Converting with ImageMagick

ImageMagick supports AVIF conversion when it has been built with the necessary codec support. With ImageMagick 7, you can convert a JPEG image using the magick command:

magick my-image.jpg -quality 50 my-image.avif

The -quality option controls the encoding quality. Lower values generally produce smaller files, but may introduce more visible compression artifacts.

On systems running ImageMagick 6, the equivalent command is typically:

convert my-image.jpg -quality 50 my-image.avif

Both examples require an ImageMagick installation that supports writing AVIF files.

Converting with ImageMagick from PHP

You can also execute ImageMagick commands directly from PHP using shell_exec():

$source = '/var/www/mysite/images/my-image.jpg';
$destination = '/var/www/mysite/images/my-image.avif';

$command = 'magick '
    . escapeshellarg($source)
    . ' -quality 50 '
    . escapeshellarg($destination)
    . ' 2>&1';

$output = shell_exec($command);

Using escapeshellarg() for each file path is important when constructing shell commands, particularly if the paths originate from user input.

Checking whether a file exists is not a substitute for escaping shell arguments. A filename may contain spaces or shell metacharacters even when it refers to a valid file.

Also remember that shell_exec() does not provide a reliable exit status. For production applications, you should check whether the conversion succeeded and whether the destination file was created correctly. The exec() function can be used when you need the command's exit code.

Read: How to test if a command exists from PHP

Converting directly with PHP GD

Starting with PHP 8.1, the GD Library supports reading and writing AVIF images, provided PHP was built with AVIF support.

You can check whether AVIF is available using:

if (imagetypes() & IMG_AVIF) {
    echo 'AVIF is supported';
}

To convert a JPEG image into AVIF directly with PHP:

$image = imagecreatefromjpeg('my-image.jpg');

if ($image === false) {
    throw new RuntimeException('Unable to load image');
}

if (!imageavif($image, 'my-image.avif', 50)) {
    throw new RuntimeException('Unable to save AVIF image');
}

imagedestroy($image);

The third argument to imageavif() specifies the quality, ranging from 0 to 100. PHP also supports an optional fourth argument to control encoding speed.

GD is convenient when you are already processing images in PHP, although its available encoding options may be more limited than those offered by dedicated image encoders.

Converting PNG files

When I attempted to convert PNG files directly to AVIF, some of the resulting files were actually larger than the originals.

This is not necessarily an error in the conversion process. PNG uses lossless compression and can be particularly efficient for simple graphics, illustrations with limited colors, and certain types of screenshots.

AVIF compression behaves differently, and its efficiency depends on the image content and encoding settings. As a result, some PNG images may become significantly smaller when converted, while others may show little improvement or even increase in size.

In some of my experiments, using WebP as an intermediate format before further conversion appeared to produce smaller files. However, this does not establish that intermediate conversion is inherently more efficient. It may instead reflect differences in encoder behavior or the introduction of additional lossy compression.

Because of the inconsistent results with PNG images, I decided to disable automatic PNG-to-AVIF conversion in my file handler class.

This is a conservative approach, although a more flexible implementation could generate an AVIF version and only use it when the resulting file is actually smaller.

It is also worth remembering that PNG files may already have been optimized using tools such as optipng, pngcrush, or advpng.

JPEG and WebP

Photographs and other complex images are usually good candidates for AVIF conversion. These types of images often benefit significantly from modern lossy compression.

However, if an existing WebP or JPEG image is already small and visually acceptable, the additional savings may not justify the processing time or storage required for another version.

PNG

PNG files should be evaluated individually. Photographic PNG images may benefit considerably from AVIF, while small icons, screenshots, and simple graphics may not.

Both WebP and AVIF support alpha transparency, so transparency alone is not a reason to avoid conversion.

However, if exact pixel reproduction is important, make sure that you use a suitable lossless encoding mode rather than lossy compression.

GIF and animated images

Both WebP and AVIF support animation, making them possible alternatives to animated GIF files.

Animated AVIF is supported by modern browsers, but animation requires additional consideration when converting files. The conversion tool must preserve the frames, timing, and looping behavior of the original animation.

I have not personally tested animated AVIF conversion extensively, so I currently prefer to handle animated files separately instead of automatically converting them.

SVG

SVG is a vector-based image format, unlike raster formats such as JPEG, PNG, WebP, and AVIF.

Vector graphics can scale to different dimensions without losing sharpness, which makes SVG particularly suitable for icons, logos, and illustrations.

Converting SVG to AVIF would rasterize the image, removing its resolution-independent scaling advantages. For this reason, SVG files should generally be preserved in their original format unless there is a specific reason to convert them.