imgo/pixelate.go

package imgo

import (
	"image"
	"image/color"
	"image/draw"
	"math"
)

// calculateMeanAverageColorWithRect returns the mean average color of the image in given rectangle.
func (i Image) calculateMeanAverageColorWithRect(rect image.Rectangle, useSquaredAverage bool) (red, green, blue uint8) {
	var redSum float64
	var greenSum float64
	var blueSum float64

	for x := rect.Min.X; x <= rect.Max.X; x++ {
		for y := rect.Min.Y; y <= rect.Max.Y; y++ {
			pixel := i.image.At(x, y)
			col := color.RGBAModel.Convert(pixel).(color.RGBA)

			if useSquaredAverage {
				redSum += float64(col.R) * float64(col.R)
				greenSum += float64(col.G) * float64(col.G)
				blueSum += float64(col.B) * float64(col.B)
			} else {
				redSum += float64(col.R)
				greenSum += float64(col.G)
				blueSum += float64(col.B)
			}
		}
	}

	rectArea := float64((rect.Dx() + 1) * (rect.Dy() + 1))

	if useSquaredAverage {
		red = uint8(math.Round(math.Sqrt(redSum / rectArea)))
		green = uint8(math.Round(math.Sqrt(greenSum / rectArea)))
		blue = uint8(math.Round(math.Sqrt(blueSum / rectArea)))
	} else {
		red = uint8(math.Round(redSum / rectArea))
		green = uint8(math.Round(greenSum / rectArea))
		blue = uint8(math.Round(blueSum / rectArea))
	}

	return
}

// pixelate apply pixelation filter to the image in given rectangle.
func (i *Image) pixelate(size int, rectangle image.Rectangle) *Image {
	bg := image.NewRGBA(i.image.Bounds())
	draw.Draw(bg, bg.Bounds(), i.image, i.image.Bounds().Min, draw.Over)

	for x := rectangle.Min.X; x < rectangle.Max.X; x += size {
		for y := rectangle.Min.Y; y < rectangle.Max.Y; y += size {
			rect := image.Rect(x, y, x+size, y+size)

			if rect.Max.X > i.width {
				rect.Max.X = i.width
			}
			if rect.Max.Y > i.height {
				rect.Max.Y = i.height
			}

			r, g, b := i.calculateMeanAverageColorWithRect(rect, true)
			col := color.RGBA{R: r, G: g, B: b, A: 255}

			for x2 := rect.Min.X; x2 < rect.Max.X; x2++ {
				for y2 := rect.Min.Y; y2 < rect.Max.Y; y2++ {
					bg.Set(x2, y2, col)
				}
			}
		}
	}

	i.image = bg
	return i
}

// Pixelate apply pixelation filter to the image.
// size is the size of the pixel.
func (i *Image) Pixelate(size int) *Image {
	if i.Error != nil {
		return i
	}

	if size <= 1 {
		return i
	}

	if i.width > i.height {
		if size > i.width {
			size = i.width
		}
	} else {
		if size > i.height {
			size = i.height
		}
	}

	return i.pixelate(size, i.image.Bounds())
}

// Mosaic apply mosaic filter to the image in given rectangle that
// (x1, y1) and (x2, y2) are the top-left and bottom-right coordinates of the rectangle.
// size is the size of the pixel.
func (i *Image) Mosaic(size, x1, y1, x2, y2 int) *Image {
	if i.Error != nil {
		return i
	}

	if x1 < 0 {
		x1 = 0
	}
	if y1 < 0 {
		y1 = 0
	}
	if x2 > i.width {
		x2 = i.width
	}
	if y2 > i.height {
		y2 = i.height
	}

	return i.pixelate(size, image.Rect(x1, y1, x2, y2))
}