func runBlur(cmd *Command, args []string) {
if _, ok := styleNames[blurStyle]; !ok {
utils.Warn("--style must be one of 'clamp', 'ignore' or 'wrap'")
os.Exit(2)
}
style, _ := styleNames[blurStyle]
i := utils.ReadStdin()
if blurBox {
i = blur.Box(i, blurRadius, style)
} else {
i = blur.Gaussian(i, blurRadius, blurGaussian, style)
}
utils.WriteStdout(i)
}
// UnsharpMask sharpens the given Image using the unsharp mask technique.
// Basically the image is blurred, then subtracted from the original for
// differences above the threshold value.
func UnsharpMask(in image.Image, radius int, sigma, amount, threshold float64) image.Image {
blurred := blur.Gaussian(in, radius, sigma, blur.IGNORE)
bounds := in.Bounds()
out := image.NewRGBA(bounds)
// Absolute difference between a and b, returns float64 between 0 and 1.
diff := func(a, b float64) float64 {
if a > b {
return a - b
}
return b - a
}
for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
for x := bounds.Min.X; x < bounds.Max.X; x++ {
ar, ag, ab, aa := utils.RatioRGBA(in.At(x, y))
br, bg, bb, _ := utils.RatioRGBA(blurred.At(x, y))
if diff(ar, br) >= threshold {
ar = amount*(ar-br) + ar
}
if diff(ag, bg) >= threshold {
ag = amount*(ag-bg) + ag
}
if diff(ab, bb) >= threshold {
ab = amount*(ab-bb) + ab
}
out.Set(x, y, color.NRGBA{
uint8(utils.Truncatef(ar * 255)),
uint8(utils.Truncatef(ag * 255)),
uint8(utils.Truncatef(ab * 255)),
uint8(aa * 255),
})
}
}
return out
}