hugo/resources/images/filters.go

// 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 provides template functions for manipulating images.
package images

import (
	"github.com/disintegration/gift"
	"github.com/spf13/cast"
)

// Increment for re-generation of images using these filters.
const filterAPIVersion = 0

type Filters struct {
}

// Brightness creates a filter that changes the brightness of an image.
// The percentage parameter must be in range (-100, 100).
func (*Filters) Brightness(percentage interface{}) gift.Filter {
	return filter{
		Options: newFilterOpts(percentage),
		Filter:  gift.Brightness(cast.ToFloat32(percentage)),
	}
}

// ColorBalance creates a filter that changes the color balance of an image.
// The percentage parameters for each color channel (red, green, blue) must be in range (-100, 500).
func (*Filters) ColorBalance(percentageRed, percentageGreen, percentageBlue interface{}) gift.Filter {
	return filter{
		Options: newFilterOpts(percentageRed, percentageGreen, percentageBlue),
		Filter:  gift.ColorBalance(cast.ToFloat32(percentageRed), cast.ToFloat32(percentageGreen), cast.ToFloat32(percentageBlue)),
	}
}

// Colorize creates a filter that produces a colorized version of an image.
// The hue parameter is the angle on the color wheel, typically in range (0, 360).
// The saturation parameter must be in range (0, 100).
// The percentage parameter specifies the strength of the effect, it must be in range (0, 100).
func (*Filters) Colorize(hue, saturation, percentage interface{}) gift.Filter {
	return filter{
		Options: newFilterOpts(hue, saturation, percentage),
		Filter:  gift.Colorize(cast.ToFloat32(hue), cast.ToFloat32(saturation), cast.ToFloat32(percentage)),
	}
}

// Contrast creates a filter that changes the contrast of an image.
// The percentage parameter must be in range (-100, 100).
func (*Filters) Contrast(percentage interface{}) gift.Filter {
	return filter{
		Options: newFilterOpts(percentage),
		Filter:  gift.Contrast(cast.ToFloat32(percentage)),
	}
}

// Gamma creates a filter that performs a gamma correction on an image.
// The gamma parameter must be positive. Gamma = 1 gives the original image.
// Gamma less than 1 darkens the image and gamma greater than 1 lightens it.
func (*Filters) Gamma(gamma interface{}) gift.Filter {
	return filter{
		Options: newFilterOpts(gamma),
		Filter:  gift.Gamma(cast.ToFloat32(gamma)),
	}
}

// GaussianBlur creates a filter that applies a gaussian blur to an image.
func (*Filters) GaussianBlur(sigma interface{}) gift.Filter {
	return filter{
		Options: newFilterOpts(sigma),
		Filter:  gift.GaussianBlur(cast.ToFloat32(sigma)),
	}
}

// Grayscale creates a filter that produces a grayscale version of an image.
func (*Filters) Grayscale() gift.Filter {
	return filter{
		Filter: gift.Grayscale(),
	}
}

// Hue creates a filter that rotates the hue of an image.
// The hue angle shift is typically in range -180 to 180.
func (*Filters) Hue(shift interface{}) gift.Filter {
	return filter{
		Options: newFilterOpts(shift),
		Filter:  gift.Hue(cast.ToFloat32(shift)),
	}
}

// Invert creates a filter that negates the colors of an image.
func (*Filters) Invert() gift.Filter {
	return filter{
		Filter: gift.Invert(),
	}
}

// Pixelate creates a filter that applies a pixelation effect to an image.
func (*Filters) Pixelate(size interface{}) gift.Filter {
	return filter{
		Options: newFilterOpts(size),
		Filter:  gift.Pixelate(cast.ToInt(size)),
	}
}

// Saturation creates a filter that changes the saturation of an image.
func (*Filters) Saturation(percentage interface{}) gift.Filter {
	return filter{
		Options: newFilterOpts(percentage),
		Filter:  gift.Saturation(cast.ToFloat32(percentage)),
	}
}

// Sepia creates a filter that produces a sepia-toned version of an image.
func (*Filters) Sepia(percentage interface{}) gift.Filter {
	return filter{
		Options: newFilterOpts(percentage),
		Filter:  gift.Sepia(cast.ToFloat32(percentage)),
	}
}

// Sigmoid creates a filter that changes the contrast of an image using a sigmoidal function and returns the adjusted image.
// It's a non-linear contrast change useful for photo adjustments as it preserves highlight and shadow detail.
func (*Filters) Sigmoid(midpoint, factor interface{}) gift.Filter {
	return filter{
		Options: newFilterOpts(midpoint, factor),
		Filter:  gift.Sigmoid(cast.ToFloat32(midpoint), cast.ToFloat32(factor)),
	}
}

// UnsharpMask creates a filter that sharpens an image.
// The sigma parameter is used in a gaussian function and affects the radius of effect.
// Sigma must be positive. Sharpen radius roughly equals 3 * sigma.
// The amount parameter controls how much darker and how much lighter the edge borders become. Typically between 0.5 and 1.5.
// The threshold parameter controls the minimum brightness change that will be sharpened. Typically between 0 and 0.05.
func (*Filters) UnsharpMask(sigma, amount, threshold interface{}) gift.Filter {
	return filter{
		Options: newFilterOpts(sigma, amount, threshold),
		Filter:  gift.UnsharpMask(cast.ToFloat32(sigma), cast.ToFloat32(amount), cast.ToFloat32(threshold)),
	}
}

type filter struct {
	Options filterOpts
	gift.Filter
}

// For cache-busting.
type filterOpts struct {
	Version int
	Vals    interface{}
}

func newFilterOpts(vals ...interface{}) filterOpts {
	return filterOpts{
		Version: filterAPIVersion,
		Vals:    vals,
	}
}