// Dissolve randomly selects pixels from the blend image, depending on their
// opacity. Blend pixels with higher opacities are more likely to be displayed.
func Dissolve(a, b image.Image) image.Image {
ba := a.Bounds()
bb := b.Bounds()
width := int(utils.Min(uint32(ba.Dx()), uint32(bb.Dx())))
height := int(utils.Min(uint32(ba.Dy()), uint32(bb.Dy())))
result := image.NewRGBA(image.Rect(0, 0, width, height))
for y := 0; y < height; y++ {
for x := 0; x < width; x++ {
// base colour
rb, gb, bb, ab := utils.RatioRGBA(a.At(x, y))
// blend colour
rs, gs, bs, as := utils.RatioRGBA(b.At(x, y))
toPaint := ratioNRGBA(rb, gb, bb, ab)
if rand.Float64() < as {
toPaint = ratioNRGBA(rs, gs, bs, 1)
}
result.Set(x, y, toPaint)
}
}
return result
}
// 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)}
})
}
// BlendPixels takes the base and blend images and applies the given Blender to
// each of their pixel pairs.
func BlendPixels(a, b image.Image, f Blender) image.Image {
ba := a.Bounds()
bb := b.Bounds()
width := int(utils.Min(uint32(ba.Dx()), uint32(bb.Dx())))
height := int(utils.Min(uint32(ba.Dy()), uint32(bb.Dy())))
result := image.NewRGBA(image.Rect(0, 0, width, height))
for y := 0; y < height; y++ {
for x := 0; x < width; x++ {
// Uses methods described in "PDF Reference, Third Edition" from Adobe
// see: http://www.adobe.com/devnet/pdf/pdf_reference_archive.html
// backdrop colour
cb := a.At(x, y)
// source colour
cs := b.At(x, y)
// result colour
cr := f(cb, cs)
rb, gb, bb, ab := utils.RatioRGBA(cb)
rs, gs, bs, as := utils.RatioRGBA(cs)
rr, gr, br, _ := utils.RatioRGBA(cr)
// Color compositing formula, expanded form. (Section 7.2.5)
red := ((1 - as) * ab * rb) + ((1 - ab) * as * rs) + (ab * as * rr)
green := ((1 - as) * ab * gb) + ((1 - ab) * as * gs) + (ab * as * gr)
blue := ((1 - as) * ab * bb) + ((1 - ab) * as * bs) + (ab * as * br)
// Union function. (Section 7.2.6)
alpha := ab + as - (ab * as)
result.Set(x, y, color.RGBA{
uint8(utils.Truncatef(red * 255)),
uint8(utils.Truncatef(green * 255)),
uint8(utils.Truncatef(blue * 255)),
uint8(utils.Truncatef(alpha * 255)),
})
}
}
return result
}
func MinimalC() utils.Composable {
return colorAlterer(func(r, g, b uint32) uint32 {
return utils.Min(r, g, b)
})
}
func LightnessC() utils.Composable {
return colorAlterer(func(r, g, b uint32) uint32 {
return (utils.Max(r, g, b) + utils.Min(r, g, b)) / 2
})
}