From 3ff7fa8b6462d4732ecc6cfd06bc454c36b4f6a0 Mon Sep 17 00:00:00 2001
From: Vetle Leinonen-Roeim <vetle@reprice.no>
Date: Fri, 28 Mar 2025 10:11:43 +0100
Subject: [PATCH] add trim option to image processing and implement trimEdges
 function

---
 data.go           | 11 ++++++++++-
 transform.go      | 42 ++++++++++++++++++++++++++++++++++++++++++
 transform_test.go | 19 +++++++++++++++++++
 3 files changed, 71 insertions(+), 1 deletion(-)

diff --git a/data.go b/data.go
index 0545f8b..7f4ffe7 100644
--- a/data.go
+++ b/data.go
@@ -30,6 +30,7 @@ const (
 	optCropWidth       = "cw"
 	optCropHeight      = "ch"
 	optSmartCrop       = "sc"
+	optTrim            = "trim"
 )
 
 // URLError reports a malformed URL error.
@@ -80,6 +81,9 @@ type Options struct {
 
 	// Automatically find good crop points based on image content.
 	SmartCrop bool
+
+	// If true, automatically trim pixels of the same color around the edges
+	Trim bool
 }
 
 func (o Options) String() string {
@@ -123,6 +127,9 @@ func (o Options) String() string {
 	if o.SmartCrop {
 		opts = append(opts, optSmartCrop)
 	}
+	if o.Trim {
+		opts = append(opts, optTrim)
+	}
 	sort.Strings(opts)
 	return strings.Join(opts, ",")
 }
@@ -132,7 +139,7 @@ func (o Options) String() string {
 // the presence of other fields (like Fit).  A non-empty Format value is
 // assumed to involve a transformation.
 func (o Options) transform() bool {
-	return o.Width != 0 || o.Height != 0 || o.Rotate != 0 || o.FlipHorizontal || o.FlipVertical || o.Quality != 0 || o.Format != "" || o.CropX != 0 || o.CropY != 0 || o.CropWidth != 0 || o.CropHeight != 0
+	return o.Width != 0 || o.Height != 0 || o.Rotate != 0 || o.FlipHorizontal || o.FlipVertical || o.Quality != 0 || o.Format != "" || o.CropX != 0 || o.CropY != 0 || o.CropWidth != 0 || o.CropHeight != 0 || o.Trim
 }
 
 // ParseOptions parses str as a list of comma separated transformation options.
@@ -251,6 +258,8 @@ func ParseOptions(str string) Options {
 			options.Format = opt
 		case opt == optSmartCrop:
 			options.SmartCrop = true
+		case opt == optTrim:
+			options.Trim = true
 		case strings.HasPrefix(opt, optRotatePrefix):
 			value := strings.TrimPrefix(opt, optRotatePrefix)
 			options.Rotate, _ = strconv.Atoi(value)
diff --git a/transform.go b/transform.go
index 103e20f..b9d90c9 100644
--- a/transform.go
+++ b/transform.go
@@ -309,5 +309,47 @@ func transformImage(m image.Image, opt Options) image.Image {
 		m = imaging.FlipH(m)
 	}
 
+	// trim
+	if opt.Trim {
+		m = trimEdges(m)
+	}
+
 	return m
 }
+
+func trimEdges(img image.Image) image.Image {
+	bounds := img.Bounds()
+	minX, minY, maxX, maxY := bounds.Max.X, bounds.Max.Y, bounds.Min.X, bounds.Min.Y
+
+	// Get the color of the first pixel (top-left corner)
+	baseColor := img.At(bounds.Min.X, bounds.Min.Y)
+
+	// Check each pixel and find the bounding box of non-matching pixels
+	for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
+		for x := bounds.Min.X; x < bounds.Max.X; x++ {
+			if img.At(x, y) != baseColor { // Non-matching pixel
+				if x < minX {
+					minX = x
+				}
+				if y < minY {
+					minY = y
+				}
+				if x > maxX {
+					maxX = x
+				}
+				if y > maxY {
+					maxY = y
+				}
+			}
+		}
+	}
+
+	// If no non-matching pixels are found, return the original image
+	if minX > maxX || minY > maxY {
+		return img
+	}
+
+	// Crop the image to the bounding box of non-matching pixels
+	croppedImg := imaging.Crop(img, image.Rect(minX, minY, maxX+1, maxY+1))
+	return croppedImg
+}
diff --git a/transform_test.go b/transform_test.go
index b22afab..b130ea4 100644
--- a/transform_test.go
+++ b/transform_test.go
@@ -375,3 +375,22 @@ func TestTransformImage(t *testing.T) {
 		}
 	}
 }
+
+func TestTrimBordersOfSameColor(t *testing.T) {
+	src := newImage(4, 4,
+		color.NRGBA{255, 255, 255, 255}, color.NRGBA{255, 255, 255, 255}, color.NRGBA{255, 255, 255, 255}, color.NRGBA{255, 255, 255, 255},
+		color.NRGBA{255, 255, 255, 255}, color.NRGBA{255, 0, 0, 255}, color.NRGBA{255, 0, 0, 255}, color.NRGBA{255, 255, 255, 255},
+		color.NRGBA{255, 255, 255, 255}, color.NRGBA{255, 0, 0, 255}, color.NRGBA{255, 0, 0, 255}, color.NRGBA{255, 255, 255, 255},
+		color.NRGBA{255, 255, 255, 255}, color.NRGBA{255, 255, 255, 255}, color.NRGBA{255, 255, 255, 255}, color.NRGBA{255, 255, 255, 255},
+	)
+
+	want := newImage(2, 2,
+		color.NRGBA{255, 0, 0, 255}, color.NRGBA{255, 0, 0, 255},
+		color.NRGBA{255, 0, 0, 255}, color.NRGBA{255, 0, 0, 255},
+	)
+
+	got := trimEdges(src)
+	if !reflect.DeepEqual(got, want) {
+		t.Errorf("trimEdges() = %v, want %v", got, want)
+	}
+}