func PlotSpectogram(sr Reader, outpath string, from, to int) error {
d, err := dft(sr, from, to)
if err != nil {
return err
}
// make image
height, width := len(d[0]), len(d)
image := image.NewGray(image.Rect(0, 0, width, height))
// find maximum value in DFT
max := maxAmp(d)
max = math.Log(1 + max)
// plot each point on image
for i, col := range d {
for j, amp := range col {
// Log(Xk+1) will give us a positive value
// Using log here allows low amplitudes to be more visible
bright := uint8(float64(255) * math.Log(1+amp) / max)
image.Set(i, height-j, color.RGBA{bright, bright, bright, 255})
}
}
of, err := os.Create(outpath)
if err != nil {
return err
}
return png.Encode(of, image)
}
func PlotOscillogram(sr Reader, outpath string, from, to int) error {
// make image
height, width := 255, to-from
gray := color.RGBA{255, 0, 0, 255}
image := image.NewGray(image.Rect(0, 0, width, height*2))
// plot each point on image + a central gray line at 0
var amp float64
for t := from; t < to; t++ {
amp = float64(height) * (sr.Get(0, t) * 2)
image.Set(t, int(amp), color.White)
image.Set(t, height, gray)
}
of, err := os.Create(outpath)
if err != nil {
return err
}
return png.Encode(of, image)
}
func matrixToImage(mx *[][]int, width, height int, log bool) *image.RGBA {
if log {
if !equalize_log(mx, 255, .995, .0005) {
return nil
}
} else {
equalize(mx, 255, .995, .0005)
}
image := image.NewRGBA(image.Rect(0, 0, width, height))
// now write the values to an image, equalized by the 3rd-brightest point
for x, row := range *mx {
for y, v := range row {
val := uint8(v)
image.Set(x, y, color.RGBA{val, val * 100 / 255, val, 255})
}
}
return image
}