func runGreyscale(cmd *Command, args []string) {
i := utils.ReadStdin()
if greyscaleAverage {
i = greyscale.Average(i)
} else if greyscaleLightness {
i = greyscale.Lightness(i)
} else if greyscaleLuminosity {
i = greyscale.Luminosity(i)
} else if greyscaleMaximal {
i = greyscale.Maximal(i)
} else if greyscaleMinimal {
i = greyscale.Minimal(i)
} else if greyscaleRed {
i = greyscale.Red(i)
} else if greyscaleGreen {
i = greyscale.Green(i)
} else if greyscaleBlue {
i = greyscale.Blue(i)
} else {
i = greyscale.Photoshop(i)
}
utils.WriteStdout(i)
}
// 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)
}