feat: Add edge detection filter

.gitignore

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+assets
+image.png
+.idea

go.mod

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+module myzel394.app/image-stuff
+
+go 1.23.3
+
+require gonum.org/v1/gonum v0.15.1 // indirect

go.sum

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+gonum.org/v1/gonum v0.15.1 h1:FNy7N6OUZVUaWG9pTiD+jlhdQ3lMP+/LcTpJ6+a8sQ0=
+gonum.org/v1/gonum v0.15.1/go.mod h1:eZTZuRFrzu5pcyjN5wJhcIhnUdNijYxX1T2IcrOGY0o=

image_analyzer.go

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+package main
+
+import (
+	"image"
+	"image/color"
+	"math"
+)
+
+type ImageAnalyzer struct {
+	image.Image
+}
+
+// Calculate the energy using the dual-gradient energy function
+func getEnergy(
+	firstPixel color.Color,
+	secondPixel color.Color,
+) float64 {
+	firstRed, firstGreen, firstBlue, _ := firstPixel.RGBA()
+	firstRed, firstGreen, firstBlue = firstRed >> 8, firstGreen >> 8, firstBlue >> 8
+	secondRed, secondGreen, secondBlue, _ := secondPixel.RGBA()
+	secondRed, secondGreen, secondBlue = secondRed >> 8, secondGreen >> 8, secondBlue >> 8
+
+	return float64(
+		math.Abs(float64(firstRed - secondRed)) +
+		math.Abs(float64(firstGreen - secondGreen)) +
+		math.Abs(float64(firstBlue - secondBlue)),
+	)
+}
+
+// Calculate a 0-255 grayscale value from a color using the NTSC formula
+func colorToGray(color color.Color) float64 {
+	red, green, blue, _ := color.RGBA()
+	red, green, blue = red >> 8, green >> 8, blue >> 8
+
+	return 0.299 * float64(red) +
+		0.587 * float64(green) +
+		0.114 * float64(blue)
+}
+
+func sumSlice(slice []float64) float64 {
+	var sum float64
+	for _, value := range slice {
+		sum += value
+	}
+	return sum
+}
+
+func (image *ImageAnalyzer) CalculateEnergyAt(x int, y int) float64 {
+	northPixel := image.At(
+		x,
+		max(0, y - 1),
+	)
+	northEastPixel := image.At(
+		min(image.Bounds().Max.X, x + 1),
+		max(0, y - 1),
+	)
+	eastPixel := image.At(
+		min(image.Bounds().Max.X, x + 1),
+		y,
+	)
+	southEastPixel := image.At(
+		min(image.Bounds().Max.X, x + 1),
+		min(image.Bounds().Max.Y, y + 1),
+	)
+	southPixel := image.At(
+		x,
+		min(image.Bounds().Max.Y, y + 1),
+	)
+	southWestPixel := image.At(
+		max(0, x - 1),
+		min(image.Bounds().Max.Y, y + 1),
+	)
+	westPixel := image.At(
+		max(0, x - 1),
+		y,
+	)
+	northWestPixel := image.At(
+		max(0, x - 1),
+		max(0, y - 1),
+	)
+
+	thisPixel := image.At(
+		x,
+		y,
+	)
+
+	_ = thisPixel
+	_ = northPixel
+	_ = northEastPixel
+	_ = southPixel
+
+	horizontalMatrix := []float64{
+		colorToGray(northWestPixel), 0, -colorToGray(northEastPixel),
+		2 * colorToGray(westPixel), 0, -2 * colorToGray(eastPixel),
+		colorToGray(southWestPixel), 0, -colorToGray(southEastPixel),
+	}
+	verticalMatrix := []float64{
+		colorToGray(northWestPixel), 2 * colorToGray(northPixel), colorToGray(northEastPixel),
+		0, 0, 0,
+		-colorToGray(southWestPixel), -2 * colorToGray(southPixel), -colorToGray(southEastPixel),
+	}
+
+	g_x := sumSlice(horizontalMatrix)
+	g_y := sumSlice(verticalMatrix)
+
+	return math.Sqrt(
+		math.Pow(g_x, 2) +
+		math.Pow(g_y, 2),
+	)
+}

main.go

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+package main
+
+import (
+	"image"
+	"image/color"
+	"image/png"
+	_ "image/png"
+	"os"
+)
+
+func main() {
+	// Read image
+	reader, _ := os.Open("./assets/surfer.png")
+	rawImage, _, _ := image.Decode(reader)
+	readImage := ImageAnalyzer{Image: rawImage}
+
+	bounds := readImage.Bounds()
+	width := bounds.Max.X
+	height := bounds.Max.Y
+	writeImage := image.NewRGBA(bounds)
+
+	// Main action
+	for x := range width {
+		for y := range height {
+			energy := uint8(readImage.CalculateEnergyAt(x, y))
+
+			color := color.RGBA{energy, energy, energy, 255}
+			writeImage.Set(x, y, color)
+		}
+	}
+
+	// Out image
+	writer, _ := os.Create("image.png")
+	png.Encode(writer, writeImage)
+}