A selection of image manipulation tools

Last update: Dec 29, 2022

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Overview

img

A collection of image manipulation tools. Each tool takes an input file from standard input, this needs to be in PNG, JPEG or GIF format. They output the resulting image (by default in PNG format) to standard output.

To install run,

$ go install hawx.me/code/img

You can then run go help and go help [command] for information.

The aim of img is not to be fast, if you want fast use GraphicsMagick, the aim is to be readable. Diving through endless files of C and C++ to find out how a certain effect is implemented is no fun, reading a single Go file is hopefully better.

Example (Command Line)

Here is an example: First we convert the image to greyscale using the values from the red colour channel, then boost the contrast slightly using a linear function, and finally tint the image with a dark red.

(img greyscale --red | \
  img contrast --linear --ratio 1.5 | \
  img tint --with '#83121344') < input.png > output.png

You can see here how easy it is to chain different tools together using pipes.

Example (Go)

You can also use the img libraries in Go code. We could rewrite the previous example as,

// example.go
package main

import (
  "hawx.me/code/img/contrast"
  "hawx.me/code/img/greyscale"
  "hawx.me/code/img/tint"

  "image/png"
  "os"
)

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

  img = greyscale.Red(img)
  img = contrast.Linear(img, 1.5)
  img = tint.Tint(img, color.NRGBA{131, 18, 19, 255})

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

This can then be compiled and run like ./example input.png output.png.

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Comments

h=0 does not mean black

The implementation of HSLA and HSVA have a small bug where the returned called is black if h == 0, independent of the remaining parameters.

I fixed this, but I did not check for negative h, because I didn't know how you want to handle that :)

opened by surma 1