// Addition adds the blend colour to the base colour. (aka. Linear Dodge)
func Addition(a, b image.Image) image.Image {
return BlendPixels(a, b, func(c, d color.Color) color.Color {
i, j, k, l := utils.NormalisedRGBA(c)
m, n, o, p := utils.NormalisedRGBA(d)
r := utils.Min(i+m, 255)
g := utils.Min(j+n, 255)
b := utils.Min(k+o, 255)
a := utils.Min(l+p, 255)
return color.NRGBA{uint8(r), uint8(g), uint8(b), uint8(a)}
})
}
func colorAlterer(f pixelAlterer) utils.Composable {
return func(c color.Color) color.Color {
r, g, b, a := utils.NormalisedRGBA(c)
grey := uint8(f(r, g, b))
return color.NRGBA{grey, grey, grey, uint8(a)}
}
}
// Fade changes the opacity of the Image given by the amount given. The
// resulting opacity is the product of the image's opacity and the amount, so a
// value of 1 has no effect whilst a value of 0 makes the image fully
// transparent.
func Fade(img image.Image, amount float64) image.Image {
f := func(c color.Color) color.Color {
r, g, b, a := utils.NormalisedRGBA(c)
return color.NRGBA{
uint8(float64(r)),
uint8(float64(g)),
uint8(float64(b)),
uint8(float64(a) * amount),
}
}
return utils.MapColor(img, f)
}
// Subtraction subtracts the blend colour from the base colour.
func Subtraction(a, b image.Image) image.Image {
return BlendPixels(a, b, func(c, d color.Color) color.Color {
i, j, k, l := utils.NormalisedRGBA(c)
m, n, o, p := utils.NormalisedRGBA(d)
r := utils.Truncate(i - m)
g := utils.Truncate(j - n)
b := utils.Truncate(k - o)
if m > i {
r = 0
}
if n > j {
g = 0
}
if o > k {
b = 0
}
a := p + l*(1-p)
return color.NRGBA{uint8(r), uint8(g), uint8(b), uint8(a)}
})
}
// Auto calculates the mean values of an image, then applies a gamma adjustment
// so that the mean colour in the image has a value of half.
func Auto(img image.Image) image.Image {
luma := greyscale.Luminosity(img)
greys := []uint32{}
b := luma.Bounds()
for y := b.Min.Y; y < b.Max.Y; y++ {
for x := b.Min.X; x < b.Max.X; x++ {
g, _, _, _ := utils.NormalisedRGBA(luma.At(x, y))
greys = append(greys, g)
}
}
var averageGrey uint32 = 0
for i := 0; i < len(greys); i++ {
averageGrey += greys[i]
}
averageGrey /= uint32(len(greys))
newGamma := 127.5 / float64(averageGrey)
return Adjust(img, newGamma)
}
func setAlpha(c color.Color, v float64) color.Color {
r, g, b, _ := utils.NormalisedRGBA(c)
v = utils.Truncatef(255 * v)
return color.NRGBA{uint8(r), uint8(g), uint8(b), uint8(v)}
}
func setBlue(c color.Color, v float64) color.Color {
r, g, _, a := utils.NormalisedRGBA(c)
v = utils.Truncatef(255 * v)
return color.NRGBA{uint8(r), uint8(g), uint8(v), uint8(a)}
}
func setGreen(c color.Color, v float64) color.Color {
r, _, b, a := utils.NormalisedRGBA(c)
v = utils.Truncatef(255 * v)
return color.NRGBA{uint8(r), uint8(v), uint8(b), uint8(a)}
}
func setRed(c color.Color, v float64) color.Color {
_, g, b, a := utils.NormalisedRGBA(c)
v = utils.Truncatef(255 * v)
return color.NRGBA{uint8(v), uint8(g), uint8(b), uint8(a)}
}