Add $image.Process

Which supports all the existing actions: resize, crop, fit, fill.

But it also allows plain format conversions:

```
{{ $img = $img.Process "webp" }}
```

Which will be a simple re-encoding of the source image.

Fixes #11483

resources/image.go

@@ -31,6 +31,7 @@ import (
 
 	color_extractor "github.com/marekm4/color-extractor"
 
+	"github.com/gohugoio/hugo/common/hstrings"
 	"github.com/gohugoio/hugo/common/paths"
 	"github.com/gohugoio/hugo/identity"
 
@@ -198,75 +199,49 @@ func (i *imageResource) cloneWithUpdates(u *transformationUpdate) (baseResource,
 	}, nil
 }
 
+var imageActions = []string{images.ActionResize, images.ActionCrop, images.ActionFit, images.ActionFill}
+
+// Process processes the image with the given spec.
+// The spec can contain an optional action, one of "resize", "crop", "fit" or "fill".
+// This makes this method a more flexible version that covers all of Resize, Crop, Fit and Fill,
+// but it also supports e.g. format conversions without any resize action.
+func (i *imageResource) Process(spec string) (images.ImageResource, error) {
+	var action string
+	options := strings.Fields(spec)
+	for i, p := range options {
+		if hstrings.InSlicEqualFold(imageActions, p) {
+			action = p
+			options = append(options[:i], options[i+1:]...)
+			break
+		}
+	}
+	return i.processActionOptions(action, options)
+}
+
 // Resize resizes the image to the specified width and height using the specified resampling
 // filter and returns the transformed image. If one of width or height is 0, the image aspect
 // ratio is preserved.
 func (i *imageResource) Resize(spec string) (images.ImageResource, error) {
-	conf, err := i.decodeImageConfig("resize", spec)
-	if err != nil {
-		return nil, err
-	}
-
-	return i.doWithImageConfig(conf, func(src image.Image) (image.Image, error) {
-		return i.Proc.ApplyFiltersFromConfig(src, conf)
-	})
+	return i.processActionSpec(images.ActionResize, spec)
 }
 
 // Crop the image to the specified dimensions without resizing using the given anchor point.
 // Space delimited config, e.g. `200x300 TopLeft`.
 func (i *imageResource) Crop(spec string) (images.ImageResource, error) {
-	conf, err := i.decodeImageConfig("crop", spec)
-	if err != nil {
-		return nil, err
-	}
-
-	return i.doWithImageConfig(conf, func(src image.Image) (image.Image, error) {
-		return i.Proc.ApplyFiltersFromConfig(src, conf)
-	})
+	return i.processActionSpec(images.ActionCrop, spec)
 }
 
 // Fit scales down the image using the specified resample filter to fit the specified
 // maximum width and height.
 func (i *imageResource) Fit(spec string) (images.ImageResource, error) {
-	conf, err := i.decodeImageConfig("fit", spec)
-	if err != nil {
-		return nil, err
-	}
-
-	return i.doWithImageConfig(conf, func(src image.Image) (image.Image, error) {
-		return i.Proc.ApplyFiltersFromConfig(src, conf)
-	})
+	return i.processActionSpec(images.ActionFit, spec)
 }
 
 // Fill scales the image to the smallest possible size that will cover the specified dimensions,
 // crops the resized image to the specified dimensions using the given anchor point.
 // Space delimited config, e.g. `200x300 TopLeft`.
 func (i *imageResource) Fill(spec string) (images.ImageResource, error) {
-	conf, err := i.decodeImageConfig("fill", spec)
-	if err != nil {
-		return nil, err
-	}
-
-	img, err := i.doWithImageConfig(conf, func(src image.Image) (image.Image, error) {
-		return i.Proc.ApplyFiltersFromConfig(src, conf)
-	})
-
-	if err != nil {
-		return nil, err
-	}
-
-	if conf.Anchor == 0 && img.Width() == 0 || img.Height() == 0 {
-		// See https://github.com/gohugoio/hugo/issues/7955
-		// Smartcrop fails silently in some rare cases.
-		// Fall back to a center fill.
-		conf.Anchor = gift.CenterAnchor
-		conf.AnchorStr = "center"
-		return i.doWithImageConfig(conf, func(src image.Image) (image.Image, error) {
-			return i.Proc.ApplyFiltersFromConfig(src, conf)
-		})
-	}
-
-	return img, err
+	return i.processActionSpec(images.ActionFill, spec)
 }
 
 func (i *imageResource) Filter(filters ...any) (images.ImageResource, error) {
@@ -286,6 +261,39 @@ func (i *imageResource) Filter(filters ...any) (images.ImageResource, error) {
 	})
 }
 
+func (i *imageResource) processActionSpec(action, spec string) (images.ImageResource, error) {
+	return i.processActionOptions(action, strings.Fields(spec))
+}
+
+func (i *imageResource) processActionOptions(action string, options []string) (images.ImageResource, error) {
+	conf, err := images.DecodeImageConfig(action, options, i.Proc.Cfg, i.Format)
+	if err != nil {
+		return nil, err
+	}
+
+	img, err := i.doWithImageConfig(conf, func(src image.Image) (image.Image, error) {
+		return i.Proc.ApplyFiltersFromConfig(src, conf)
+	})
+	if err != nil {
+		return nil, err
+	}
+
+	if action == images.ActionFill {
+		if conf.Anchor == 0 && img.Width() == 0 || img.Height() == 0 {
+			// See https://github.com/gohugoio/hugo/issues/7955
+			// Smartcrop fails silently in some rare cases.
+			// Fall back to a center fill.
+			conf.Anchor = gift.CenterAnchor
+			conf.AnchorStr = "center"
+			return i.doWithImageConfig(conf, func(src image.Image) (image.Image, error) {
+				return i.Proc.ApplyFiltersFromConfig(src, conf)
+			})
+		}
+	}
+
+	return img, nil
+}
+
 // Serialize image processing. The imaging library spins up its own set of Go routines,
 // so there is not much to gain from adding more load to the mix. That
 // can even have negative effect in low resource scenarios.
@@ -362,7 +370,8 @@ 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, i.Format)
+	options := strings.Fields(spec)
+	conf, err := images.DecodeImageConfig(action, options, i.Proc.Cfg, i.Format)
 	if err != nil {
 		return conf, err
 	}