides(img, lowedge, highedge)
}
// WipeFile wipes an image file, filling the sections of the image
// which fall outside the content area with white, providing the
// content area is above min %.
// inPath: path of the input image.
// outPath: path to save the output image.
// wsize: window size for wipe algorithm.
// thresh: threshold for wipe algorithm.
// min: minimum % of content area width to consider valid.
func WipeFile(inPath string, outPath string, wsize int, thresh float64, min int) error {
f, err := os.Open(inPath)
defer f.Close()
if err != nil {
return errors.New(fmt.Sprintf("Could not open file %s: %v", inPath, err))
}
img, _, err := image.Decode(f)
if err != nil {
return errors.New(fmt.Sprintf("Could not decode image: %v", err))
}
b := img.Bounds()
gray := image.NewGray(image.Rect(0, 0, b.Dx(), b.Dy()))
draw.Draw(gray, b, img, b.Min, draw.Src)
clean := Wipe(gray, wsize, thresh, min)
f, err = os.Create(outPath)
if err != nil {
return errors.New(fmt.Sprintf("Could not create file %s: %v", outPath, err))
}
defer f.Close()
err = png.Encode(f, clean)
if err != nil {
return errors.New(fmt.Sprintf("Could not encode image: %v", err))
}
return nil
}
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