add smartcrop feature

fixes #55

README.md

@@ -71,6 +71,10 @@ image][material-animation] resized to 200px square and rotated 270 degrees:
 
 <a href="https://willnorris.com/api/imageproxy/200,r270/https://willnorris.com/2015/05/material-animations.gif"><img src="https://willnorris.com/api/imageproxy/200,r270/https://willnorris.com/2015/05/material-animations.gif" alt="200,r270"></a>
 
+The smart crop feature can best be seen by comparing the following images, with and without smart crop.
+
+<a href="https://willnorris.com/api/imageproxy/150x300/https://judahnorris.com/images/judah-sheets.jpg"><img src="https://willnorris.com/api/imageproxy/150x300/https://judahnorris.com/images/judah-sheets.jpg" alt="200x400"></a>
+<a href="https://willnorris.com/api/imageproxy/150x300,sc/https://judahnorris.com/images/judah-sheets.jpg"><img src="https://willnorris.com/api/imageproxy/150x300,sc/https://judahnorris.com/images/judah-sheets.jpg" alt="200x400,sc"></a>
 
 ## Getting Started ##
 

data.go

@@ -39,6 +39,7 @@ const (
 	optCropY           = "cy"
 	optCropWidth       = "cw"
 	optCropHeight      = "ch"
+	optSmartCrop       = "sc"
 )
 
 // URLError reports a malformed URL error.
@@ -86,6 +87,9 @@ type Options struct {
 	CropY      float64
 	CropWidth  float64
 	CropHeight float64
+
+	// Automatically find good crop points based on image content.
+	SmartCrop bool
 }
 
 func (o Options) String() string {
@@ -126,6 +130,9 @@ func (o Options) String() string {
 	if o.CropHeight != 0 {
 		opts = append(opts, fmt.Sprintf("%s%v", string(optCropHeight), o.CropHeight))
 	}
+	if o.SmartCrop {
+		opts = append(opts, optSmartCrop)
+	}
 	return strings.Join(opts, ",")
 }
 
@@ -159,6 +166,12 @@ func (o Options) transform() bool {
 // crop width or height will be adjusted, preserving the specified cx and cy
 // values.  Rectangular crop is applied before any other transformations.
 //
+// Smart Crop
+//
+// The "sc" option will perform a content-aware smart crop to fit the
+// requested image width and height dimensions (see Size and Cropping below).
+// The smart crop option will override any requested rectangular crop.
+//
 // Size and Cropping
 //
 // The size option takes the general form "{width}x{height}", where width and
@@ -246,6 +259,8 @@ func ParseOptions(str string) Options {
 			options.ScaleUp = true
 		case opt == optFormatJPEG, opt == optFormatPNG, opt == optFormatTIFF:
 			options.Format = opt
+		case opt == optSmartCrop:
+			options.SmartCrop = true
 		case strings.HasPrefix(opt, optRotatePrefix):
 			value := strings.TrimPrefix(opt, optRotatePrefix)
 			options.Rotate, _ = strconv.Atoi(value)

data_test.go

@@ -31,19 +31,19 @@ func TestOptions_String(t *testing.T) {
 			"0x0",
 		},
 		{
-			Options{1, 2, true, 90, true, true, 80, "", false, "", 0, 0, 0, 0},
+			Options{1, 2, true, 90, true, true, 80, "", false, "", 0, 0, 0, 0, false},
 			"1x2,fit,r90,fv,fh,q80",
 		},
 		{
-			Options{0.15, 1.3, false, 45, false, false, 95, "c0ffee", false, "png", 0, 0, 0, 0},
+			Options{0.15, 1.3, false, 45, false, false, 95, "c0ffee", false, "png", 0, 0, 0, 0, false},
 			"0.15x1.3,r45,q95,sc0ffee,png",
 		},
 		{
-			Options{0.15, 1.3, false, 45, false, false, 95, "c0ffee", false, "", 100, 200, 0, 0},
+			Options{0.15, 1.3, false, 45, false, false, 95, "c0ffee", false, "", 100, 200, 0, 0, false},
 			"0.15x1.3,r45,q95,sc0ffee,cx100,cy200",
 		},
 		{
-			Options{0.15, 1.3, false, 45, false, false, 95, "c0ffee", false, "png", 100, 200, 300, 400},
+			Options{0.15, 1.3, false, 45, false, false, 95, "c0ffee", false, "png", 100, 200, 300, 400, false},
 			"0.15x1.3,r45,q95,sc0ffee,png,cx100,cy200,cw300,ch400",
 		},
 	}
@@ -94,19 +94,19 @@ func TestParseOptions(t *testing.T) {
 		{"FOO,1,BAR,r90,BAZ", Options{Width: 1, Height: 1, Rotate: 90}},
 
 		// flags, in different orders
-		{"q70,1x2,fit,r90,fv,fh,sc0ffee,png", Options{1, 2, true, 90, true, true, 70, "c0ffee", false, "png", 0, 0, 0, 0}},
+		{"q70,1x2,fit,r90,fv,fh,sc0ffee,png", Options{1, 2, true, 90, true, true, 70, "c0ffee", false, "png", 0, 0, 0, 0, false}},
-		{"r90,fh,sc0ffee,png,q90,1x2,fv,fit", Options{1, 2, true, 90, true, true, 90, "c0ffee", false, "png", 0, 0, 0, 0}},
+		{"r90,fh,sc0ffee,png,q90,1x2,fv,fit", Options{1, 2, true, 90, true, true, 90, "c0ffee", false, "png", 0, 0, 0, 0, false}},
 
 		// all flags, in different orders with crop
-		{"q70,cx100,cw300,1x2,fit,cy200,r90,fv,ch400,fh,sc0ffee,png", Options{1, 2, true, 90, true, true, 70, "c0ffee", false, "png", 100, 200, 300, 400}},
+		{"q70,cx100,cw300,1x2,fit,cy200,r90,fv,ch400,fh,sc0ffee,png", Options{1, 2, true, 90, true, true, 70, "c0ffee", false, "png", 100, 200, 300, 400, false}},
-		{"ch400,r90,cw300,fh,sc0ffee,png,cx100,q90,cy200,1x2,fv,fit", Options{1, 2, true, 90, true, true, 90, "c0ffee", false, "png", 100, 200, 300, 400}},
+		{"ch400,r90,cw300,fh,sc0ffee,png,cx100,q90,cy200,1x2,fv,fit", Options{1, 2, true, 90, true, true, 90, "c0ffee", false, "png", 100, 200, 300, 400, false}},
 
 		// all flags, in different orders with crop & different resizes
-		{"q70,cx100,cw300,x2,fit,cy200,r90,fv,ch400,fh,sc0ffee,png", Options{0, 2, true, 90, true, true, 70, "c0ffee", false, "png", 100, 200, 300, 400}},
+		{"q70,cx100,cw300,x2,fit,cy200,r90,fv,ch400,fh,sc0ffee,png", Options{0, 2, true, 90, true, true, 70, "c0ffee", false, "png", 100, 200, 300, 400, false}},
-		{"ch400,r90,cw300,fh,sc0ffee,png,cx100,q90,cy200,1x,fv,fit", Options{1, 0, true, 90, true, true, 90, "c0ffee", false, "png", 100, 200, 300, 400}},
+		{"ch400,r90,cw300,fh,sc0ffee,png,cx100,q90,cy200,1x,fv,fit", Options{1, 0, true, 90, true, true, 90, "c0ffee", false, "png", 100, 200, 300, 400, false}},
-		{"ch400,r90,cw300,fh,sc0ffee,png,cx100,q90,cy200,cw,fv,fit", Options{0, 0, true, 90, true, true, 90, "c0ffee", false, "png", 100, 200, 0, 400}},
+		{"ch400,r90,cw300,fh,sc0ffee,png,cx100,q90,cy200,cw,fv,fit", Options{0, 0, true, 90, true, true, 90, "c0ffee", false, "png", 100, 200, 0, 400, false}},
-		{"ch400,r90,cw300,fh,sc0ffee,png,cx100,q90,cy200,cw,fv,fit,123x321", Options{123, 321, true, 90, true, true, 90, "c0ffee", false, "png", 100, 200, 0, 400}},
+		{"ch400,r90,cw300,fh,sc0ffee,png,cx100,q90,cy200,cw,fv,fit,123x321", Options{123, 321, true, 90, true, true, 90, "c0ffee", false, "png", 100, 200, 0, 400, false}},
-		{"123x321,ch400,r90,cw300,fh,sc0ffee,png,cx100,q90,cy200,cw,fv,fit", Options{123, 321, true, 90, true, true, 90, "c0ffee", false, "png", 100, 200, 0, 400}},
+		{"123x321,ch400,r90,cw300,fh,sc0ffee,png,cx100,q90,cy200,cw,fv,fit", Options{123, 321, true, 90, true, true, 90, "c0ffee", false, "png", 100, 200, 0, 400, false}},
 	}
 
 	for _, tt := range tests {

transform.go

@@ -22,9 +22,11 @@ import (
 	"image/jpeg"
 	"image/png"
 	"io"
+	"log"
 	"math"
 
 	"github.com/disintegration/imaging"
+	"github.com/muesli/smartcrop"
 	"github.com/rwcarlsen/goexif/exif"
 	"golang.org/x/image/tiff"   // register tiff format
 	_ "golang.org/x/image/webp" // register webp format
@@ -156,7 +158,7 @@ func resizeParams(m image.Image, opt Options) (w, h int, resize bool) {
 
 // cropParams calculates crop rectangle parameters to keep it in image bounds
 func cropParams(m image.Image, opt Options) image.Rectangle {
-	if opt.CropX == 0 && opt.CropY == 0 && opt.CropWidth == 0 && opt.CropHeight == 0 {
+	if !opt.SmartCrop && opt.CropX == 0 && opt.CropY == 0 && opt.CropWidth == 0 && opt.CropHeight == 0 {
 		return m.Bounds()
 	}
 
@@ -164,6 +166,19 @@ func cropParams(m image.Image, opt Options) image.Rectangle {
 	imgW := m.Bounds().Dx()
 	imgH := m.Bounds().Dy()
 
+	if opt.SmartCrop {
+		w := evaluateFloat(opt.Width, imgW)
+		h := evaluateFloat(opt.Height, imgH)
+		log.Printf("smartcrop input: %dx%d", w, h)
+		r, err := smartcrop.SmartCrop(m, w, h)
+		if err != nil {
+			log.Printf("error with smartcrop: %v", err)
+		} else {
+			log.Printf("smartcrop rectangle: %v", r)
+			return r
+		}
+	}
+
 	// top left coordinate of crop
 	x0 := evaluateFloat(math.Abs(opt.CropX), imgW)
 	if opt.CropX < 0 {