// cb is backdrop colour, cs is source (blend layer) colour
func BlendPixel(cb, cs color.Color, f Blender) color.Color {
// Uses methods described in "PDF Reference, Third Edition" from Adobe
// see: http://www.adobe.com/devnet/pdf/pdf_reference_archive.html
// 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)
return color.RGBA{
uint8(utils.Truncatef(red * 255)),
uint8(utils.Truncatef(green * 255)),
uint8(utils.Truncatef(blue * 255)),
uint8(utils.Truncatef(alpha * 255)),
}
}
// 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
}
// Lighter chooses the lightest colour by comparing the sum of the colour
// channels.
func Lighter(a, b image.Image) image.Image {
return BlendPixels(a, b, func(c, d color.Color) color.Color {
i, j, k, _ := utils.RatioRGBA(c)
m, n, o, _ := utils.RatioRGBA(d)
if i+j+k > m+n+o {
return c
}
return d
})
}
// Dodge brightens the base colour to reflect the blend colour.
func Dodge(a, b image.Image) image.Image {
return BlendPixels(a, b, func(c, d color.Color) color.Color {
i, j, k, l := utils.RatioRGBA(c)
m, n, o, p := utils.RatioRGBA(d)
r := i / (1 - m)
g := j / (1 - n)
b := k / (1 - o)
a := p + l*(1-p)
return ratioNRGBA(r, g, b, a)
})
}
// Screen multiplies the complements of the base and blend colour channel
// values, then complements the result.
func Screen(a, b image.Image) image.Image {
return BlendPixels(a, b, func(c, d color.Color) color.Color {
i, j, k, l := utils.RatioRGBA(c)
m, n, o, p := utils.RatioRGBA(d)
r := 1 - ((1 - i) * (1 - m))
g := 1 - ((1 - j) * (1 - n))
b := 1 - ((1 - k) * (1 - o))
a := p + l*(1-p)
return ratioNRGBA(r, g, b, a)
})
}
// Lightne selects the lighter of each pixels' colour channels.
func Lighten(a, b image.Image) image.Image {
return BlendPixels(a, b, func(c, d color.Color) color.Color {
i, j, k, l := utils.RatioRGBA(c)
m, n, o, p := utils.RatioRGBA(d)
r := utils.Maxf(i, m)
g := utils.Maxf(j, n)
b := utils.Maxf(k, o)
a := utils.Maxf(l, p)
return ratioNRGBA(r, g, b, a)
})
}
// LinearBurn adds the values of each colour channel together, then subtracts
// white to produce a darker image.
func LinearBurn(a, b image.Image) image.Image {
return BlendPixels(a, b, func(c, d color.Color) color.Color {
i, j, k, l := utils.RatioRGBA(c)
m, n, o, p := utils.RatioRGBA(d)
r := i + m - 1
g := j + n - 1
b := k + o - 1
a := p + l*(1-p)
return ratioNRGBA(r, g, b, a)
})
}
// Burn darkens the base colour to reflect the blend colour.
func Burn(a, b image.Image) image.Image {
return BlendPixels(a, b, func(c, d color.Color) color.Color {
i, j, k, l := utils.RatioRGBA(c)
m, n, o, p := utils.RatioRGBA(d)
r := 1 - ((1 - i) / m)
g := 1 - ((1 - j) / n)
b := 1 - ((1 - k) / o)
a := p + l*(1-p)
return ratioNRGBA(r, g, b, a)
})
}
// Multiply multiplies the base and blend image colour channels.
func Multiply(a, b image.Image) image.Image {
return BlendPixels(a, b, func(c, d color.Color) color.Color {
i, j, k, l := utils.RatioRGBA(c)
m, n, o, p := utils.RatioRGBA(d)
r := i * m
g := j * n
b := k * o
a := l * p
return ratioNRGBA(r, g, b, a)
})
}
// Exclusion creates an effect similar to, but lower in contrast than,
// difference.
func Exclusion(a, b image.Image) image.Image {
return BlendPixels(a, b, func(c, d color.Color) color.Color {
i, j, k, l := utils.RatioRGBA(c)
m, n, o, p := utils.RatioRGBA(d)
r := m + i - (2 * m * i)
g := n + j - (2 * n * j)
b := o + k - (2 * o * k)
a := p + l*(1-p)
return ratioNRGBA(r, g, b, a)
})
}
// Difference finds the absolute difference between the base and blend colours.
func Difference(a, b image.Image) image.Image {
return BlendPixels(a, b, func(c, d color.Color) color.Color {
i, j, k, l := utils.RatioRGBA(c)
m, n, o, p := utils.RatioRGBA(d)
r := math.Abs(m - i)
g := math.Abs(n - j)
b := math.Abs(o - k)
a := p + l*(1-p)
return ratioNRGBA(r, g, b, 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
}
// HardMix adds the red, green and blue channel values of the blend colour to
// the RGB values of the base colour. It sets any values greater than 255 to
// 255, and anything less to 0. This therefore makes all pixels either red,
// green, blue, white or black.
func HardMix(a, b image.Image) image.Image {
return BlendPixels(a, b, func(c, d color.Color) color.Color {
i, j, k, l := utils.RatioRGBA(c)
m, n, o, p := utils.RatioRGBA(d)
f := func(i, j float64) float64 {
if j < 1-i {
return 0
}
return 1
}
r := f(i, m)
g := f(j, n)
b := f(k, o)
a := p + l*(1-p)
return ratioNRGBA(r, g, b, a)
})
}
// LinearLight lightens or darkens the image by changing the brightness. If the
// blend colour is lighter, the image is lightened; if the blend colour is
// darker, the image is darkened. It uses linear burn and linear dodge to darken
// or lighten.
func LinearLight(a, b image.Image) image.Image {
return BlendPixels(a, b, func(c, d color.Color) color.Color {
i, j, k, l := utils.RatioRGBA(c)
m, n, o, p := utils.RatioRGBA(d)
f := func(i, j float64) float64 {
if j > 0.5 {
return i + 2*(j-0.5)
}
return i + 2*j - 1
}
r := f(i, m)
g := f(j, n)
b := f(k, o)
a := p + l*(1-p)
return ratioNRGBA(r, g, b, a)
})
}
// VividLight combines Dodge and Burn. Dodge applies to lighter colours, and
// Burn to darker.
func VividLight(a, b image.Image) image.Image {
return BlendPixels(a, b, func(c, d color.Color) color.Color {
i, j, k, l := utils.RatioRGBA(c)
m, n, o, p := utils.RatioRGBA(d)
f := func(i, j float64) float64 {
if j > 0.5 {
return i / (2 * (1 - j))
}
return 1 - (1-i)/(2*j)
}
r := f(i, m)
g := f(j, n)
b := f(k, o)
a := p + l*(1-p)
return ratioNRGBA(r, g, b, a)
})
}
func AdjustC(value float64) utils.Composable {
return func(c color.Color) color.Color {
r, g, b, a := utils.RatioRGBA(c)
r = utils.Truncatef(math.Pow(r, 1/value) * 255)
g = utils.Truncatef(math.Pow(g, 1/value) * 255)
b = utils.Truncatef(math.Pow(b, 1/value) * 255)
return color.NRGBA{uint8(r), uint8(g), uint8(b), uint8(a * 255)}
}
}
// 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
}
func AlphaC(adj utils.Adjuster) utils.Composable {
return func(c color.Color) color.Color {
r, g, b, a := utils.RatioRGBA(c)
a = adj(a)
if a > 1 {
a = 1
} else if a < 0 {
a = 0
}
return color.NRGBA{uint8(r * 255), uint8(g * 255), uint8(b * 255), uint8(a * 255)}
}
}
func BlueC(adj utils.Adjuster) utils.Composable {
return func(c color.Color) color.Color {
r, g, b, a := utils.RatioRGBA(c)
b = adj(b)
if b > 1 {
b = 1
} else if b < 0 {
b = 0
}
return color.NRGBA{uint8(r * 255), uint8(g * 255), uint8(b * 255), uint8(a * 255)}
}
}
func GreenC(adj utils.Adjuster) utils.Composable {
return func(c color.Color) color.Color {
r, g, b, a := utils.RatioRGBA(c)
g = adj(g)
if g > 1 {
g = 1
} else if g < 0 {
g = 0
}
return color.NRGBA{uint8(r * 255), uint8(g * 255), uint8(b * 255), uint8(a * 255)}
}
}
func RedC(adj utils.Adjuster) utils.Composable {
return func(c color.Color) color.Color {
r, g, b, a := utils.RatioRGBA(c)
r = adj(r)
if r > 1 {
r = 1
} else if r < 0 {
r = 0
}
return color.NRGBA{uint8(r * 255), uint8(g * 255), uint8(b * 255), uint8(a * 255)}
}
}
func AdjustC(value float64) utils.Composable {
return func(c color.Color) color.Color {
r, g, b, a := utils.RatioRGBA(c)
r = utils.Truncatef((((r - 0.5) * value) + 0.5) * 255)
g = utils.Truncatef((((g - 0.5) * value) + 0.5) * 255)
b = utils.Truncatef((((b - 0.5) * value) + 0.5) * 255)
a = a * 255
return color.NRGBA{uint8(r), uint8(g), uint8(b), uint8(a)}
}
}
// PinLight replaces the colours, depending on the blend colour.
func PinLight(a, b image.Image) image.Image {
return BlendPixels(a, b, func(c, d color.Color) color.Color {
i, j, k, l := utils.RatioRGBA(c)
m, n, o, p := utils.RatioRGBA(d)
f := func(i, j float64) float64 {
if i < 2*j-1 {
return 2*j - 1
} else if i > 2*j {
return 2 * j
}
return i
}
r := f(i, m)
g := f(j, n)
b := f(k, o)
a := p + l*(1-p)
return ratioNRGBA(r, g, b, a)
})
}
func hsiaModel(c color.Color) color.Color {
if _, ok := c.(HSIA); ok {
return c
}
r, g, b, a := utils.RatioRGBA(c)
maxi := utils.Maxf(r, g, b)
mini := utils.Minf(r, g, b)
chroma := maxi - mini
// Work out hue
hdash := 0.0
if chroma == 0 {
hdash = 0
} else if maxi == r {
hdash = math.Mod((g-b)/chroma, 6)
} else if maxi == g {
hdash = (b-r)/chroma + 2.0
} else if maxi == b {
hdash = (r-g)/chroma + 4.0
}
hue := hdash * 60
if chroma == 0 {
hue = 0
}
// Work out intensity
intensity := (r + g + b) / 3
// Work out saturation
saturation := 0.0
if chroma != 0 {
saturation = 1 - mini/intensity
}
// prefer positive hues
if hue < 0 {
hue += 360
}
return HSIA{hue, saturation, intensity, a}
}
func hsvaModel(c color.Color) color.Color {
if _, ok := c.(HSVA); ok {
return c
}
r, g, b, a := utils.RatioRGBA(c)
maxi := utils.Maxf(r, g, b)
mini := utils.Minf(r, g, b)
chroma := maxi - mini
// Work out hue
hdash := 0.0
if chroma == 0 {
hdash = 0
} else if maxi == r {
hdash = math.Mod((g-b)/chroma, 6)
} else if maxi == g {
hdash = (b-r)/chroma + 2.0
} else if maxi == b {
hdash = (r-g)/chroma + 4.0
}
hue := hdash * 60
if chroma == 0 {
hue = 0
}
// Work out value
value := maxi
// Work out saturation
saturation := 0.0
if chroma != 0 {
saturation = chroma / value
}
return HSVA{hue, saturation, value, a}
}
func hslaModel(c color.Color) color.Color {
if _, ok := c.(HSLA); ok {
return c
}
r, g, b, a := utils.RatioRGBA(c)
maxi := utils.Maxf(r, g, b)
mini := utils.Minf(r, g, b)
chroma := maxi - mini
// Work out hue
hdash := 0.0
if chroma == 0 {
hdash = 0
} else if maxi == r {
hdash = math.Mod((g-b)/chroma, 6)
} else if maxi == g {
hdash = (b-r)/chroma + 2.0
} else if maxi == b {
hdash = (r-g)/chroma + 4.0
}
hue := hdash * 60
if chroma == 0 {
hue = 0
}
// Work out lightness
lightness := 0.5 * (maxi + mini)
// Work out saturation
saturation := 0.0
if chroma != 0 {
saturation = chroma / (1 - math.Abs(2*lightness-1))
}
return HSLA{hue, saturation, lightness, a}
}
func SigmoidalC(factor, midpoint float64) utils.Composable {
alpha := midpoint
beta := factor
f := func(u float64) float64 {
return (1.0/(1.0+math.Exp(beta*(alpha-u))) -
1.0/(1.0+math.Exp(beta))) /
(1.0/(1.0+math.Exp(beta*(alpha-1))) -
1.0/(1.0+math.Exp(beta*alpha)))
}
return func(c color.Color) color.Color {
r, g, b, a := utils.RatioRGBA(c)
r = utils.Truncatef(f(r) * 255)
g = utils.Truncatef(f(g) * 255)
b = utils.Truncatef(f(b) * 255)
a = a * 255
return color.NRGBA{uint8(r), uint8(g), uint8(b), uint8(a)}
}
}
func getAlpha(c color.Color) float64 {
_, _, _, a := utils.RatioRGBA(c)
return a
}
func getBlue(c color.Color) float64 {
_, _, b, _ := utils.RatioRGBA(c)
return b
}
func getGreen(c color.Color) float64 {
_, g, _, _ := utils.RatioRGBA(c)
return g
}