A selection of image manipulation tools. Each tool requires an input file from stdin, either .png, .jpeg or .gif. They always output a .png file, regardless of input type, using stdout.

Requires Go 1. Install to $GOPATH/bin with,

$ go install github.com/hawx/img

Use go help and go help [command] for information.

Allows you to blend two images together using a blend mode. Takes one image from STDIN (the base image, imagine the bottom layer in photoshop) and one image as an argument (the blend image, the layer above).

$ img blend --screen blend.png --opacity 0.3 < input.png > output.png

Tool to blur images. Can do a Gaussian or Box blur.

$ img blur --style wrap --box --radius 30 < input.png > output.ong

Adjust the value of each colour channel individually. This tool can modify the following channels: red, green, blue, hue, saturation, lightness, brightness and alpha.

$ img channel --red --green --ratio 1.1 < input.png > output.png

Adjusts the contrast of the given image.

$ img contrast --by -25 < input.png > output.png

Perform gamma correction on an image.

$ img gamma < input.png > output.png

Creates a greyscale version of an image.

$ img greyscale --average < input.png > output.png

An (almost; that is I'm not sure this is exactly the same) implementation of the equilateral triangle filter from pxl app.

$ img hxl --width 50 < input.png > output.png

Allows you to alter the levels of an image. You can set (or auto set) white and black points, or pass a curve to use, along with the channels to act on.

$ img levels --red --green --curve "0,20 50,40 100,100" < input.png > output.png

Pixelates an image. Use --size HxW to set pixel size used.

$ img pixelate --size 10x50 < input.png > output.png

Implementation of the triangle filter from pxl app, using the algorithm loosely described by revdancatt.

$ img pxl --size 30x30 < input.png > output.png

Randomly shuffles pixels around the image. Use -v or -h to constrain it to vertical or horizontal shuffling, respectively.

$ img shuffle --vertical < input.png > output.png

Tint an image with a colour.

$ img tint --with '#222b6d33' < input.png > output.png

Pixelate an image into isometric cubes with (simplistic) fake lighting.

$ img vxl --rows 14 < input.png > output.png

These tools have been created to do one task each, and to use standard input/output so that they can be easily composed. For example;

$ (img shuffle --horizontal | img hxl | img hue --by -20) < input.png > output.png

It is possible to extend img with external scripts. They must be named img-something, and be somewhere on your $PATH. They must also respond to the flags --usage, --short and --long so they can be integrated into img help.

As an example of an external script, here is img-lomo, that applies a lomography effect detailed in Lomography, UNIX Style. It makes use of imagemagick to generate a mask, then blends the images with img.

#!/usr/bin/env sh

function usage {
  echo "lomo [options]"
}

function short {
  echo "applies a simple lomo effect to the image."
}

function long {
  echo "  Applies a simple lomo effect to the image, boosting its saturation and
  composing with a black edged mask."
}

case "$1" in
  --usage ) usage
    exit
    ;;
  --short ) short
    exit
    ;;
  --long ) long
    exit
    ;;
esac

# Using the method described on:
# http://the.taoofmac.com/space/blog/2005/08/23/2359

# generate a mask using imagemagick
convert -size 80x60 xc:black \
        -fill white -draw 'rectangle 1,1 78,58' \
        -gaussian 7x15 +matte lomo_mask.png
mogrify -resize 800x600 -gaussian 0x5 lomo_mask.png

# then put it together with img
(
  img contrast --ratio 1.2 |
  img saturation --ratio 1.2 |
  img blend --multiply --fit lomo_mask.png
)

# delete the mask
rm lomo_mask.png

See this gist for a pure Go rewrite of this.

You can easily use img in programmatically as well,

$ go get github.com/hawx/img
$ cat > greyscaler.go
package main

import (
  "github.com/hawx/img/greyscale"
  "os"
  "image/png"
)

func main() {
  file, _ := os.Open(os.Args[1])
  img,  _ := png.Decode(file)

  img = greyscale.Average(img)

  out, _ := os.Create(os.Args[2])
  png.Encode(out, img)
}

$ go build greyscaler.go
$ ./greyscaler input.png output.png

To view documentation run godoc -http=:8080 then navigate to http://localhost:8080/pkg/github.com/hawx/img/, or see it on GoPkgDoc.