Update to v0.2.1 of integralimg, and improve various things

- Improve integral sauvola by rounding threshold correctly
- The Sauvola functions can now process any image.Image, not
  just an image.Gray
- Add ImageWindower interface and use it to generalise
  wipesides.go
- Rely on Bounds() for image bounds rather than implementation-
  specific stuff in integralimg

Note that a couple of the wipesides tests are now failing. It's
possible that this is due to fixed or introduced bugs (let's hope
the former) changing sensible thresholds. Will need to look into
this and sort it.

1 files changed, 15 insertions, 12 deletions

diff --git a/wipesides.go b/wipesides.go
index 26b7d25..e87d209 100644
--- a/wipesides.go
+++ b/wipesides.go
@@ -4,7 +4,6 @@
 
 package preproc
 
-// TODO: switch to an interface rather than integralimg.I
 // TODO: optionally return the edges chosen
 
 import (
@@ -21,7 +20,7 @@ import (
 )
 
 // returns the proportion of the given window that is black pixels
-func proportion(i integralimg.I, x int, size int) float64 {
+func proportion(i ImageWindower, x int, size int) float64 {
 	w := i.GetVerticalWindow(x, size)
 	return w.Proportion()
 }
@@ -30,7 +29,7 @@ func proportion(i integralimg.I, x int, size int) float64 {
 // find the one with the lowest proportion of black pixels.
 // if there are multiple lines with the same proportion (e.g. zero),
 // choose the middle one.
-func findbestedge(img integralimg.I, x int, w int) int {
+func findbestedge(img ImageWindower, x int, w int) int {
 	var best float64
 	var bestxs []int
 
@@ -59,8 +58,8 @@ func findbestedge(img integralimg.I, x int, w int) int {
 // 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
+func findedges(img ImageWindower, wsize int, thresh float64) (int, int) {
+	maxx := img.Bounds().Dx() - 1
 	var lowedge, highedge int = 0, maxx
 
 	// don't start at the middle, as this will fail for 2 column layouts,
@@ -88,8 +87,8 @@ func findedges(img integralimg.I, wsize int, thresh float64) (int, int) {
 // but working from the outside of the image inwards, rather than from the
 // middle outwards.
 // TODO: test what difference this makes
-func findedgesOutin(img integralimg.I, wsize int, thresh float64) (int, int) {
-	maxx := len(img[0]) - 1
+func findedgesOutin(img ImageWindower, wsize int, thresh float64) (int, int) {
+	maxx := img.Bounds().Dx() - 1
 	var lowedge, highedge int = 0, maxx
 
 	for x := maxx-wsize; x > 0; x-- {
@@ -165,8 +164,10 @@ func sideways(img *image.Gray) *image.Gray {
 // 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)
+	b := img.Bounds()
+	intImg := integralimg.NewImage(b)
+	draw.Draw(intImg, b, img, b.Min, draw.Src)
+	lowedge, highedge := findedges(*intImg, wsize, thresh)
 	if toonarrow(img, lowedge, highedge, min) {
 		return img
 	}
@@ -177,9 +178,11 @@ func Wipe(img *image.Gray, wsize int, thresh float64, min int) *image.Gray {
 // content area with white, providing the content area is above min %
 func VWipe(img *image.Gray, wsize int, thresh float64, min int) *image.Gray {
 	rotimg := sideways(img)
-	integral := integralimg.ToIntegralImg(rotimg)
+	b := rotimg.Bounds()
+	intImg := integralimg.NewImage(b)
+	draw.Draw(intImg, b, rotimg, b.Min, draw.Src)
 	// TODO: test whether there are any places where Outin makes a real difference
-	lowedge, highedge:= findedgesOutin(integral, wsize, thresh)
+	lowedge, highedge:= findedgesOutin(*intImg, wsize, thresh)
 	if toonarrow(img, lowedge, highedge, min) {
 		return img
 	}
@@ -200,10 +203,10 @@ func VWipe(img *image.Gray, wsize int, thresh float64, min int) *image.Gray {
 // vmin: minimum % of content area height to consider valid.
 func WipeFile(inPath string, outPath string, hwsize int, hthresh float64, hmin int, vwsize int, vthresh float64, vmin 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))
 	}
+	defer f.Close()
 	img, _, err := image.Decode(f)
 	if err != nil {
 		return errors.New(fmt.Sprintf("Could not decode image: %v", err))