forked from remyoudompheng/go-misc
/
main.go
171 lines (159 loc) · 3.5 KB
/
main.go
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package main
import (
"image"
"image/color"
"image/draw"
"image/jpeg"
"log"
"math"
"os"
)
func main() {
input := os.Args[1]
f, err := os.Open(input)
if err != nil {
log.Fatal(err)
}
img, err := jpeg.Decode(f)
f.Close()
if err != nil {
log.Fatal(err)
}
text, bg := split(img)
writeImage(text, input+".text.jpg")
writeImage(bg, input+".bg.jpg")
}
func writeImage(img image.Image, out string) {
f, err := os.Create(out)
if err != nil {
log.Printf("ERROR: %s", err)
return
}
err = jpeg.Encode(f, img, nil)
if err != nil {
log.Printf("ERROR: %s", err)
}
err = f.Close()
if err != nil {
log.Printf("ERROR: %s", err)
}
log.Printf("wrote %s", out)
}
func asYCbCr(c color.Color) color.YCbCr {
return color.YCbCrModel.Convert(c).(color.YCbCr)
}
func split(img image.Image) (textImg, bgImg image.Image) {
size := img.Bounds().Max
text := image.NewGray(img.Bounds())
bg := image.NewRGBA(img.Bounds())
// copy image to background
draw.Src.Draw(bg, img.Bounds(), img, img.Bounds().Min)
// make text white
draw.Src.Draw(text, img.Bounds(), image.NewUniform(color.White), image.Point{})
for x := 0; x+32 <= size.X; x += 16 {
for y := 0; y+32 <= size.Y; y += 16 {
pt := image.Point{X: x, Y: y}
pt2 := image.Point{X: x + 32, Y: y + 32}
col, ok := isBitonal(img, pt)
if ok {
// fill uniform
draw.Src.Draw(bg, image.Rectangle{Min: pt, Max: pt2},
image.NewUniform(col), image.Point{})
// extract text
ref := asYCbCr(col)
for i := 0; i < 32; i++ {
for j := 0; j < 32; j++ {
col := asYCbCr(img.At(x+i, y+j))
val := float64(col.Y) / float64(ref.Y) * 256
if val >= 256 {
val = 255
}
text.SetGray(x+i, y+j, color.Gray{uint8(val)})
}
}
}
}
}
return text, bg
}
var ybuf = image.NewYCbCr(
image.Rectangle{Max: image.Point{32, 32}},
image.YCbCrSubsampleRatio444)
// isBitonal tests whether the image is bitonal and if so,
// returns the background color value
func isBitonal(img image.Image, pt image.Point) (color.Color, bool) {
// convert to YCbCr coordinates
for x := 0; x < 32; x++ {
for y := 0; y < 32; y++ {
value := img.At(pt.X+x, pt.Y+y)
v := asYCbCr(value)
i := 32*y + x
ybuf.Y[i] = v.Y
ybuf.Cb[i] = v.Cb
ybuf.Cr[i] = v.Cr
}
}
// An image is bitonal if:
// - more than 50% of the pixels have constant value (Y0, Cb0, Cr0)
// - other pixels have identical hue, that is,
// (Cb, Cr) = (k * Cb0, k * Cr0)
// find background color
var ystats [256]int
for _, y := range ybuf.Y {
ystats[y]++
}
var z [256]int
z[0] = ystats[0]
var bestY uint8
for i := range z {
if i > 0 {
z[i] = z[i-1] + ystats[i]
}
if i >= 16 {
z[i] -= ystats[i-16]
}
if z[i] > z[bestY] {
bestY = uint8(i)
}
}
if z[bestY] <= len(ybuf.Y)/2 {
return nil, false
}
// compute hue.
var cb, cr float64
for i := range ybuf.Y {
if int(bestY-16) < int(ybuf.Y[i]) && ybuf.Y[i] <= bestY {
cb += float64(ybuf.Cb[i])
cr += float64(ybuf.Cr[i])
}
}
cb /= float64(z[bestY])
cr /= float64(z[bestY])
// test uniformity
for i := range ybuf.Y {
if cb <= 16 {
// handle horizontal/vertical hues
if float64(ybuf.Cb[i]) >= cb+16 {
return nil, false
}
continue
}
if cr <= 16 {
if float64(ybuf.Cr[i]) >= cr+16 {
return nil, false
}
continue
}
b := float64(ybuf.Cb[i]) / cb
r := float64(ybuf.Cr[i]) / cr
if math.Abs(b-r) >= 0.05 {
return nil, false
}
}
if bestY <= 16 {
bestY /= 2
} else {
bestY -= 8
}
return color.YCbCr{Y: bestY, Cb: uint8(cb), Cr: uint8(cr)}, true
}