Add extract multiple channels

anthonynsimon · Jul 30, 2019 · 6defcc6 · 6defcc6
1 parent eee9188
commit 6defcc6
Show file tree

Hide file tree

Showing 2 changed files with 171 additions and 0 deletions.
diff --git a/channel/channel.go b/channel/channel.go
@@ -20,6 +20,59 @@ const (
 	Alpha
 )
 
+var (
+	allChannels = []Channel{Red, Green, Blue, Alpha}
+)
+
+// ExtractMultiple returns a RGBA image containing the values of the selected channels.
+//
+// Usage example:
+//
+//      result := channel.ExtractMultiple(img, channel.Blue, channel.Alpha)
+//
+func ExtractMultiple(img image.Image, channels ...Channel) *image.RGBA {
+	for _, c := range channels {
+		if c < 0 || 3 < c {
+			panic(fmt.Sprintf("channel index '%v' out of bounds. Red: 0, Green: 1, Blue: 2, Alpha: 3", c))
+		}
+	}
+
+	dst := clone.AsRGBA(img)
+	bounds := dst.Bounds()
+	dstW, dstH := bounds.Dx(), bounds.Dy()
+
+	if bounds.Empty() {
+		return &image.RGBA{}
+	}
+
+	channelsToRemove := []Channel{}
+	for _, channel := range allChannels {
+		shouldRemove := true
+		for _, enabled := range channels {
+			if enabled == channel {
+				shouldRemove = false
+				break
+			}
+		}
+		if shouldRemove {
+			channelsToRemove = append(channelsToRemove, channel)
+		}
+	}
+
+	parallel.Line(dstH, func(start, end int) {
+		for y := start; y < end; y++ {
+			for x := 0; x < dstW; x++ {
+				pos := y*dst.Stride + x*4
+				for _, c := range channelsToRemove {
+					dst.Pix[pos+int(c)] = 0x00
+				}
+			}
+		}
+	})
+
+	return dst
+}
+
 // Extract returns a grayscale image containing the values of the selected channel.
 //
 // Usage example:

diff --git a/channel/channel_test.go b/channel/channel_test.go
@@ -7,6 +7,124 @@ import (
 	"github.com/anthonynsimon/bild/util"
 )
 
+func TestExtractMultiple(t *testing.T) {
+	cases := []struct {
+		description string
+		channels    []Channel
+		img         image.Image
+		expected    *image.RGBA
+	}{
+		{
+			description: "red empty image",
+			channels:    []Channel{Red},
+			img:         &image.RGBA{},
+			expected:    &image.RGBA{},
+		},
+		{
+			description: "red empty pix",
+			channels:    []Channel{Red},
+			img: &image.RGBA{
+				Rect:   image.Rect(0, 0, 0, 0),
+				Stride: 0 * 4,
+				Pix:    []uint8{},
+			},
+			expected: &image.RGBA{},
+		},
+		{
+			description: "red single pixel",
+			channels:    []Channel{Red},
+			img: &image.RGBA{
+				Rect:   image.Rect(0, 0, 1, 1),
+				Stride: 1 * 4,
+				Pix: []uint8{
+					0x20, 0x60, 0x90, 0xFF,
+				},
+			},
+			expected: &image.RGBA{
+				Rect:   image.Rect(0, 0, 1, 1),
+				Stride: 1,
+				Pix: []uint8{
+					0x20, 0x00, 0x00, 0x00,
+				}},
+		},
+		{
+			description: "green single pixel",
+			channels:    []Channel{Green},
+			img: &image.RGBA{
+				Rect:   image.Rect(0, 0, 1, 1),
+				Stride: 1 * 4,
+				Pix: []uint8{
+					0x20, 0x60, 0x90, 0xFF,
+				},
+			},
+			expected: &image.RGBA{
+				Rect:   image.Rect(0, 0, 1, 1),
+				Stride: 1,
+				Pix: []uint8{
+					0x00, 0x60, 0x00, 0x00,
+				}},
+		},
+		{
+			description: "blue single pixel",
+			channels:    []Channel{Blue},
+			img: &image.RGBA{
+				Rect:   image.Rect(0, 0, 1, 1),
+				Stride: 1 * 4,
+				Pix: []uint8{
+					0x20, 0x60, 0x90, 0xFF,
+				},
+			},
+			expected: &image.RGBA{
+				Rect:   image.Rect(0, 0, 1, 1),
+				Stride: 1,
+				Pix: []uint8{
+					0x00, 0x00, 0x90, 0x00,
+				}},
+		},
+		{
+			description: "alpha single pixel",
+			channels:    []Channel{Alpha},
+			img: &image.RGBA{
+				Rect:   image.Rect(0, 0, 1, 1),
+				Stride: 1 * 4,
+				Pix: []uint8{
+					0x20, 0x60, 0x90, 0xFF,
+				},
+			},
+			expected: &image.RGBA{
+				Rect:   image.Rect(0, 0, 1, 1),
+				Stride: 1,
+				Pix: []uint8{
+					0x00, 0x00, 0x00, 0xFF,
+				}},
+		},
+		{
+			description: "multiple single pixel",
+			channels:    []Channel{Red, Alpha},
+			img: &image.RGBA{
+				Rect:   image.Rect(0, 0, 1, 1),
+				Stride: 1 * 4,
+				Pix: []uint8{
+					0x20, 0x60, 0x90, 0xFF,
+				},
+			},
+			expected: &image.RGBA{
+				Rect:   image.Rect(0, 0, 1, 1),
+				Stride: 1,
+				Pix: []uint8{
+					0x20, 0x00, 0x00, 0xFF,
+				}},
+		},
+	}
+
+	for _, c := range cases {
+		actual := ExtractMultiple(c.img, c.channels...)
+		if !util.RGBAImageEqual(actual, c.expected) {
+			t.Errorf("%s: expected: %#v, actual %#v", "Extract "+c.description, c.expected, actual)
+		}
+	}
+}
+
 func TestExtract(t *testing.T) {
 	cases := []struct {
 		description string