July 14, 2021

Lossy vs Lossless Image Compression: What’s the Difference?

If you are looking into optimizing your website’s performance, you will come across some performance techniques such as image compression. Reducing the size of your photos for the web can help you gain precious milliseconds of load time. 

You can choose two types of compression when optimizing your images: lossy and lossless compression. There are pros and cons to both, and you, as a website owner, should evaluate both before making a decision. Don’t worry: we’ve got you covered.

Before we get started, you should know that there is no single best format or “quality setting” for images. It all boils down to which lossy or lossless algorithm is used to optimize each image. Plus, your specific needs. 

Read the article, and you’ll learn everything you should know about the two image compression types.

What Is Lossy Image Compression and How It Works

Lossy compression means that the image size is reduced while some data from the original image file is eliminated. 

If you’re asking if lossy compression is reversible, the answer is: no. The lossy image process is irreversible. Once you have compressed an image this way, you can’t go back. 

Well, you can’t go back in most cases. You’re in luck: With the Imagify WordPress plugin, you’ll be able to revert to your original pictures if you are not satisfied with the results. 

The usual irreversibility of lossy compression begs the question: why should you use it? 

Here’s the thing.

When optimizing data such as source code on a page, it’s critical to ensure that the compression doesn’t alter the code. One piece of bad data and your code can break. For other data types, such as images or video, you can compress it and present an “approximate” representation of the original data without losing its meaning. In other words, no user will notice that your images are compressed (unless you compress the same image over and over).

The truth is, we use lossy image compression all the time on the web.

Lossy Image Formats

The most common lossy image formats are JPEG and GIF. However, our human eyes do not notice the difference between JPEG, GIF, PNG, or other formats. 

Images are great candidates for lossy compression because of the way our eyes work. Our eyes have a different sensitivity to different colors. This is leveraged for image compression as we compress some colors more than others. 

Benefits, Advantages, and Disadvantages of Lossy Compression

At this point, you may be wondering what the pros and cons of lossy compression are. 

The biggest benefit of lossy compression is that it significantly reduces the size of the image file. On the other hand, the biggest disadvantage is that this is achieved with some loss of quality — even though, as we explain, it’s almost imperceptible. Most compression tools available will let you choose the degree of compression used on your images. 

With lossy compression, it’s all about finding a good compromise between file size and image quality.

For instance, Imagify will let you choose between three compression levels: normal, aggressive, and ultra. Aggressive and ultra levels are the powerful ones and will reduce images’ size. At the same time, these levels could somehow reduce images’ quality.

Imagify compression tip: The aggressive level is the most balanced one between reducing image size and not affecting its quality.

When Should You Use Lossy Compression?

Remember that oftentimes a 50% image compression will decrease the file size by 90%.

If you aim to downsize your image file size beyond that, an 80% compression will only yield a 5% decrease, bringing your total reduction to 95%. For most of us, this trade-off is not worth it as the compression may degrade the image to a point where it becomes noticeable

Most online image optimization tools use image compression algorithms to allow them to work around such limitations to provide crisp and clear images that load fast.

Try Imagify for free and see how the plugin works!

Not sure if lossy compression is for you? Run a quick test on a page of your website with Imagify’s image optimizer. That way, you can download compressed images without altering your original images. 

What is Lossless Image Compression and How it Works

Lossless compression means that you reduce the size of an image without any quality loss. Usually, this is achieved by removing unnecessary metadata from JPEG and PNG files. We say “usually” because, with some other compression algorithms, like Imagify’s, other compression opportunities are leveraged without sacrificing the image’s quality. 

Best Lossless Image Formats

The most common lossless image formats are GIF, PNG, and BMP. However, depending on how they are optimized for the web, these formats may see a slight loss in quality. Don’t worry: our eyes won’t be able to pick it up.

Advantages and Benefits of Lossless Compression

The big benefit and advantage of lossless compression are that it allows you to retain the quality of your images while reducing their file size. It’s a win-win: You’ll improve your site performance, and you won’t affect your images’ quality.

When You Should Use Lossless Image Compression

If you are looking to retain the quality of your images, you should choose lossless over lossy compression.

If you choose to go with lossless compression for your images, the trade-off is that you will have larger files. So you will need to find other ways to optimize your website’s performance. Converting your images to the WebP format and choosing the best caching plugin for WordPress could be a good starting point!

Does Image Compression Reduce the Quality?

At this point, you should know that image compression does not necessarily reduce images’ quality. Overall, the image compression that provides some loss of quality is the lossy type. However, it also depends on the image compression algorithm. As long as you find the right compression level, no human eye will detect any drop in photos’ quality.

We recommend you try different solutions according to your needs, as we explain in the next section.

Which Type Of Compression Should You Choose?

Picking the right level of compression depends on many factors. You should consider your needs first and foremost. 

If high-quality images are important to your business and customers, then you should consider lossless compression. However, if your website needs to be incredibly fast, you should consider aggressive image optimization. 

Depending on the CMS you use, you will have certain settings to optimize to ensure that image compression remains under your full control. 

Do not hesitate to look into tools such as WordPress plugins to help you get the job done. 

WordPress Specific Image Compression

If you are using WordPress, you should know that it compresses your images by default. Your JPEG images are compressed at 82 percent when WordPress created preview images. You can increase or decrease the level of compression used by your CMS in the functions.php file. 

We do not recommend this for beginners or intermediate WordPress users. Instead, you should just aim to enhance what WordPress already does in terms of image compression. 

Image Compression For Bloggers

Depending on the type of blog you are running, lossy vs lossless can be turned into a battlefield. You should look into the type of image format you use most often to help you figure out your needs. Here’s a quick recap of the main image formats we tend to use on the web:

  • JPEG – best for photographs or designs with people, places, or things in them. 
  • PNG – best for images with transparent backgrounds
  • GIF – best for animated GIFs. Otherwise, use the JPG format
  • WebP – best format to get smaller images and keep the same quality. Be aware that you have to convert your images to WebP because you can’t upload them on WordPress.

The second thing you have to keep in mind is that you may upload one image, but your CMS will be creating many more. WordPress often creates three to five variations of each image in different sizes. So, image optimization can quickly become a big deal for your blog. 

If you are unsure which route you should go, we recommend picking a lossy compression. Test things out first, of course, to make sure the results are up to your standards. 

Not sure if images are dragging your performance down? Take a page from your website, put it through the online optimizer, and see the results! If you plan to use Google Page Speed Insights, you need to consider that this tool uses one specific algorithm to analyze your images. Sometimes, your images are perfectly optimized with another algorithm that’s not detected by Google’s tool. This can lead to a false-positive result telling you to optimize images that are already optimized.

What’s the Best Image Compression for E-commerce?

Images often account for most of the downloadable bytes on a page. And this tendency has been steadily growing over the years, especially for online stores. Optimizing images can make a difference for an e-commerce website because customers expect to find what they seek fast. The challenge is to find a way to provide high-resolution photos of products for shoppers while keeping load times fast. 

There are many strategies for optimizing photos out there. Image compression tools, photo manipulation, or PHP scripts can often help you achieve the proper performance you seek for your online store. If you are using Shopify, you should know that images are automatically compressed and optimized. If you use WooCommerce, you should rely on a WordPress plugin to optimize images on the fly as you add them to your online store.

Image Optimization for Photographers

If you are a photographer, we recommend you showcase high-quality images. This means turning off the default image compression in WordPress. However, you can still optimize your images with lossless image compression. If you plan to use Imagify, the recommended compression setting is “normal,” which guarantees you will retain the image quality you seek.

Lossy vs Lossless Is a Choice You Make

Find out what you need for your website, test things out and pick what works best for you. Just remember to always keep an eye on the quality of your images and the speed of your load times to make sure you do not lose visitors or customers along the way. 

Imagify, decrease the size of your images, increase the speed of your website: try it for free
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