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Lossy vs Lossless Compression

Updated on May 18, 2023
Lossy vs Lossless Compression

In our increasingly digital age, where vast amounts of data are generated and transmitted daily, the importance of efficient compression techniques cannot be overstated. When it comes to reducing the size of your images for the web there are different types of compression you can choose from. In today's post we will look at lossy vs lossless compression and the advantages and disadvantages of both methods. There is no right or wrong method, it comes down to a decision of what you think might work best for your website and environment based on a number of different factors.

The essence of compression

Before we delve into the specifics of lossy and lossless compression, let's first understand the fundamental purpose of compression. At its core, compression is a technique used to reduce the size of data files, making them easier to store, transmit, and manipulate. By eliminating redundancies and non-essential information, compression ensures optimal utilization of resources without compromising data integrity.

Lossy compression

Lossy compression refers to compression in which some of the data from the original file (JPEG) is lost. The process is irreversible, once you convert to lossy, you can't go back. And the more you compress it, the more degradation occurs. JPEGs and GIFs are both lossy image formats. By default WordPress uses a lossy compression rate of 90 percent to optimize JPEG images when creating preview images. You can change this using the filter jpeg_quality in your functions.php file.

One of the biggest obvious benefits to using lossy compression is that it results in a significantly reduced file size (smaller than lossless compression method), but it also means there is quality loss. Most tools, plugins, and software out there will let you choose the degree of compression you want to use. In our example below we took an image and applied different compression ratios to it. You can see there is a big decrease in the size of the images which is great. But you can also see the image degrade in quality as you apply higher ratios of compression.

If you look in the dark gray areas on the middle and far right images it is very noticeable where "compression artifacts" begin to occur. With lossy compression it is about finding a medium ground which you are happy with, for file size and still retaining an acceptable image quality. With 50% compression applied we decreased our image file size by 90%. With 80% compression applied we decreased our image file size by 95%.

Lossy advantages and disadvantages

  • Advantages: Very small file sizes and lots of tools, plugins, and software support it.
  • Disadvantages: Quality degrades with higher ratio of compression. Can't get original back after compressing.

Lossless compression

Lossless compression refers to compression in which the image is reduced without any quality loss. Usually this is done by removing unnecessary metadata from JPEG and PNG files. RAW, BMP, GIF, and PNG are all lossless image formats. It is important to note that since JPEGs are a lossy format that when using the "maximum" preset in Photoshop, this doesn't mean it is lossless. However, even images exported from Photoshop using the "Save for Web" function can still see significant reductions.

The big benefit to lossless compression is that you can retain the quality of your image and still achieve a smaller file size. We took the same image again and ran it through our Optimus Image Optimizer plugin, which uses lossless compression. It also creates progressive JPEGs.

If you look in the dark gray areas this time you can see there is almost no noticeable difference. And we were still able to decrease our file size by 14%. So if you are looking to retain the quality of your images, lossless compression is definitely the way to go.

Lossless advantages and disadvantages

  • Advantages: No loss of quality, slight decreases in image file sizes.
  • Disadvantages: Larger files than if you were to use lossy compression.

The trade-offs: Quality vs size

One of the key distinctions between lossy and lossless compression lies in the trade-off between file size and data quality. Lossless compression ensures the complete preservation of data, making it ideal for scenarios where data integrity is paramount. On the other hand, lossy compression achieves smaller file sizes by selectively discarding non-essential information, leading to a trade-off in quality. It's important to assess the specific requirements of your data to determine which method best suits your needs.

Real-world applications

Both lossless and lossy compression techniques have wide-ranging applications across various industries. Lossless compression is commonly used in archiving, data backup, and secure communication, ensuring the integrity of critical information. Lossy compression, with its ability to dramatically reduce file sizes, is prevalent in multimedia applications such as streaming services, digital photography, and video-sharing platforms. Understanding the specific demands of your data is crucial in selecting the most appropriate compression method.

Factors influencing compression efficiency

The effectiveness of compression algorithms depends on several factors. These include the type of data being compressed, the desired compression ratio, and the computing resources available. Text-based data, for example, can achieve high compression ratios with lossless techniques. Meanwhile, multimedia data, which is more tolerant to slight quality loss, can be efficiently compressed using lossy techniques. It's important to strike the right balance between compression ratio, file size, and the desired level of fidelity.

Lossy-to-lossless transformations

In some cases, lossy and lossless compression can be used in combination to optimize data storage and transmission. A common example is the use of lossy compression for initial compression, followed by lossless compression on the already compressed data. This hybrid approach allows for significant reductions in file size while retaining essential information. It is particularly useful when working with multimedia data that can tolerate a certain degree of loss. However, it's important to note that each transformation introduces a level of data degradation, so careful consideration is required when implementing such techniques.

Making an informed choice

When deciding between lossy and lossless compression, it's crucial to evaluate your specific needs and priorities. Consider the type of data you are working with, the desired compression ratio, the importance of data fidelity, and the available resources. If preserving every detail is paramount and file size is less of a concern, opt for lossless compression. Conversely, if reducing file size is crucial and a slight loss in quality is acceptable, lossy compression may be the more suitable choice.

Evolution of compression techniques

The field of data compression is constantly evolving, driven by advancements in technology and growing demands for efficient data management. New algorithms and techniques are being developed to improve compression ratios, optimize resource utilization, and enhance the quality of compressed data. Staying up-to-date with these developments can help you leverage the latest advancements and make more informed decisions when it comes to data compression.

WebP lossless compression

And of course we can't forget about WebP. This is where combining Google's WebP format along with lossless compression really is powerful! We took the same image again and ran it through our Optimus Image Optimizer plugin, which converts the image to WebP format, using lossless compression.

If you look in the dark gray areas again there is almost no noticeable difference. And this time we were able to decrease our file size by 79%. So if you are looking to retain the quality of your images and still achieve an impressive reduction in file size, you must give WebP a try! You can use our Optimus and Cache Enabler plugins to convert and deliver WebP images in WordPress. Read more about delivering WebP files.

WebP advantages and disadvantages

  • Advantages: No loss of quality, large decreases in file size.
  • Disadvantages: Less browser support, slightly larger file sizes than lossy.


Again when it comes to lossy vs lossless, there is no right or wrong choice. It comes down to what works best for your website and visitors. For example, if you run a photography website, lossless along with the WebP format might be a better way to go as you need your images to be crystal clear and still be reduced in file size. Or you could go the lossy route and use a smaller compression ratio.

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