imgix-java is a client library for generating image URLs with imgix.

---

• Installation
  • Dependencies
  • Install Options
    • Gradle & JCenter
    • Creating a Jar
• Usage
• Signed URLs
• Srcset Generation
  • Fixed-Width Images
  • Fluid-Width Images
    • Custom Widths
    • Width Ranges
    • Width Tolerance
• Running Tests
• License

Installation

Dependencies

The library itself has no external dependencies. Although if you want to build from source (or run tests) then you need ant and the JDK 1.6+.

Install Options

Gradle & JCenter

To add Imgix-Java to your project, include the following in your project's build.gradle:

dependencies {
   compile "com.imgix:imgix-java:2.3.2"
}

And if this is your first external MavenCentral dependency you'll need to add, again to your project level build.gradle, the following:

buildscript {
   repositories {
        mavenCentral()
   }
}

Creating a Jar

To create a jar from source:

gradle build

This creates imgix-java-{VERSION_NUMBER}.jar under ./build/libs

Once a new version has been merged into main on GitHub (don't forget to update the version numbers in build.gradle first!), it can be deployed to Bintray with gradle build && gradle bintrayUpload. After that, the new version can be viewed via the Bintray web interface.

Usage

To begin creating imgix URLs, add the jar to your project's classpath and import the imgix library. The URL builder can be reused to create URLs for any images on the domains it is provided.

import com.imgix.URLBuilder;
import java.util.Map;
import java.util.HashMap;

public class ImgixExample {
    public static void main(String[] args) {
        URLBuilder builder = new URLBuilder("demos.imgix.net");
        Map<String, String> params = new HashMap<String, String>();
        params.put("w", "100");
        params.put("h", "100");
        System.out.println(builder.createURL("bridge.png", params));
        // http://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:

import com.imgix.URLBuilder;
import java.util.Map;
import java.util.HashMap;

public class ImgixExample {
    public static void main(String[] args) {
        URLBuilder builder = new URLBuilder("demos.imgix.net");

        builder.setUseHttps(false); // use http

        Map<String, String> params = new HashMap<String, String>();
        params.put("w", "100");
        params.put("h", "100");
        System.out.println(builder.createURL("bridge.png", params));
        // https://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.

import com.imgix.URLBuilder;
import java.util.Map;
import java.util.HashMap;

public class ImgixExample {
    public static void main(String[] args) {
        URLBuilder builder = new URLBuilder("demos.imgix.net");
        builder.setSignKey("test1234"); // set sign key
        Map<String, String> params = new HashMap<String, String>();
        params.put("w", "100");
        params.put("h", "100");
        System.out.println(builder.createURL("bridge.png", params));
        // http://demos.imgix.net/bridge.png?h=100&w=100&s=bb8f3a2ab832e35997456823272103a4
    }
}

Srcset Generation

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

URLBuilder ub = new URLBuilder("demos.imgix.net", true, "my-token", false);
String srcset = ub.createSrcSet("bridge.png");
System.out.println(srcset);

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

https://demos.imgix.net/bridge.png?w=100&s=494158d968e94ac8e83772ada9a83ad1 100w,
https://demos.imgix.net/bridge.png?w=116&s=6a22236e189b6a9548b531330647ffa7 116w,
https://demos.imgix.net/bridge.png?w=135&s=cbf91f556dd67c0b9e26cb9784a83794 135w,
                                    ...
https://demos.imgix.net/bridge.png?w=7401&s=503e3ba04588f1c301863c9a5d84fe91 7401w,
https://demos.imgix.net/bridge.png?w=8192&s=152551ce4ec155f7a03f60f762a1ca33 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 (width) and h (height).

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

URLBuilder ub = new URLBuilder("demos.imgix.net", true, "my-token", false);
HashMap<String,String> params = new HashMap<String,String> ();
params.put("h", "200");
params.put("ar", "3:2");
params.put("fit", "crop");
String srcset = ub.createSrcSet("bridge.png", params);
System.out.println(srcset);

Will produce the following attribute value:

https://demos.imgix.net/bridge.png?ar=3%3A2&dpr=1&fit=crop&h=200&s=4c79373f535df7e2594a8f6622ec6631 1x,
https://demos.imgix.net/bridge.png?ar=3%3A2&dpr=2&fit=crop&h=200&s=dc818ae4522494f2f750651304a4d825 2x,
https://demos.imgix.net/bridge.png?ar=3%3A2&dpr=3&fit=crop&h=200&s=ba1ec0cef6c77ff02330d40cc4dae932 3x,
https://demos.imgix.net/bridge.png?ar=3%3A2&dpr=4&fit=crop&h=200&s=b51e497d9461be62354c0ea12b6524fb 4x,
https://demos.imgix.net/bridge.png?ar=3%3A2&dpr=5&fit=crop&h=200&s=dc37c1fbee505d425ca8e3764b37f791 5x

For more information to better understand srcset, we 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.

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

URLBuilder ub = new URLBuilder("demo.imgix.net", true, "", false);
HashMap<String, String>  params = new HashMap<String, String>();
params.put("w", "100");
String actual = ub.createSrcSet("image.jpg", params, false);

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

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

URLBuilder ub = new URLBuilder("demo.imgix.net", true, "", false);
HashMap<String, String>  params = new HashMap<String, String>();
Integer[] widths = new Integer[] {144, 240, 320, 446, 640};

String srcset = ub.createSrcSet("image.jpg", params, widths);

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

Note: in situations where a srcset is being rendered as a fixed image, 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 (fluid-width) srcset generated by the createSrcSet method. To do this, you can specify the widths at which a srcset should begin and end:

URLBuilder ub = new URLBuilder("demo.imgix.net", true, "", false);
HashMap<String, String>  params = new HashMap<String, String>();
String actual = ub.createSrcSet("image.jpg", params, 500, 2000);

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 0.1 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 0.08 (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:

URLBuilder ub = new URLBuilder("test.imgix.net", false, "", false);
HashMap<String, String>  params = new HashMap<String, String>();
String srcset = ub.createSrcSet("image.png", params, 100, 384, 0.20);

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

Running Tests

To run tests clone this project and run:

gradle test

Dependencies for running tests (junit, etc) are provided (in test/lib and referenced in the build config).

License