README

Automatic detection of maximum compression without visually changing the image.

Overview

This is a library which attempts to determine the maximum amount of compression which can be applied to an image while not introducing any visible changes.

The output is an integer between 0 and 100.

Installation

composer require freshleafmedia/image-compression-finder

DSSIM

A working copy of kornelski/dssim must be installed.

To install the latest, at time of writing, on Ubuntu the following one-liner can be used:

curl -sSL https://github.com/kornelski/dssim/releases/download/3.2.3/dssim_3.2.3_amd64.deb > /tmp/dssim.deb && apt install /tmp/dssim.deb

Imagick/GD

Either of Imagick or GD extensions are required.

Usage

use FreshleafMedia\ImageCompressionFinder\ImageCompressionFinder;

$quality = ImageCompressionFinder::make()->run('/path/to/image');

$quality; // 66 (0-100)

How it works

The algorithm uses a binary search to repeatedly compress and test an image until the ideal quality is found

1. Compress the image with a quality setting of 60
2. Analyse the new image using DSSIM
3. If the change is within tolerance the quality is halved, if not it is increased by 50% (aka a binary search)
4. Compress the image again with the new quality
5. GOTO 2

Options

There are a couple of configuration options:

$quality = ImageCompressionFinder::make()
    ->maxDifference(0.001) // The highest acceptable visual change. 0-∞ where 0 is no change at all
    ->startingQuality(60) // Where to start the search
    ->driver('imagick') // The driver to use to compress images. Eg imagick or gd
    ->run();

Tests

Unit tests can be run via composer test

License

See LICENSE