It is important to make websites fast and responsive for users. One of the best and easiest ways to speed up a website is to compress images. Use Caesium and Squoosh to optimize images.
There are many more tools for compressing images for use online, but I want to highlight these two because they are so different. I have been using Squoosh for a long time, but I came across Caesium recently, and it has advantages over its rival image compressor.
If you want to know whether your website is fast enough or whether visitors are likely to be annoyed with its slow speed, use a tool like GTmetrix. Enter the URL of a typical page on your site and see how long it takes to load. How long should a page on a website take to load? There is no exact figure, and you should simply make it as fast as you can. Three or four seconds of load time is OK. Not good, but not bad. I have seen popular sites with 10+ second load times.
Whatever your site’s load time, optimizing images by shrinking the file size only has benefits. There are plugins like Imagify, Smush, Shortpixel Image Optimizer, and others. However, it is best to upload an optimized image in the first place rather than upload bloated image files, cross your fingers, and hope the plugin can do something with it.
Free image compression
Caesium Image Compressor and Squoosh are both free tools, and the source code is available for them on GitHub if you want to check them out or modify them. Most people will simply use the ready-made tools online or offline on their computer.
Online image compression
Both Squoosh and Caesium can be used online by going to their websites in a browser. This means that it works on Windows PCs, Apple Macs, and Linux. However, there are big differences in the features provided.
Caesium Image Compressor
Caesium online image compressor is a simple tool with only basic options. However, it accepts multiple files. Up to five images can be dragged from an Explorer window on a PC or Finder on a Mac and dropped on the web page to add them to a list of images to be processed. There is a file size limit of 10 MB, and only JPG, PNG, GIF, and WebP file formats are accepted. This is fine.
Choose between quality and size. Files are output as JPG images, and you could set a JPEG quality of 80, for example. Or you could set a maximum file size, like 200 K. Whatever compression is required to get the image under the maximum file size will be applied. There is a Lossless Compression switch. Ignore it for web images. It does keep the image quality but has only a small file size saving.
After compressing the images, which takes no more than a few seconds, they can be downloaded and saved to the computer. The file size savings depend on how much compression is used, but there is the usual JPEG tradeoff between size and quality.
There are two drawbacks. One is that only JPG files can be output and there is no WebP option. Another drawback is that you cannot preview the images before compressing them. You must guess how much compression to use, and if it is not right, you must compress the images again with new settings.
Squoosh
Squoosh is the opposite of Caesium in many ways, and it can only process one image at a time. However, it provides numerous settings and options that enable you to customize the image compression settings to get the best results. It will take you longer to process a collection of images, but it is worth it.
An image file can be dragged and dropped onto the Squoosh web page to load it. A panel appears in the bottom-right corner with options and settings. Simple settings are shown by default, but advanced options are available by expanding the panel. All popular web image file formats are supported, and it is useful to switch between them and see which produces the smallest file size. Compare PNG, JPG, and WebP, for example, to see which is best.
There is a preview feature that uses a draggable vertical divider that shows before and after optimization. This is very useful. You can experiment with settings, like compression levels, and immediately see how the image will be affected. You get what you see, so you are always happy with the resulting image. The file sie and percentage saving is displayed.
Caesium online image compressor is useful for optimizing multiple JPEGs, but Squoosh produces better results by enabling you to optimize each image separately and select the best optimization parameters and file format.
Offline image compression
The Squoosh website can be installed on a computer by clicking the Install button in the top-right corner of the page. It is not a true app, but a web app, which is a website designed to look like a desktop app. It has exactly the same features as the website, so it is just as easy to use the site as the app. I wouldn’t bother installing it.
Caesium image compressor is available as Windows and macOS apps, and they can be downloaded from the website. The apps are a significant improvement over the online image compressor, so they are worth installing on your computer.
For a start, any number of image files can be dragged from Explorer or Finder windows and dropped on the app to add them. I guess there is a limit, but I have not found it. It will batch compress as many files as you need in one go.
On the Compression tab on the right are sliders to set the JPG, PNG, and WebP image quality. The defaults are fine for most images destined to be used on websites, but you can change them if you want.
On the Output tab on the right are useful options, like choosing the output folder, keeping file dates, and most importantly, the image file format. JPG, PNG, and WebP formats are available (the online image compressor only supports JPG).
Click the Compress button, and it goes through the list of files and converts them. The old and new file sizes are displayed in the list. Any image in the list can be selected, and the original and compressed images are displayed. If an image is not to your liking, it could be compressed again with different settings. This is not as useful as Squoosh’s split screen for checking images, but it is better than nothing.
Conclusion
You don’t have to choose between these two image compressor tools, and the one you use depends on the circumstances. If you have one or two images that you want to optimize, Squoosh is excellent, and you can fine-tune the resulting image to get the optimum balance of size and quality.
If you have a dozen or more images that you need to compress, Caesium image compressor is much quicker. I often use the same settings for all the images, and it is often the defaults anyway, so batch processing them in Caesium saves time and effort.
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