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Published: Jan 23, 2023 License: MIT Imports: 34 Imported by: 16


Caire Logo

build Go Reference license Foresight Docs release homebrew caire

Caire is a content aware image resize library based on Seam Carving for Content-Aware Image Resizing paper.



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How does it work

  • An energy map (edge detection) is generated from the provided image.
  • The algorithm tries to find the least important parts of the image taking into account the lowest energy values.
  • Using a dynamic programming approach the algorithm will generate individual seams across the image from top to down, or from left to right (depending on the horizontal or vertical resizing) and will allocate for each seam a custom value, the least important pixels having the lowest energy cost and the most important ones having the highest cost.
  • We traverse the image from the second row to the last row and compute the cumulative minimum energy for all possible connected seams for each entry.
  • The minimum energy level is calculated by summing up the current pixel value with the lowest value of the neighboring pixels obtained from the previous row.
  • We traverse the image from top to bottom and compute the minimum energy level. For each pixel in a row we compute the energy of the current pixel plus the energy of one of the three possible pixels above it.
  • Find the lowest cost seam from the energy matrix starting from the last row and remove it.
  • Repeat the process.
The process illustrated:
Original image Energy map Seams applied
original sobel debug


Key features which differentiates this library from the other existing open source solutions:

  • GUI progress indicator
  • Customizable command line support
  • Support for both shrinking or enlarging the image
  • Resize image both vertically and horizontally
  • Face detection to avoid face deformation
  • Support for multiple output image type (jpg, jpeg, png, bmp, gif)
  • Support for stdin and stdout pipe commands
  • Can process whole directories recursively and concurrently
  • Use of sobel threshold for fine tuning
  • Use of blur filter for increased edge detection
  • Support for squaring the image with a single command
  • Support for proportional scaling
  • Support for protective mask
  • Support for removal mask
  • GUI debug mode support


First, install Go, set your GOPATH, and make sure $GOPATH/bin is on your PATH.

$ go install 

MacOS (Brew) install

The library can also be installed via Homebrew.

$ brew install caire


$ caire -in input.jpg -out output.jpg

Supported commands:

$ caire --help

The following flags are supported:

Flag Default Description
in - Input file
out - Output file
width n/a New width
height n/a New height
preview true Show GUI window
perc false Reduce image by percentage
square false Reduce image to square dimensions
blur 4 Blur radius
sobel 2 Sobel filter threshold
debug false Use debugger
face false Use face detection
angle float Plane rotated faces angle
mask string Mask file path
rmask string Remove mask file path
color string Seam color (default #ff0000)
shape string Shape type used for debugging: circle,line (default circle)

Face detection

The library is capable of detecting human faces prior resizing the images by using the lightweight Pigo ( face detection library.

The image below illustrates the application capabilities for human face detection prior resizing. It's clearly visible that with face detection activated the algorithm will avoid cropping pixels inside the detected faces, retaining the face zone unaltered.

Original image With face detection Without face detection
Original With Face Detection Without Face Detection

Sample image source

GUI progress indicator

GUI preview

A GUI preview mode is also incorporated into the library for in time process visualization. The Gio GUI library has been used because of its robustness and modern architecture. Prior running it please make sure that you have installed all the required dependencies noted in the installation section ( .

The preview window is activated by default but you can deactivate it any time by setting the -preview flag to false. When the images are processed concurrently from a directory the preview mode is deactivated.

Face detection to avoid face deformation

In order to detect faces prior rescaling, use the -face flag. There is no need to provide a face classification file, since it's already embedded into the generated binary file. The sample code below will resize the provided image with 20%, but checks for human faces in order tot avoid face deformations.

For face detection related settings please check the Pigo documentation.

$ caire -in input.jpg -out output.jpg -face=1 -perc=1 -width=20

Support for stdin and stdout pipe commands

You can also use stdin and stdout with -:

$ cat input/source.jpg | caire -in - -out - >out.jpg

in and out default to - so you can also use:

$ cat input/source.jpg | caire >out.jpg
$ caire -out out.jpg < input/source.jpg

You can provide also an image URL for the -in flag or even use curl or wget as a pipe command in which case there is no need to use the -in flag.

$ caire -in <image_url> -out <output-folder>
$ curl -s <image_url> | caire > out.jpg

Process multiple images from a directory concurrently

The library can also process multiple images from a directory concurrently. You have to provide only the source and the destination folder and the new width or height in this case.

$ caire -in <input_folder> -out <output-folder>

Support for multiple output image type

There is no need to define the output file type, just use the correct extension and the library will encode the image to that specific type. You can export the resized image even to a Gif file, in which case the generated file shows the resizing process interactively.

Other options

In case you wish to scale down the image by a specific percentage, it can be used the -perc boolean flag. In this case the values provided for the width and height are expressed in percentage and not pixel values. For example to reduce the image dimension by 20% both horizontally and vertically you can use the following command:

$ caire -in input/source.jpg -out ./out.jpg -perc=1 -width=20 -height=20 -debug=false

Also the library supports the -square option. When this option is used the image will be resized to a square, based on the shortest edge.

When an image is resized on both the X and Y axis, the algorithm will first try to rescale it prior resizing, but also will preserve the image aspect ratio. The seam carving algorithm is applied only to the remaining points. Ex. : given an image of dimensions 2048x1536 if we want to resize to the 1024x500, the tool first rescale the image to 1024x768 and then will remove only the remaining 268px.

Masks support:

  • -mask: The path to the protective mask. The mask should be in binary format and have the same size as the input image. White areas represent regions where no seams should be carved.
  • -rmask: The path to the removal mask. The mask should be in binary format and have the same size as the input image. White areas represent regions to be removed.
Mask Mask removal

Caire integrations

snapcraft caire


Shrunk images
Original Shrunk
broadway_tower_edit broadway_tower_edit
waterfall waterfall
dubai dubai
boat boat
Enlarged images
Original Extended
gasadalur gasadalur
dubai dubai

Useful resources



Copyright © 2018 Endre Simo

This project is under the MIT License. See the LICENSE file for the full license text.



Package caire is a content aware image resize library, which can rescale the source image seamlessly both vertically and horizontally by eliminating the less important parts of the image.

The package provides a command line interface, supporting various flags for different types of rescaling operations. To check the supported commands type:

$ caire --help

In case you wish to integrate the API in a self constructed environment here is a simple example:

package main

import (

func main() {
	p := &caire.Processor{
		// Initialize struct variables

	if err := p.Process(in, out); err != nil {
		fmt.Printf("Error rescaling image: %s", err.Error())



This section is empty.


This section is empty.


This section is empty.


type C added in v1.4.4

type C = layout.Context

type Carver

type Carver struct {
	Points []float64
	Seams  []Seam
	Width  int
	Height int

Carver is the main entry struct having as parameters the newly generated image width, height and seam points.

func NewCarver

func NewCarver(width, height int) *Carver

NewCarver returns an initialized Carver structure.

func (*Carver) AddSeam

func (c *Carver) AddSeam(img *image.NRGBA, seams []Seam, debug bool) *image.NRGBA

AddSeam add a new seam.

func (*Carver) ComputeSeams

func (c *Carver) ComputeSeams(p *Processor, img *image.NRGBA) (*image.NRGBA, error)

ComputeSeams compute the minimum energy level based on the following logic:

  • traverse the image from the second row to the last row and compute the cumulative minimum energy M for all possible connected seams for each entry (i, j).

  • the minimum energy level is calculated by summing up the current pixel value with the minimum pixel value of the neighboring pixels from the previous row.

func (*Carver) FindLowestEnergySeams

func (c *Carver) FindLowestEnergySeams(p *Processor) []Seam

FindLowestEnergySeams find the lowest vertical energy seam.

func (*Carver) Grayscale added in v1.3.1

func (c *Carver) Grayscale(src *image.NRGBA) *image.NRGBA

Grayscale converts the source image to grayscale mode.

func (*Carver) RemoveSeam

func (c *Carver) RemoveSeam(img *image.NRGBA, seams []Seam, debug bool) *image.NRGBA

RemoveSeam remove the least important columns based on the stored energy (seams) level.

func (*Carver) RotateImage270

func (c *Carver) RotateImage270(src *image.NRGBA) *image.NRGBA

RotateImage270 rotate the image by 270 degree counter clockwise.

func (*Carver) RotateImage90

func (c *Carver) RotateImage90(src *image.NRGBA) *image.NRGBA

RotateImage90 rotate the image by 90 degree counter clockwise.

func (*Carver) SobelDetector added in v1.4.0

func (c *Carver) SobelDetector(img *image.NRGBA, threshold float64) *image.NRGBA

SobelDetector uses the sobel filter operator for detecting image edges. See

func (*Carver) StackBlur added in v1.3.3

func (c *Carver) StackBlur(img *image.NRGBA, radius uint32) *image.NRGBA

StackBlur applies a blur filter to the provided image. The radius defines the bluring average.

type D added in v1.4.4

type D = layout.Dimensions

type Gui added in v1.4.1

type Gui struct {
	// contains filtered or unexported fields

Gui is the basic struct containing all of the information needed for the UI operation. It receives the resized image transferred through a channel which is called in a separate goroutine.

func NewGUI added in v1.4.4

func NewGUI(w, h int) *Gui

NewGUI initializes the Gio interface.

func (*Gui) Add added in v1.4.5

func (g *Gui) Add(index int, title string, enabled bool)

Add adds a new hud control for debugging.

func (*Gui) DrawSeam added in v1.4.1

func (g *Gui) DrawSeam(shape string, x, y, dim float32)

DrawSeam visualizes the seam carver in action when the preview mode is activated. It receives as parameters the shape type, the seam (x,y) coordinates and a dimension.

func (*Gui) EncodeSeamToImg added in v1.4.1

func (g *Gui) EncodeSeamToImg()

EncodeSeamToImg draws the seams into an image widget.

func (*Gui) Run added in v1.4.1

func (g *Gui) Run() error

Run is the core method of the Gio GUI application. This updates the window with the resized image received from a channel and terminates when the image resizing operation completes.

type Processor

type Processor struct {
	SobelThreshold   int
	BlurRadius       int
	NewWidth         int
	NewHeight        int
	Percentage       bool
	Square           bool
	Debug            bool
	Preview          bool
	FaceDetect       bool
	ShapeType        string
	SeamColor        string
	MaskPath         string
	RMaskPath        string
	Mask             *image.NRGBA
	RMask            *image.NRGBA
	GuiDebug         *image.NRGBA
	FaceAngle        float64
	PigoFaceDetector *pigo.Pigo
	Spinner          *utils.Spinner
	// contains filtered or unexported fields

Processor options

func (*Processor) Dither added in v1.4.5

func (p *Processor) Dither(src *image.NRGBA) *image.NRGBA

Dither converts an image to black and white image, where the white is fully transparent.

func (*Processor) Grayscale added in v1.4.0

func (p *Processor) Grayscale(src *image.NRGBA) *image.NRGBA

Grayscale converts the image to grayscale mode.

func (*Processor) Process

func (p *Processor) Process(r io.Reader, w io.Writer) error

Process encodes the resized image into an io.Writer interface. We are using the io package, since we can provide different input and output types, as long as they implement the io.Reader and io.Writer interface.

func (*Processor) Resize

func (p *Processor) Resize(img *image.NRGBA) (image.Image, error)

Resize is the main entry point for the image resize operation. The new image can be resized either horizontally or vertically (or both). Depending on the provided options the image can be either reduced or enlarged.

type Seam

type Seam struct {
	X int
	Y int

Seam struct contains the seam pixel coordinates.

type SeamCarver

type SeamCarver interface {
	Resize(*image.NRGBA) (image.Image, error)

SeamCarver interface defines the Resize method. This needs to be implemented by every struct which declares a Resize method.


Path Synopsis
It is mainly used to debug the seam carving operation correctness with face detection and image mask enabled.
It is mainly used to debug the seam carving operation correctness with face detection and image mask enabled.

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