Understanding the Difference between Lossy and Lossless Data Compression

Using images can enhance the content of your website. However, compressing files is crucial to prevent them from taking up unnecessary disk space and harming your site’s performance. To ensure you optimize your images correctly, it helps to understand the difference between lossy vs lossless (lossy and lossless) compression.

In this post, we’ll start by explaining both clossy and lossless compression. Then we will discuss when to use lossy vs lossless data compression on your WordPress site.

Let’s begin!

What is lossy compression?

Lossy compression reduces file sizes by removing as much data as possible. As a result, it can cause degradation that reduces image quality. However, most of the lost information should not be noticed by visitors when using a balanced compression ratio.

Lossy compression has been developed for a variety of file formats. It is most commonly associated with the JPEG (Joint Photographic Experts Group) and Graphics Interchange Format ( GIF ) formats. You can also use this compression method for audio and video files as well.

Below is an example of an image before and after lossy compression. On the left is the 389 KB original. The image on the right has a 95% size reduction:

As you can see, there is no visible difference in appearance, despite the significant reduction in file size. However, different compression levels can affect the quality of compressed images.

The same principle applies to audio files. For example, you can use loose compression to reduce the size of MP3 files. However, this may reduce the audio quality.

Pros and cons of lossy compression

The main advantages of lossy compression are data elimination and size reduction. Creating smaller files can improve your site’s performance and load times. In turn, this can improve your user experience (UX) and search engine optimization ( SEO ).

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On the other hand, there are some drawbacks of lossy compression. Firstly, it is not possible to restore files to their original form. In other words, the process is irreversible. Additionally, deleting data can degrade image quality.

Lossy compression is a compromise: the smaller the file size, the better the performance. However, the more data is lost, the more image quality will suffer.

What is lossless compression?

Unlike lossy compression, lossless compression does not remove critical data from the image file. Instead, it eliminates metadata and non-essential information that doesn’t affect the appearance or quality of the image. While this compression method can help reduce file sizes slightly, the difference is usually not significant.

Two popular file formats associated with lossless compression are archived zipped (ZIP) files and Portable Network Graphics (PNG) images. Lossless compression has been developed for text, images and audio. In fact, some of today’s largest streaming services, like Apple Music and Spotify, use lossless compression for audio files.

Pros and cons of lossless compression

The main advantage of lossless compression is that you don’t have to worry about degrading the quality of an image or making it look pixelated. Furthermore, unlike lossy compression you can restore an image to its original format without any data loss.

However, there is a significant downside: lossless compression has a lower data retention capacity. Since this compression method doesn’t reduce the size of the data, you won’t save as much storage space.

When to use Lossy vs Lossless compression on your WordPress site

The best compression method for your website depends, in part, on the file formats you use. For example, PNGs are best suited for logos, illustrations, icons, and text with transparent backgrounds. However, most standard images on the web are JPEGs.

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We recommend using lossless compression for PNGs. In contrast, lossy is better suited for JPEGs.

WordPress automatically compresses JPEG images  (reducing the file size by up to about 82%) when you upload these images to your media library . You can  adjust this level of compression  by editing your  functions.php file  . However, we don’t recommend this method unless you are comfortable with the code.

Regardless of the default settings, you can further optimize your files with lossy or lossless compression. You can use image editing software like  Adobe Photoshop  or a WordPress image optimization plugin, like  Imagify  ,  WP Smush ,  or  ShortPixel  .

You can also use a free online tool like  TinyPNG  :


Now that we better understand lossy vs lossless compression, it’s time to analyze when it’s best to use each method on your WordPress site. As we’ve seen, both types of compression have unique advantages and disadvantages.

When to use lossy compression in WordPress

If disk space and bandwidth are among your biggest concerns, it’s best to use lossy compression. To speed up your site,  Google recommends lossy compression  via a WordPress plugin. You can also use GZIP compression to further reduce your files.

In most cases, we suggest using lossy compression for WordPress images. Data loss is largely unnoticeable, but can significantly improve loading times. Therefore, this method is ideal for e-commerce shops , portfolio sites and blogs .

Lossy compression can optimize product images and thumbnails in your shop. You can also use it for blog posts and pages with illustrative photos.

Again, depending on the level of compression used, there is usually not a noticeable difference in quality unless you enlarge the images. Additionally, you can typically choose the level of compression.

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The Imagify plugin, for example, lets you select the optimization level based on how aggressive you want the compression to be:

Lossy compression is best for WordPress images because most people won’t see the reduction in quality. Our eyes have variable sensitivity to colors and brightness. Compression algorithms take advantage of the way humans process images to make data deletion and quality reduction almost imperceptible.

When to use lossless compression in WordPress

Typically, lossless compression is best for text-heavy images and images with transparent backgrounds. We recommend it for RAW, BMP, GIF and PNG file formats.

If reduction in image quality is a concern, it may be best to opt for lossless compression. It will keep your images looking sharp while also reducing file size.

Lossless compression might also make sense if your site relies heavily on visual content, such as a photography website. If so, you can optimize your images and site performance using other methods, such as leveraging a  content delivery network (CDN)  .


Optimizing image files is an effective way to improve the speed and performance of your WordPress site. However, it can be difficult to decide between lossy and slossless compression. On the one hand, you probably want to save disk space. On the other hand, you don’t want to damage the look and quality of your content.

As discussed in this post, both lossy and lossless compression have advantages and disadvantages. We recommend lossy compression for most websites as it can significantly reduce file sizes without removing any noticeable data. However, lossless compression might be better if you’re more concerned about image quality than loading times.

Good work.