Fix grayscale on sub-images (#4)

grayscale/grayscale.go

@@ -1,17 +1,19 @@
 package grayscale
 
 import (
-	"github.com/ernyoke/imger/utils"
 	"image"
 	"image/color"
+
+	"github.com/ernyoke/imger/utils"
 )
 
 // Grayscale takes an image on any type and returns the equivalent grayscale image represented on 8 bits.
 func Grayscale(img image.Image) *image.Gray {
 	gray := image.NewGray(img.Bounds())
 	size := img.Bounds().Size()
+	offset := img.Bounds().Min
 	utils.ParallelForEachPixel(size, func(x, y int) {
-		gray.Set(x, y, color.GrayModel.Convert(img.At(x, y)))
+		gray.Set(x+offset.X, y+offset.Y, color.GrayModel.Convert(img.At(x+offset.X, y+offset.Y)))
 	})
 	return gray
 }
@@ -20,8 +22,9 @@ func Grayscale(img image.Image) *image.Gray {
 func Grayscale16(img image.Image) *image.Gray16 {
 	gray := image.NewGray16(img.Bounds())
 	size := img.Bounds().Size()
+	offset := img.Bounds().Min
 	utils.ParallelForEachPixel(size, func(x, y int) {
-		gray.Set(x, y, color.Gray16Model.Convert(img.At(x, y)))
+		gray.Set(x+offset.X, y+offset.Y, color.Gray16Model.Convert(img.At(x+offset.X, y+offset.Y)))
 	})
 	return gray
 }

grayscale/grayscale_test.go

@@ -1,9 +1,10 @@
 package grayscale
 
 import (
-	"github.com/ernyoke/imger/imgio"
 	"image"
 	"testing"
+
+	"github.com/ernyoke/imger/imgio"
 )
 
 // -----------------------------Acceptance tests------------------------------------
@@ -29,10 +30,24 @@ func Test_Acceptance_GrayScale(t *testing.T) {
 	tearDownTestCase(t, gray, "../res/grayscale/gray.jpg")
 }
 
+func Test_Acceptance_GrayScaleCropped(t *testing.T) {
+	rgba := setupTestCaseRGBA(t)
+	cropped := rgba.SubImage(image.Rect(100, 100, rgba.Bounds().Max.X-100, rgba.Bounds().Max.Y-100))
+	gray := Grayscale(cropped)
+	tearDownTestCase(t, gray, "../res/grayscale/cropped_gray.jpg")
+}
+
 func Test_Acceptance_GrayScale16(t *testing.T) {
 	rgba := setupTestCaseRGBA(t)
 	gray := Grayscale16(rgba)
 	tearDownTestCase(t, gray, "../res/grayscale/gray16.jpg")
 }
 
+func Test_Acceptance_GrayScale16Cropped(t *testing.T) {
+	rgba := setupTestCaseRGBA(t)
+	cropped := rgba.SubImage(image.Rect(100, 100, rgba.Bounds().Max.X-100, rgba.Bounds().Max.Y-100))
+	gray := Grayscale16(cropped)
+	tearDownTestCase(t, gray, "../res/grayscale/cropped_gray16.jpg")
+}
+
 // ---------------------------------------------------------------------------------