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pictdiff.go
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pictdiff.go
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// run as standalone binary for best performance (20x difference)
package main
import "image"
import "image/draw"
import _ "image/jpeg"
import "image/png"
import "os"
import "log"
import "fmt"
import "runtime"
func AsList(img *image.RGBA, x int, y int) ([]int) {
off := img.PixOffset(x, y)
r := int(img.Pix[off])
g := int(img.Pix[off + 1])
b := int(img.Pix[off + 2])
a := int(img.Pix[off + 3])
return []int{r, g, b, a}
}
func Abs(x int) (r int) {
r = x
if r < 0 {
r = -r
}
return
}
func Max(x int, y int) (r int) {
r = x
if y > x {
r = y
}
return
}
type calcrowret struct {
Y int
Diff int
Pixels *[]uint8
}
func calcrow(c *chan calcrowret, img1 *image.RGBA, img2 *image.RGBA, y int, width int) {
totaldiff := 0
pixel_list := make([]uint8, width * 4, width * 4)
for x := 0; x < width; x += 1 {
p1 := AsList(img1, x, y)
p2 := AsList(img2, x, y)
totplus := 0
absdiff := Abs(p2[3] - p1[3])
diffpixel := []int{255, 255, 255}
for i := 0; i < 3; i += 1 {
diff := p2[i] - p1[i]
absdiff += Abs(diff)
totplus += Max(0, diff)
diffpixel[i] += diff
}
totaldiff += absdiff
for i := 0; i < 3; i += 1 {
diffpixel[i] -= totplus
if absdiff > 0 && absdiff < 5 {
diffpixel[i] -= 2
}
diffpixel[i] = Max(0, diffpixel[i])
}
pixel_list[x * 4 + 0] = uint8(diffpixel[0])
pixel_list[x * 4 + 1] = uint8(diffpixel[1])
pixel_list[x * 4 + 2] = uint8(diffpixel[2])
pixel_list[x * 4 + 3] = 255
}
*c <- calcrowret{Y: y, Diff: totaldiff, Pixels: &pixel_list}
}
func Load(c *chan *image.RGBA, name string) {
f, err := os.Open(name)
if err != nil {
log.Fatal("Image could not be opened")
}
rimg, _, err := image.Decode(f)
if err != nil {
log.Fatal("Image could not be decoded")
}
width := rimg.Bounds().Dx()
height := rimg.Bounds().Dy()
img := image.NewRGBA(image.Rect(0, 0, width, height))
draw.Draw(img, img.Bounds(), rimg, rimg.Bounds().Min, draw.Src)
*c <- img
}
func main() {
cimg1 := make(chan *image.RGBA)
cimg2 := make(chan *image.RGBA)
if len(os.Args) < 4 {
os.Stderr.WriteString("\n")
os.Stderr.WriteString("Usage: pictdiff <picture A> <picture B> <diff map>\n")
os.Stderr.WriteString("\n")
os.Stderr.WriteString("Example: pictdiff a.png b.png diff.png\n")
os.Stderr.WriteString("\n")
os.Exit(2)
}
go Load(&cimg1, os.Args[1])
go Load(&cimg2, os.Args[2])
img1 := <-cimg1
img2 := <-cimg2
if img1.Bounds() != img2.Bounds() {
log.Fatal("Images don't have the same size")
}
width := img1.Bounds().Dx()
height := img1.Bounds().Dy()
totaldiff := 0
mapimg := image.NewNRGBA(image.Rect(0, 0, width, height))
runtime.GOMAXPROCS(runtime.NumCPU())
diffmeasurements := make(chan calcrowret, height)
for y := 0; y < height; y += 1 {
go calcrow(&diffmeasurements, img1, img2, y, width)
}
for y := 0; y < height; y += 1 {
result := <-diffmeasurements
totaldiff += result.Diff
for x := 0; x < width; x += 1 {
off := mapimg.PixOffset(x, result.Y)
off2 := x * 4
mapimg.Pix[off + 0] = (*result.Pixels)[off2 + 0]
mapimg.Pix[off + 1] = (*result.Pixels)[off2 + 1]
mapimg.Pix[off + 2] = (*result.Pixels)[off2 + 2]
mapimg.Pix[off + 3] = (*result.Pixels)[off2 + 3]
}
}
mapfile, err := os.Create(os.Args[3])
if err != nil {
os.Stderr.WriteString("Cannot open diff map file for writing\n")
} else {
defer mapfile.Close()
err := png.Encode(mapfile, mapimg)
if err != nil {
os.Stderr.WriteString("Cannot write to diff map file\n")
}
}
fmt.Printf("%v\n", totaldiff)
}