//BackProjectGray computes back projection of img
// in Gray16 by performing an addition
// of backprojection by line.
// 16Gray avoids white noise.
func BackProjectGray(img image.Gray) (*image.Gray16, error) {
size := img.Bounds().Size()
width := size.Y
nbProj := size.X
step := 180.0 / float64(nbProj)
out := image.NewGray16(image.Rect(0, 0, width, width))
for X := 0; X < nbProj; X++ {
//Extract a 1D-projection (one row Y of sinogram)
line := img.SubImage(image.Rect(X, 0, X+1, width)).(*image.Gray)
// 3- Do the backprojection and rotate accordingly
wideLine := resize.Resize(uint(width), uint(width), line, resize.Lanczos3).(*image.Gray)
θ := manipulator.Rad(float64(X)*step) + math.Pi/2
rotatedWideLine := image.NewGray(image.Rect(0, 0, width, width))
err := graphics.Rotate(rotatedWideLine, wideLine, &graphics.RotateOptions{Angle: θ})
if err != nil {
return out, err
}
// 4- Add the rotated backprojection in the output image
for x := 0; x < width; x++ {
for y := 0; y < width; y++ {
point := uint16(out.At(x, y).(color.Gray16).Y) + uint16(rotatedWideLine.At(x, y).(color.Gray).Y)
out.Set(x, y, color.Gray16{uint16(point)})
}
}
}
return out, nil
}
//ProjectGray returns a greyscale sinogram (or radon projection) of img
// N(default: 360): number of image rotation on which a projection will be done
// A naive simplistic approach
// Sinograms looks like this :
// θ1 θ2 θ3...θN
// | | | |
// | | | |
func ProjectGray(src image.Image, N int) (*image.Gray, error) {
if N == 0 {
N = 360
}
step := 180.0 / float64(N)
size := src.Bounds().Size()
overX := int(float64(size.X) * 1.1)
overY := int(float64(size.Y) * 1.1)
var img image.Image = image.NewGray(image.Rect(0, 0, size.X+overX, size.Y+overY))
img = imaging.Overlay(img, src, image.Pt(overX/2, overY/2), 1)
size = img.Bounds().Size()
D := max(size.X, size.Y)
out := image.NewGray(image.Rect(0, 0, N, D))
// for each given angle θ
for n := 0; n < N; n++ {
θ := float64(n) * step
draw := image.NewRGBA(image.Rect(0, 0, img.Bounds().Dy(), img.Bounds().Dx()))
//have a duplicate img rotated by θ
err := graphics.Rotate(draw, img, &graphics.RotateOptions{Angle: manipulator.Rad(θ)})
if err != nil {
return out, err
}
sinogram := make([]float64, size.X)
// get column average profile
for y := 0; y < size.Y; y++ {
for x := 0; x < size.X; x++ {
greyColor, _ := color.GrayModel.Convert(draw.At(x, y)).(color.Gray)
sinogram[x] = sinogram[x] + float64(greyColor.Y)
}
}
//Set out line with sinogram
for d := 0; d < D; d++ {
out.Set(n, d, color.Gray{uint8(sinogram[d] / float64(size.Y))})
}
}
return out, nil
}
