resources/images: Allow to set background fill colour

Closes #6298

15 files changed, 356 insertions, 45 deletions

diff --git a/docs/content/en/content-management/image-processing/index.md b/docs/content/en/content-management/image-processing/index.md
index b83a6c103..f03c5bee6 100644
--- a/docs/content/en/content-management/image-processing/index.md
+++ b/docs/content/en/content-management/image-processing/index.md
@@ -2,7 +2,6 @@
 title: "Image Processing"
 description: "Image Page resources can be resized and cropped."
 date: 2018-01-24T13:10:00-05:00
-lastmod: 2018-01-26T15:59:07-05:00
 linktitle: "Image Processing"
 categories: ["content management"]
 keywords: [bundle,content,resources,images]
@@ -72,31 +71,42 @@ Image operations in Hugo currently **do not preserve EXIF data** as this is not
 
 In addition to the dimensions (e.g. `600x400`), Hugo supports a set of additional image options.
 
+### Background Color
 
-JPEG Quality
-: Only relevant for JPEG images, values 1 to 100 inclusive, higher is better. Default is 75.
+The background color to fill into the transparency layer. This is mostly useful when converting to a format that does not support transparency, e.g. `JPEG`.
+
+You can set the background color to use with a 3 or 6 digit hex code starting with `#`.
+
+```go
+{{ $image.Resize "600x jpg #b31280" }}
+```
+
+For color codes, see https://www.google.com/search?q=color+picker
+
+### JPEG Quality
+Only relevant for JPEG images, values 1 to 100 inclusive, higher is better. Default is 75.
 
 ```go
 {{ $image.Resize "600x q50" }}
 ```
 
-Rotate
-: Rotates an image by the given angle counter-clockwise. The rotation will be performed first to get the dimensions correct. The main use of this is to be able to manually correct for [EXIF orientation](https://github.com/golang/go/issues/4341) of JPEG images.
+### Rotate
+Rotates an image by the given angle counter-clockwise. The rotation will be performed first to get the dimensions correct. The main use of this is to be able to manually correct for [EXIF orientation](https://github.com/golang/go/issues/4341) of JPEG images.
 
 ```go
 {{ $image.Resize "600x r90" }}
 ```
 
-Anchor
-: Only relevant for the `Fill` method. This is useful for thumbnail generation where the main motive is located in, say, the left corner. 
+###  Anchor
+Only relevant for the `Fill` method. This is useful for thumbnail generation where the main motive is located in, say, the left corner. 
 Valid are `Center`, `TopLeft`, `Top`, `TopRight`, `Left`, `Right`, `BottomLeft`, `Bottom`, `BottomRight`.
 
 ```go
 {{ $image.Fill "300x200 BottomLeft" }}
 ```
 
-Resample Filter
-: Filter used in resizing. Default is `Box`, a simple and fast resampling filter appropriate for downscaling. 
+### Resample Filter
+Filter used in resizing. Default is `Box`, a simple and fast resampling filter appropriate for downscaling. 
 
 Examples are: `Box`, `NearestNeighbor`, `Linear`, `Gaussian`.
 
@@ -106,6 +116,16 @@ See https://github.com/disintegration/imaging for more. If you want to trade qua
 {{ $image.Resize "600x400 Gaussian" }}
 ```
 
+### Target Format
+
+By default the images is encoded in the source format, but you can set the target format as an option.
+
+Valid values are `jpg`, `png`, `tif`, `bmp`, and `gif`.
+
+```go
+{{ $image.Resize "600x jpg" }}
+```
+
 ## Image Processing Examples
 
 _The photo of the sunset used in the examples below is Copyright [Bjørn Erik Pedersen](https://commons.wikimedia.org/wiki/User:Bep) (Creative Commons Attribution-Share Alike 4.0 International license)_
@@ -160,6 +180,13 @@ quality = 75
 # Valid values are Smart, Center, TopLeft, Top, TopRight, Left, Right, BottomLeft, Bottom, BottomRight
 anchor = "smart"
 
+# Default background color. 
+# Hugo will preserve transparency for target formats that supports it,
+# but will fall back to this color for JPEG.
+# Expects a standard HEX color string with 3 or 6 digits.
+# See https://www.google.com/search?q=color+picker
+bgColor = "#ffffff"
+
 ```
 
 All of the above settings can also be set per image procecssing.
diff --git a/hugolib/image_test.go b/hugolib/image_test.go
index a13338afc..d0bff75a2 100644
--- a/hugolib/image_test.go
+++ b/hugolib/image_test.go
@@ -205,10 +205,11 @@ SUNSET2: {{ $resized2.RelPermalink }}/{{ $resized2.Width }}/Lat: {{ $resized2.Ex
 
 	// Check the file cache
 	b.AssertImage(200, 200, "resources/_gen/images/bundle/sunset_hu59e56ffff1bc1d8d122b1403d34e039f_90587_200x200_resize_q75_box.jpg")
-	b.AssertFileContent("resources/_gen/images/bundle/sunset_17701188623491591036.json",
+
+	b.AssertFileContent("resources/_gen/images/bundle/sunset_7645215769587362592.json",
 		"DateTimeDigitized|time.Time", "PENTAX")
 	b.AssertImage(123, 234, "resources/_gen/images/sunset_hu59e56ffff1bc1d8d122b1403d34e039f_90587_123x234_resize_q75_box.jpg")
-	b.AssertFileContent("resources/_gen/images/sunset_17701188623491591036.json",
+	b.AssertFileContent("resources/_gen/images/sunset_7645215769587362592.json",
 		"DateTimeDigitized|time.Time", "PENTAX")
 
 	// TODO(bep) add this as a default assertion after Build()?
diff --git a/resources/image.go b/resources/image.go
index bb9c987a5..1991e65f5 100644
--- a/resources/image.go
+++ b/resources/image.go
@@ -17,6 +17,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"image"
+	"image/color"
 	"image/draw"
 	_ "image/gif"
 	_ "image/png"
@@ -254,10 +255,32 @@ func (i *imageResource) doWithImageConfig(conf images.ImageConfig, f func(src im
 			return nil, nil, &os.PathError{Op: errOp, Path: errPath, Err: err}
 		}
 
+		hasAlpha := !images.IsOpaque(converted)
+		shouldFill := conf.BgColor != nil && hasAlpha
+		shouldFill = shouldFill || (!conf.TargetFormat.SupportsTransparency() && hasAlpha)
+		var bgColor color.Color
+
+		if shouldFill {
+			bgColor = conf.BgColor
+			if bgColor == nil {
+				bgColor = i.Proc.Cfg.BgColor
+			}
+			tmp := image.NewRGBA(converted.Bounds())
+			draw.Draw(tmp, tmp.Bounds(), image.NewUniform(bgColor), image.Point{}, draw.Src)
+			draw.Draw(tmp, tmp.Bounds(), converted, converted.Bounds().Min, draw.Over)
+			converted = tmp
+		}
+
 		if conf.TargetFormat == images.PNG {
 			// Apply the colour palette from the source
 			if paletted, ok := src.(*image.Paletted); ok {
-				tmp := image.NewPaletted(converted.Bounds(), paletted.Palette)
+				palette := paletted.Palette
+				if bgColor != nil && len(palette) < 256 {
+					palette = images.AddColorToPalette(bgColor, palette)
+				} else if bgColor != nil {
+					images.ReplaceColorInPalette(bgColor, palette)
+				}
+				tmp := image.NewPaletted(converted.Bounds(), palette)
 				draw.FloydSteinberg.Draw(tmp, tmp.Bounds(), converted, converted.Bounds().Min)
 				converted = tmp
 			}
@@ -273,7 +296,7 @@ func (i *imageResource) doWithImageConfig(conf images.ImageConfig, f func(src im
 }
 
 func (i *imageResource) decodeImageConfig(action, spec string) (images.ImageConfig, error) {
-	conf, err := images.DecodeImageConfig(action, spec, i.Proc.Cfg)
+	conf, err := images.DecodeImageConfig(action, spec, i.Proc.Cfg.Cfg)
 	if err != nil {
 		return conf, err
 	}
@@ -285,7 +308,14 @@ func (i *imageResource) decodeImageConfig(action, spec string) (images.ImageConf
 
 	if conf.Quality <= 0 && conf.TargetFormat.RequiresDefaultQuality() {
 		// We need a quality setting for all JPEGs
-		conf.Quality = i.Proc.Cfg.Quality
+		conf.Quality = i.Proc.Cfg.Cfg.Quality
+	}
+
+	if conf.BgColor == nil && conf.TargetFormat != i.Format {
+		if i.Format.SupportsTransparency() && !conf.TargetFormat.SupportsTransparency() {
+			conf.BgColor = i.Proc.Cfg.BgColor
+			conf.BgColorStr = i.Proc.Cfg.Cfg.BgColor
+		}
 	}
 
 	return conf, nil
@@ -325,7 +355,7 @@ func (i *imageResource) setBasePath(conf images.ImageConfig) {
 func (i *imageResource) getImageMetaCacheTargetPath() string {
 	const imageMetaVersionNumber = 1 // Increment to invalidate the meta cache
 
-	cfg := i.getSpec().imaging.Cfg
+	cfg := i.getSpec().imaging.Cfg.Cfg
 	df := i.getResourcePaths().relTargetDirFile
 	if fi := i.getFileInfo(); fi != nil {
 		df.dir = filepath.Dir(fi.Meta().Path())
diff --git a/resources/image_test.go b/resources/image_test.go
index 4b88b7aa1..89e686ed1 100644
--- a/resources/image_test.go
+++ b/resources/image_test.go
@@ -22,7 +22,6 @@ import (
 	"os"
 	"path"
 	"path/filepath"
-	"regexp"
 	"runtime"
 	"strconv"
 	"sync"
@@ -540,6 +539,18 @@ func TestImageOperationsGolden(t *testing.T) {
 		fmt.Println(workDir)
 	}
 
+	// Test PNGs with alpha channel.
+	for _, img := range []string{"gopher-hero8.png", "gradient-circle.png"} {
+		orig := fetchImageForSpec(spec, c, img)
+		for _, resizeSpec := range []string{"200x #e3e615", "200x jpg #e3e615"} {
+			resized, err := orig.Resize(resizeSpec)
+			c.Assert(err, qt.IsNil)
+			rel := resized.RelPermalink()
+			c.Log("resize", rel)
+			c.Assert(rel, qt.Not(qt.Equals), "")
+		}
+	}
+
 	for _, img := range testImages {
 
 		orig := fetchImageForSpec(spec, c, img)
@@ -618,9 +629,6 @@ func TestImageOperationsGolden(t *testing.T) {
 	c.Assert(len(dirinfos1), qt.Equals, len(dirinfos2))
 
 	for i, fi1 := range dirinfos1 {
-		if regexp.MustCompile("gauss").MatchString(fi1.Name()) {
-			continue
-		}
 		fi2 := dirinfos2[i]
 		c.Assert(fi1.Name(), qt.Equals, fi2.Name())
 
diff --git a/resources/images/color.go b/resources/images/color.go
new file mode 100644
index 000000000..b17173e26
--- /dev/null
+++ b/resources/images/color.go
@@ -0,0 +1,85 @@
+// Copyright 2019 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package images
+
+import (
+	"encoding/hex"
+	"image/color"
+	"strings"
+
+	"github.com/pkg/errors"
+)
+
+// AddColorToPalette adds c as the first color in p if not already there.
+// Note that it does no additional checks, so callers must make sure
+// that the palette is valid for the relevant format.
+func AddColorToPalette(c color.Color, p color.Palette) color.Palette {
+	var found bool
+	for _, cc := range p {
+		if c == cc {
+			found = true
+			break
+		}
+	}
+
+	if !found {
+		p = append(color.Palette{c}, p...)
+	}
+
+	return p
+}
+
+// ReplaceColorInPalette will replace the color in palette p closest to c in Euclidean
+// R,G,B,A space with c.
+func ReplaceColorInPalette(c color.Color, p color.Palette) {
+	p[p.Index(c)] = c
+}
+
+func hexStringToColor(s string) (color.Color, error) {
+	s = strings.TrimPrefix(s, "#")
+
+	if len(s) != 3 && len(s) != 6 {
+		return nil, errors.Errorf("invalid color code: %q", s)
+	}
+
+	s = strings.ToLower(s)
+
+	if len(s) == 3 {
+		var v string
+		for _, r := range s {
+			v += string(r) + string(r)
+		}
+		s = v
+	}
+
+	// Standard colors.
+	if s == "ffffff" {
+		return color.White, nil
+	}
+
+	if s == "000000" {
+		return color.Black, nil
+	}
+
+	// Set Alfa to white.
+	s += "ff"
+
+	b, err := hex.DecodeString(s)
+	if err != nil {
+		return nil, err
+	}
+
+	return color.RGBA{b[0], b[1], b[2], b[3]}, nil
+
+}
diff --git a/resources/images/color_test.go b/resources/images/color_test.go
new file mode 100644
index 000000000..3ef9f76cc
--- /dev/null
+++ b/resources/images/color_test.go
@@ -0,0 +1,90 @@
+// Copyright 2019 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package images
+
+import (
+	"image/color"
+	"testing"
+
+	qt "github.com/frankban/quicktest"
+)
+
+func TestHexStringToColor(t *testing.T) {
+	c := qt.New(t)
+
+	for _, test := range []struct {
+		arg    string
+		expect interface{}
+	}{
+		{"f", false},
+		{"#f", false},
+		{"#fffffff", false},
+		{"fffffff", false},
+		{"#fff", color.White},
+		{"fff", color.White},
+		{"FFF", color.White},
+		{"FfF", color.White},
+		{"#ffffff", color.White},
+		{"ffffff", color.White},
+		{"#000", color.Black},
+		{"#4287f5", color.RGBA{R: 0x42, G: 0x87, B: 0xf5, A: 0xff}},
+		{"777", color.RGBA{R: 0x77, G: 0x77, B: 0x77, A: 0xff}},
+	} {
+
+		test := test
+		c.Run(test.arg, func(c *qt.C) {
+			c.Parallel()
+
+			result, err := hexStringToColor(test.arg)
+
+			if b, ok := test.expect.(bool); ok && !b {
+				c.Assert(err, qt.Not(qt.IsNil))
+				return
+			}
+
+			c.Assert(err, qt.IsNil)
+			c.Assert(result, qt.DeepEquals, test.expect)
+		})
+
+	}
+}
+
+func TestAddColorToPalette(t *testing.T) {
+	c := qt.New(t)
+
+	palette := color.Palette{color.White, color.Black}
+
+	c.Assert(AddColorToPalette(color.White, palette), qt.HasLen, 2)
+
+	blue1, _ := hexStringToColor("34c3eb")
+	blue2, _ := hexStringToColor("34c3eb")
+	white, _ := hexStringToColor("fff")
+
+	c.Assert(AddColorToPalette(white, palette), qt.HasLen, 2)
+	c.Assert(AddColorToPalette(blue1, palette), qt.HasLen, 3)
+	c.Assert(AddColorToPalette(blue2, palette), qt.HasLen, 3)
+
+}
+
+func TestReplaceColorInPalette(t *testing.T) {
+	c := qt.New(t)
+
+	palette := color.Palette{color.White, color.Black}
+	offWhite, _ := hexStringToColor("fcfcfc")
+
+	ReplaceColorInPalette(offWhite, palette)
+
+	c.Assert(palette, qt.HasLen, 2)
+	c.Assert(palette[0], qt.Equals, offWhite)
+}
diff --git a/resources/images/config.go b/resources/images/config.go
index 6bc701bfe..7b2ade29f 100644
--- a/resources/images/config.go
+++ b/resources/images/config.go
@@ -16,6 +16,7 @@ package images
 import (
 	"errors"
 	"fmt"
+	"image/color"
 	"strconv"
 	"strings"
 
@@ -27,6 +28,7 @@ import (
 const (
 	defaultJPEGQuality    = 75
 	defaultResampleFilter = "box"
+	defaultBgColor        = "ffffff"
 )
 
 var (
@@ -87,16 +89,28 @@ func ImageFormatFromExt(ext string) (Format, bool) {
 	return f, found
 }
 
-func DecodeConfig(m map[string]interface{}) (Imaging, error) {
+func DecodeConfig(m map[string]interface{}) (ImagingConfig, error) {
 	var i Imaging
+	var ic ImagingConfig
 	if err := mapstructure.WeakDecode(m, &i); err != nil {
-		return i, err
+		return ic, err
 	}
 
 	if i.Quality == 0 {
 		i.Quality = defaultJPEGQuality
 	} else if i.Quality < 0 || i.Quality > 100 {
-		return i, errors.New("JPEG quality must be a number between 1 and 100")
+		return ic, errors.New("JPEG quality must be a number between 1 and 100")
+	}
+
+	if i.BgColor != "" {
+		i.BgColor = strings.TrimPrefix(i.BgColor, "#")
+	} else {
+		i.BgColor = defaultBgColor
+	}
+	var err error
+	ic.BgColor, err = hexStringToColor(i.BgColor)
+	if err != nil {
+		return ic, err
 	}
 
 	if i.Anchor == "" || strings.EqualFold(i.Anchor, smartCropIdentifier) {
@@ -104,7 +118,7 @@ func DecodeConfig(m map[string]interface{}) (Imaging, error) {
 	} else {
 		i.Anchor = strings.ToLower(i.Anchor)
 		if _, found := anchorPositions[i.Anchor]; !found {
-			return i, errors.New("invalid anchor value in imaging config")
+			return ic, errors.New("invalid anchor value in imaging config")
 		}
 	}
 
@@ -114,7 +128,7 @@ func DecodeConfig(m map[string]interface{}) (Imaging, error) {
 		filter := strings.ToLower(i.ResampleFilter)
 		_, found := imageFilters[filter]
 		if !found {
-			return i, fmt.Errorf("%q is not a valid resample filter", filter)
+			return ic, fmt.Errorf("%q is not a valid resample filter", filter)
 		}
 		i.ResampleFilter = filter
 	}
@@ -124,7 +138,9 @@ func DecodeConfig(m map[string]interface{}) (Imaging, error) {
 		i.Exif.ExcludeFields = "GPS|Exif|Exposure[M|P|B]|Contrast|Resolution|Sharp|JPEG|Metering|Sensing|Saturation|ColorSpace|Flash|WhiteBalance"
 	}
 
-	return i, nil
+	ic.Cfg = i
+
+	return ic, nil
 }
 
 func DecodeImageConfig(action, config string, defaults Imaging) (ImageConfig, error) {
@@ -151,6 +167,12 @@ func DecodeImageConfig(action, config string, defaults Imaging) (ImageConfig, er
 		} else if filter, ok := imageFilters[part]; ok {
 			c.Filter = filter
 			c.FilterStr = part
+		} else if part[0] == '#' {
+			c.BgColorStr = part[1:]
+			c.BgColor, err = hexStringToColor(c.BgColorStr)
+			if err != nil {
+				return c, err
+			}
 		} else if part[0] == 'q' {
 			c.Quality, err = strconv.Atoi(part[1:])
 			if err != nil {
@@ -230,6 +252,14 @@ type ImageConfig struct {
 	// The rotation will be performed first.
 	Rotate int
 
+	// Used to fill any transparency.
+	// When set in site config, it's used when converting to a format that does
+	// not support transparency.
+	// When set per image operation, it's used even for formats that does support
+	// transparency.
+	BgColor    color.Color
+	BgColorStr string
+
 	Width  int
 	Height int
 
@@ -255,6 +285,10 @@ func (i ImageConfig) GetKey(format Format) string {
 	if i.Rotate != 0 {
 		k += "_r" + strconv.Itoa(i.Rotate)
 	}
+	if i.BgColorStr != "" {
+		k += "_bg" + i.BgColorStr
+	}
+
 	anchor := i.AnchorStr
 	if anchor == smartCropIdentifier {
 		anchor = anchor + strconv.Itoa(smartCropVersionNumber)
@@ -277,6 +311,13 @@ func (i ImageConfig) GetKey(format Format) string {
 	return k
 }
 
+type ImagingConfig struct {
+	BgColor color.Color
+
+	// Config as provided by the user.
+	Cfg Imaging
+}
+
 // Imaging contains default image processing configuration. This will be fetched
 // from site (or language) config.
 type Imaging struct {
@@ -289,6 +330,9 @@ type Imaging struct {
 	// The anchor to use in Fill. Default is "smart", i.e. Smart Crop.
 	Anchor string
 
+	// Default color used in fill operations (e.g. "fff" for white).
+	BgColor string
+
 	Exif ExifConfig
 }
 
diff --git a/resources/images/config_test.go b/resources/images/config_test.go
index 46b0c9858..f60cce9ef 100644
--- a/resources/images/config_test.go
+++ b/resources/images/config_test.go
@@ -29,17 +29,19 @@ func TestDecodeConfig(t *testing.T) {
 		"anchor":         "topLeft",
 	}
 
-	imaging, err := DecodeConfig(m)
+	imagingConfig, err := DecodeConfig(m)
 
 	c.Assert(err, qt.IsNil)
+	imaging := imagingConfig.Cfg
 	c.Assert(imaging.Quality, qt.Equals, 42)
 	c.Assert(imaging.ResampleFilter, qt.Equals, "nearestneighbor")
 	c.Assert(imaging.Anchor, qt.Equals, "topleft")
 
 	m = map[string]interface{}{}
 
-	imaging, err = DecodeConfig(m)
+	imagingConfig, err = DecodeConfig(m)
 	c.Assert(err, qt.IsNil)
+	imaging = imagingConfig.Cfg
 	c.Assert(imaging.Quality, qt.Equals, defaultJPEGQuality)
 	c.Assert(imaging.ResampleFilter, qt.Equals, "box")
 	c.Assert(imaging.Anchor, qt.Equals, "smart")
@@ -59,18 +61,20 @@ func TestDecodeConfig(t *testing.T) {
 	})
 	c.Assert(err, qt.Not(qt.IsNil))
 
-	imaging, err = DecodeConfig(map[string]interface{}{
+	imagingConfig, err = DecodeConfig(map[string]interface{}{
 		"anchor": "Smart",
 	})
+	imaging = imagingConfig.Cfg
 	c.Assert(err, qt.IsNil)
 	c.Assert(imaging.Anchor, qt.Equals, "smart")
 
-	imaging, err = DecodeConfig(map[string]interface{}{
+	imagingConfig, err = DecodeConfig(map[string]interface{}{
 		"exif": map[string]interface{}{
 			"disableLatLong": true,
 		},
 	})
 	c.Assert(err, qt.IsNil)
+	imaging = imagingConfig.Cfg
 	c.Assert(imaging.Exif.DisableLatLong, qt.Equals, true)
 	c.Assert(imaging.Exif.ExcludeFields, qt.Equals, "GPS|Exif|Exposure[M|P|B]|Contrast|Resolution|Sharp|JPEG|Metering|Sensing|Saturation|ColorSpace|Flash|WhiteBalance")
 
@@ -81,11 +85,12 @@ func TestDecodeImageConfig(t *testing.T) {
 		in     string
 		expect interface{}
 	}{
-		{"300x400", newImageConfig(300, 400, 0, 0, "", "")},
-		{"100x200 bottomRight", newImageConfig(100, 200, 0, 0, "", "BottomRight")},
-		{"10x20 topleft Lanczos", newImageConfig(10, 20, 0, 0, "Lanczos", "topleft")},
-		{"linear left 10x r180", newImageConfig(10, 0, 0, 180, "linear", "left")},
-		{"x20 riGht Cosine q95", newImageConfig(0, 20, 95, 0, "cosine", "right")},
+		{"300x400", newImageConfig(300, 400, 0, 0, "", "", "")},
+		{"300x400 #fff", newImageConfig(300, 400, 0, 0, "", "", "fff")},
+		{"100x200 bottomRight", newImageConfig(100, 200, 0, 0, "", "BottomRight", "")},
+		{"10x20 topleft Lanczos", newImageConfig(10, 20, 0, 0, "Lanczos", "topleft", "")},
+		{"linear left 10x r180", newImageConfig(10, 0, 0, 180, "linear", "left", "")},
+		{"x20 riGht Cosine q95", newImageConfig(0, 20, 95, 0, "cosine", "right", "")},
 
 		{"", false},
 		{"foo", false},
@@ -107,13 +112,15 @@ func TestDecodeImageConfig(t *testing.T) {
 	}
 }
 
-func newImageConfig(width, height, quality, rotate int, filter, anchor string) ImageConfig {
+func newImageConfig(width, height, quality, rotate int, filter, anchor, bgColor string) ImageConfig {
 	var c ImageConfig
 	c.Action = "resize"
 	c.Width = width
 	c.Height = height
 	c.Quality = quality
 	c.Rotate = rotate
+	c.BgColorStr = bgColor
+	c.BgColor, _ = hexStringToColor(bgColor)
 
 	if filter != "" {
 		filter = strings.ToLower(filter)
diff --git a/resources/images/image.go b/resources/images/image.go
index bd7500c28..bac05ab70 100644
--- a/resources/images/image.go
+++ b/resources/images/image.go
@@ -51,11 +51,8 @@ func NewImage(f Format, proc *ImageProcessor, img image.Image, s Spec) *Image {
 
 type Image struct {
 	Format Format
-
-	Proc *ImageProcessor
-
-	Spec Spec
-
+	Proc   *ImageProcessor
+	Spec   Spec
 	*imageConfig
 }
 
@@ -158,8 +155,8 @@ func (i *Image) initConfig() error {
 	return nil
 }
 
-func NewImageProcessor(cfg Imaging) (*ImageProcessor, error) {
-	e := cfg.Exif
+func NewImageProcessor(cfg ImagingConfig) (*ImageProcessor, error) {
+	e := cfg.Cfg.Exif
 	exifDecoder, err := exif.NewDecoder(
 		exif.WithDateDisabled(e.DisableDate),
 		exif.WithLatLongDisabled(e.DisableLatLong),
@@ -179,7 +176,7 @@ func NewImageProcessor(cfg Imaging) (*ImageProcessor, error) {
 }
 
 type ImageProcessor struct {
-	Cfg         Imaging
+	Cfg         ImagingConfig
 	exifDecoder *exif.Decoder
 }
 
@@ -218,7 +215,12 @@ func (p *ImageProcessor) ApplyFiltersFromConfig(src image.Image, conf ImageConfi
 		return nil, errors.Errorf("unsupported action: %q", conf.Action)
 	}
 
-	return p.Filter(src, filters...)
+	img, err := p.Filter(src, filters...)
+	if err != nil {
+		return nil, err
+	}
+
+	return img, nil
 }
 
 func (p *ImageProcessor) Filter(src image.Image, filters ...gift.Filter) (image.Image, error) {
@@ -231,7 +233,7 @@ func (p *ImageProcessor) Filter(src image.Image, filters ...gift.Filter) (image.
 func (p *ImageProcessor) GetDefaultImageConfig(action string) ImageConfig {
 	return ImageConfig{
 		Action:  action,
-		Quality: p.Cfg.Quality,
+		Quality: p.Cfg.Cfg.Quality,
 	}
 }
 
@@ -256,6 +258,11 @@ func (f Format) RequiresDefaultQuality() bool {
 	return f == JPEG
 }
 
+// SupportsTransparency reports whether it supports transparency in any form.
+func (f Format) SupportsTransparency() bool {
+	return f != JPEG
+}
+
 // DefaultExtension returns the default file extension of this format, starting with a dot.
 // For example: .jpg for JPEG
 func (f Format) DefaultExtension() string {
@@ -307,3 +314,15 @@ func ToFilters(in interface{}) []gift.Filter {
 		panic(fmt.Sprintf("%T is not an image filter", in))
 	}
 }
+
+// IsOpaque returns false if the image has alpha channel and there is at least 1
+// pixel that is not (fully) opaque.
+func IsOpaque(img image.Image) bool {
+	if oim, ok := img.(interface {
+		Opaque() bool
+	}); ok {
+		return oim.Opaque()
+	}
+
+	return false
+}
diff --git a/resources/testdata/golden/gopher-hero8_huaa0cd7d2cfc14ff32a57f171896f2285_13327_200x0_resize_bge3e615_box_2.png b/resources/testdata/golden/gopher-hero8_huaa0cd7d2cfc14ff32a57f171896f2285_13327_200x0_resize_bge3e615_box_2.png
new file mode 100644
index 000000000..830ee906b
--- /dev/null
+++ b/resources/testdata/golden/gopher-hero8_huaa0cd7d2cfc14ff32a57f171896f2285_13327_200x0_resize_bge3e615_box_2.png
diff --git a/resources/testdata/golden/gopher-hero8_huaa0cd7d2cfc14ff32a57f171896f2285_13327_200x0_resize_q75_bge3e615_box_2.jpg b/resources/testdata/golden/gopher-hero8_huaa0cd7d2cfc14ff32a57f171896f2285_13327_200x0_resize_q75_bge3e615_box_2.jpg
new file mode 100644
index 000000000..4ae6f5173
--- /dev/null
+++ b/resources/testdata/golden/gopher-hero8_huaa0cd7d2cfc14ff32a57f171896f2285_13327_200x0_resize_q75_bge3e615_box_2.jpg
diff --git a/resources/testdata/golden/gradient-circle_huf3d35257a40a8d6f525263a856c5ecfd_20069_200x0_resize_bge3e615_box_2.png b/resources/testdata/golden/gradient-circle_huf3d35257a40a8d6f525263a856c5ecfd_20069_200x0_resize_bge3e615_box_2.png
new file mode 100644
index 000000000..3c861e922
--- /dev/null
+++ b/resources/testdata/golden/gradient-circle_huf3d35257a40a8d6f525263a856c5ecfd_20069_200x0_resize_bge3e615_box_2.png
diff --git a/resources/testdata/golden/gradient-circle_huf3d35257a40a8d6f525263a856c5ecfd_20069_200x0_resize_q75_bge3e615_box_2.jpg b/resources/testdata/golden/gradient-circle_huf3d35257a40a8d6f525263a856c5ecfd_20069_200x0_resize_q75_bge3e615_box_2.jpg
new file mode 100644
index 000000000..beb80bb12
--- /dev/null
+++ b/resources/testdata/golden/gradient-circle_huf3d35257a40a8d6f525263a856c5ecfd_20069_200x0_resize_q75_bge3e615_box_2.jpg
diff --git a/resources/testdata/gopher-hero8.png b/resources/testdata/gopher-hero8.png
new file mode 100644
index 000000000..08ae570d2
--- /dev/null
+++ b/resources/testdata/gopher-hero8.png
diff --git a/resources/testdata/gradient-circle.png b/resources/testdata/gradient-circle.png
new file mode 100644
index 000000000..a4ace53a1
--- /dev/null
+++ b/resources/testdata/gradient-circle.png