// Extract real parts, copy them from src to dst.
// In the meanwhile, check if imaginary parts are nearly zero
// and scale the kernel to compensate for unnormalized FFTs.
func scaleRealParts(dst, src *data.Slice, scale float32) {
util.Argument(2*dst.Len() == src.Len())
util.Argument(dst.NComp() == 1 && src.NComp() == 1)
srcList := src.HostCopy().Host()[0]
dstList := dst.Host()[0]
// Normally, the FFT'ed kernel is purely real because of symmetry,
// so we only store the real parts...
maximg := float32(0.)
maxreal := float32(0.)
for i := 0; i < src.Len()/2; i++ {
dstList[i] = srcList[2*i] * scale
if fabs(srcList[2*i+0]) > maxreal {
maxreal = fabs(srcList[2*i+0])
}
if fabs(srcList[2*i+1]) > maximg {
maximg = fabs(srcList[2*i+1])
}
}
// ...however, we check that the imaginary parts are nearly zero,
// just to be sure we did not make a mistake during kernel creation.
if maximg/maxreal > FFT_IMAG_TOLERANCE {
log.Fatalf("Too large FFT kernel imaginary/real part: %v", maximg/maxreal)
}
}
func Image(f *data.Slice, fmin, fmax string) *image.NRGBA {
dim := f.NComp()
switch dim {
default:
log.Fatalf("unsupported number of components: %v", dim)
case 3:
return drawVectors(f.Vectors())
case 1:
min, max := extrema(f.Host()[0])
if fmin != "auto" {
m, err := strconv.ParseFloat(fmin, 32)
util.FatalErr(err)
min = float32(m)
}
if fmax != "auto" {
m, err := strconv.ParseFloat(fmax, 32)
util.FatalErr(err)
max = float32(m)
}
return drawFloats(f.Scalars(), min, max)
}
panic("unreachable")
}