autocrop

README

autocrop

autocrop is an automatic image cropping/region-of-interest finding implementation in Go.

autocrop uses an energy-based approach to determine regions of visual interest at which to stop cropping. Cropping is alpha channel aware and supports images with translucency.

autocrop currently assumes image data is sRGB encoded.

See the API documentation for more details.

Some examples of cropping decisions made by autocrop can be seen here:

Threshold 0.3

Threshold 0.1

Threshold 0.15

This software is made available under an MIT license.

Example usage

Find the autocropped bounds of an image using BoundsForThreshold:

croppedBounds := autocrop.BoundsForThreshold(img, energyThreshold)

The energyThreshold is a value between 0.0 and 1.0 which determines at what energy level cropping stops, relative to the maximum energy of the image. Higher threshold values result in more aggressive cropping.

The ToThreshold function can be used to conveniently get a cropped image if you don’t need the bounds:

croppedImg := autocrop.ToThreshold(img, energyThreshold)

New

Option to add margin to the cropped image. Margin follows the same rules as CSS's margin.

• When one value is specified, it applies the same margin to all four sides.
• When two values are specified, the first margin applies to the top and bottom, the second to the left and right.
• When three values are specified, the first margin applies to the top, the second to the right and left, the third to the bottom.
• When four values are specified, the margins apply to the top, right, bottom, and left in that order (clockwise).

croppedImg := autocrop.ToThresholdWithMargin(img, energyThreshold, 10)
croppedImg =  autocrop.ToThresholdWithMargin(img, energyThreshold, 10, 5)
croppedImg =  autocrop.ToThresholdWithMargin(img, energyThreshold, 10, 5, 4)
croppedImg =  autocrop.ToThresholdWithMargin(img, energyThreshold, 10, 5, 4, 2)

Command line tool

autocrop also provides a command line tool that can be installed as follows:

$ go install github.com/chris-dot-exe/autocrop/cmd/autocrop

and used to crop images like this:

$ autocrop <input_image> <output_png> [threshold]

The threshold is optional and defaults to 0.1.

Documentation

Index

• func BoundsForThreshold(img *image.NRGBA, energyThreshold float32) image.Rectangle
• func BoundsForThresholdWithMargin(img *image.NRGBA, energyThreshold float32, extend bool, margins ...int) (image.Rectangle, srgb.Color)
• func Energies(img *image.NRGBA, r image.Rectangle) (cols, rows []float32, color2 srgb.Color)
• func ToThreshold(img *image.NRGBA, energyThreshold float32) *image.NRGBA
• func ToThresholdWithMargin(img *image.NRGBA, energyThreshold float32, extend bool, margins ...int) *image.NRGBA
• type Margin

Functions

func BoundsForThreshold

func BoundsForThreshold(img *image.NRGBA, energyThreshold float32) image.Rectangle

BoundsForThreshold returns the bounds for a crop of the specified image up to the given energy threshold.

energyThreshold is a value between 0.0 and 1.0 representing the maximum energy to allow to be cropped away before stopping, relative to the maximum energy of the image.

func BoundsForThresholdWithMargin

func BoundsForThresholdWithMargin(img *image.NRGBA, energyThreshold float32, extend bool, margins ...int) (image.Rectangle, srgb.Color)

func Energies

func Energies(img *image.NRGBA, r image.Rectangle) (cols, rows []float32, color2 srgb.Color)

Energies returns the total row and column energies for the specified region of an image.

func ToThreshold

func ToThreshold(img *image.NRGBA, energyThreshold float32) *image.NRGBA

ToThreshold returns an image cropped using the bounds provided by BoundsForThreshold.

energyThreshold is a value between 0.0 and 1.0 representing the maximum energy to allow to be cropped away before stopping, relative to the maximum energy of the image.

func ToThresholdWithMargin

func ToThresholdWithMargin(img *image.NRGBA, energyThreshold float32, extend bool, margins ...int) *image.NRGBA

Types

type Margin

type Margin struct {
	Top    int
	Right  int
	Left   int
	Bottom int
}