The use of images can enhance the content of your website. However, file compression is critical to prevent them from taking up unnecessary disk space and hurting your site’s performance. To ensure that you are properly optimizing your images, it helps to understand the difference between lossy vs lossless (lossy and lossless) compression.

In this post, we will 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 get started!

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What is lossy compression?
Lossy compression reduces file size by removing as much data as possible. As a result, it can cause degradation that reduces image quality. In any case, 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 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 original at 389 KB. The image on the right has a 95% reduction in size:

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

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

Pros and cons of lossy compression
The main advantages of lossy compression are data elimination and size reduction. Creating smaller file sizes can improve the performance and loading time of your site. In turn, this can improve your user experience (UX) and search engine optimization (SEO) .

On the other hand, there are some drawbacks of lossy compression. First, you cannot restore files to their original form. In other words, the process is irreversible. In addition, the deletion of data can affect the quality of the image.

Lossy compression is a trade-off: the smaller the file size, the greater the performance. However, the more data that is lost, the more the image quality will suffer.

What is lossless compression?
Unlike lossy compression, lossless compression does not remove critical data from the image file. Instead, it removes metadata and non-essential information that does not affect the appearance or quality of the image. Although this compression method can help reduce file size slightly, the difference is usually not significant.

Two popular file formats associated with lossless compression are zipped archived files (ZIP) 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, such as 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. Also, unlike lossy compression you can restore an image to its original format without any loss of data.

However, there is a significant downside: lossless compression has a lower data retention capacity. Since this compression method does not reduce the size of the data, you will not 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.

We recommend that you use lossless compression for PNGs. In contrast, lossy is more suitable for JPEGs.

WordPress automatically compresses JPEG images (reducing the file size 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 . In any case, we do not recommend this method unless you are familiar 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 such as Adobe Photoshop or a WordPress image optimization plugin such as Imagify , WP Smush or ShortPixel .

You can also use a free online tool such as 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 have 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 is 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. The loss of data is largely unnoticeable, but it can greatly improve loading times. Therefore, this method is ideal for e-commerce shops, portfolio sites and blogs.

Lossy compression can optimize images and product 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. Also, you can usually choose the level of compression.

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

Lossy compression is best for WordPress images because most people will not see the reduction in quality. Our eyes have varying sensitivity to colors and brightness . Compression algorithms take advantage of the way humans process images to make data removal and quality reduction almost undetectable.

When to use lossless compression in WordPress
Generally, lossless compression is best for images with heavy text and images with transparent backgrounds. We recommend it for RAW, BMP, GIF and PNG file formats.

If image quality reduction is an issue, you may be better off opting 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. In that case, you can optimize your images and site performance by using other methods, such as leveraging a content delivery network (CDN) .

Conclusion
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, you won’t want to harm 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 Web sites because it can significantly reduce file size without removing any obvious data. However, lossless compression may be better if you are more concerned about image quality than loading times.