imgix-php is a client library for generating image URLs with imgix. It is tested under PHP versions 8.0, 8.1 and 8.2.

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• Installation
• Usage
• Signed URLs
• Srcset Generation
  • Fixed-Width Images
    • Variable Quality
  • Fluid-Width Images
    • Custom Widths
    • Width Ranges
    • Width Tolerance
• The ixlib Parameter
• License

Installation

You can install the package via composer:

composer require imgix/imgix-php

Usage

To begin creating imgix URLs programmatically, add the php files to your project. The URL builder can be reused to create URLs for any images on the domains it is provided.

use Imgix\UrlBuilder;

$builder = new UrlBuilder("demos.imgix.net");
$params = array("w" => 100, "h" => 100);
echo $builder->createURL("bridge.png", $params);
// 'https://demos.imgix.net/bridge.png?h=100&w=100'

HTTPS support is available by default. However, if you need HTTP support, call setUseHttps on the builder:

use Imgix\UrlBuilder;

$builder = new UrlBuilder("demos.imgix.net");
$builder->setUseHttps(false);
$params = array("w" => 100, "h" => 100);
echo $builder->createURL("bridge.png", $params);
// 'http://demos.imgix.net/bridge.png?h=100&w=100'

Signed URLs

To produce a signed URL, you must enable secure URLs on your source and then provide your signature key to the URL builder.

use Imgix\UrlBuilder;

$builder = new UrlBuilder("demos.imgix.net");
$builder->setSignKey("test1234");
$params = array("w" => 100, "h" => 100);
echo $builder->createURL("bridge.png", $params);
// 'http://demos.imgix.net/bridge.png?h=100&w=100&s=bb8f3a2ab832e35997456823272103a4'

Srcset Generation

The imgix-php package allows for generation of custom srcset attributes, which can be invoked through the createSrcSet method. By default, the generated srcset will allow for responsive size switching by building a list of image-width mappings.

$builder = new UrlBuilder("demos.imgix.net", true, "my-key", false);
echo $builder->createSrcSet("image.png");

The above will produce the following srcset attribute value which can then be served to the client:

https://demos.imgix.net/image.png?w=100&s=e415797545a77a9d2842dedcfe539c9a 100w,
https://demos.imgix.net/image.png?w=116&s=b2da46f5c23ef13d5da30f0a4545f33f 116w,
https://demos.imgix.net/image.png?w=135&s=b61422dead929f893c04b8ff839bb088 135w,
                                        ...
https://demos.imgix.net/image.png?w=7401&s=ad671301ed4663c3ce6e84cb646acb96 7401w,
https://demos.imgix.net/image.png?w=8192&s=a0fed46e2bbcc70ded13dc629aee5398 8192w

Fixed-Width Images

In cases where enough information is provided about an image's dimensions, createSrcSet will instead build a srcset that will allow for an image to be served at different resolutions. The parameters taken into consideration when determining if an image is fixed-width are w and h.

By invoking createSrcSet with either a width or height provided, a different srcset will be generated for a fixed-width image instead.

$builder = new UrlBuilder("demos.imgix.net", true, "my-key", false);
echo $builder->createSrcSet("image.png", array("h"=>800, "ar"=>"3:2", "fit"=>"crop"));

Will produce the following attribute value:

https://demos.imgix.net/image.png?ar=3%3A2&dpr=1&fit=crop&h=800&s=6cf5c443d1eb98bc3d96ea569fcef088 1x,
https://demos.imgix.net/image.png?ar=3%3A2&dpr=2&fit=crop&h=800&s=d60a61a5f34545922bd8dff4e53a0555 2x,
https://demos.imgix.net/image.png?ar=3%3A2&dpr=3&fit=crop&h=800&s=590f96aa426f8589eb7e449ebbeb66e7 3x,
https://demos.imgix.net/image.png?ar=3%3A2&dpr=4&fit=crop&h=800&s=c89c2fd3148957647e86cfc32ba20517 4x,
https://demos.imgix.net/image.png?ar=3%3A2&dpr=5&fit=crop&h=800&s=3d73af69d78d49eef0f81b4b5d718a2c 5x

For more information to better understand srcset, we highly recommend Eric Portis' "Srcset and sizes" article which goes into depth about the subject.

Variable Quality

This library will automatically append a variable q parameter mapped to each dpr parameter when generating a fixed-width image srcset. This technique is commonly used to compensate for the increased file size of high-DPR images.

Since high-DPR images are displayed at a higher pixel density on devices, image quality can be lowered to reduce overall file size––without sacrificing perceived visual quality. For more information and examples of this technique in action, see this blog post.

This behavior will respect any overriding q value passed in as a parameter. Additionally, it can be disabled altogether by passing $disableVariableQuality = true to createSrcSet()'s $options.

This behavior specifically occurs when a fixed-width image is rendered, for example:

// Note that `params=array("w" => 100)` allows `createSrcSet` to _infer_ the creation
// of a DPR based srcset attribute for fixed-width images.
$builder = new UrlBuilder("demos.imgix.net", true, "", false);
$params = array("w" => 100);
$srcset = $builder->createSrcSet($path="image.jpg", $params=$params);

The above will generate a srcset with the following q to dpr query params:

https://demos.imgix.net/image.jpg?dpr=1&q=75&w=100 1x,
https://demos.imgix.net/image.jpg?dpr=2&q=50&w=100 2x,
https://demos.imgix.net/image.jpg?dpr=3&q=35&w=100 3x,
https://demos.imgix.net/image.jpg?dpr=4&q=23&w=100 4x,
https://demos.imgix.net/image.jpg?dpr=5&q=20&w=100 5x'

Fluid-Width Images

Custom Widths

In situations where specific widths are desired when generating srcset pairs, a user can specify them by passing an array of positive integers as 'widths' within the $options array:

$builder = new UrlBuilder("demos.imgix.net", true, "", false);
$opts = array('widths' => array(144, 240, 320, 446, 640));
$srcset = $builder->createSrcSet($path="image.jpg", $params=array(), $options=$opts);

https://demos.imgix.net/image.jpg?w=144 144w,
https://demos.imgix.net/image.jpg?w=240 240w,
https://demos.imgix.net/image.jpg?w=320 320w,
https://demos.imgix.net/image.jpg?w=446 446w,
https://demos.imgix.net/image.jpg?w=640 640w

Note: in situations where a srcset is being rendered as a fixed-width srcset, any custom widths passed in will be ignored.

Additionally, if both widths and a width tolerance are passed to the createSrcSet method, the custom widths list will take precedence.

Width Ranges

In certain circumstances, you may want to limit the minimum or maximum value of the non-fixed srcset generated by the createSrcSet method. To do this, you can specify the widths at which a srcset should start and stop:

$builder = new UrlBuilder("demo.imgix.net", true, "", false);
$opts = array('start' => 500, 'stop' => 2000);
$srcset = $builder->createSrcSet($path="image.jpg", $params=array(), $options=$opts);

Formatted version of the above srcset attribute:

https://demo.imgix.net/image.jpg?w=500 500w,
https://demo.imgix.net/image.jpg?w=580 580w,
https://demo.imgix.net/image.jpg?w=673 673w,
https://demo.imgix.net/image.jpg?w=780 780w,
https://demo.imgix.net/image.jpg?w=905 905w,
https://demo.imgix.net/image.jpg?w=1050 1050w,
https://demo.imgix.net/image.jpg?w=1218 1218w,
https://demo.imgix.net/image.jpg?w=1413 1413w,
https://demo.imgix.net/image.jpg?w=1639 1639w,
https://demo.imgix.net/image.jpg?w=1901 1901w,
https://demo.imgix.net/image.jpg?w=2000 2000w

Width Tolerance

The srcset width tolerance dictates the maximum tolerated difference between an image's downloaded size and its rendered size.

For example, setting this value to 10 means that an image will not render more than 10% larger or smaller than its native size. In practice, the image URLs generated for a width-based srcset attribute will grow by twice this rate.

A lower tolerance means images will render closer to their native size (thereby increasing perceived image quality), but a large srcset list will be generated and consequently users may experience lower rates of cache-hit for pre-rendered images on your site.

By default, srcset width tolerance is set to 8 percent, which we consider to be the ideal rate for maximizing cache hits without sacrificing visual quality. Users can specify their own width tolerance by providing a positive scalar value as width tolerance:

$builder = new UrlBuilder("demo.imgix.net", true, "", false);
$opts = array('start' => 100, 'stop' => 384, 'tol' => 0.20);
$srcset = $builder->createSrcSet($path="image.jpg", $params=array(), $options=$opts);

In this case, the width tolerance is set to 20 percent, which will be reflected in the difference between subsequent widths in a srcset pair:

https://demo.imgix.net/image.jpg?w=100 100w,
https://demo.imgix.net/image.jpg?w=140 140w,
https://demo.imgix.net/image.jpg?w=196 196w,
https://demo.imgix.net/image.jpg?w=274 274w,
https://demo.imgix.net/image.jpg?w=384 384w

The ixlib Parameter

For security and diagnostic purposes, we sign all requests with the language and version of library used to generate the URL.

This can be disabled by setting setIncludeLibraryParam to False like so:

$builder = new UrlBuilder("demo.imgix.net", true, "", false);
// Or by calling `setIncludeLibraryParam`
$builder->setIncludeLibraryParam(false);

License