What is image compression? (and why your store loads slowly without it)
Image compression shrinks a photo's file size so pages open faster on mobile data, and a 5 MB phone photo is the most common culprit on small stores.
The plain meaning
Every photo is a file, and files have a size. Image compression is the process of making that file smaller while keeping the picture looking good enough for its purpose. The smaller the file, the less data a customer's phone has to download before the picture shows up.
Why a 5 MB photo is a problem
Modern phone cameras take large, detailed pictures. A single photo straight from the camera can easily be around 5 MB. That is perfect for printing a poster, but your product page is shown on a screen a few inches wide.
Picture a product page with eight photos. At 5 MB each, the page is asking a phone to fetch roughly 40 MB of images. For a shopper on patchy mobile data in a small town or on a train, that means a long wait with blank spaces where pictures should be. Many will leave before they see your product.
The same page with each photo compressed to a few hundred kilobytes asks for only a fraction of that. The shopper sees the product quickly, and your data-conscious customers do not get a nasty surprise on their plan.
Two things you can adjust
- Dimensions: how many pixels wide and tall. A phone screen does not need a 4000 pixel wide picture. Resizing to something like 1200 to 2000 pixels on the long side is usually plenty for a product page, though you should test what looks sharp for your products.
- Quality or compression level: how much detail is squeezed out. A moderate setting keeps pictures looking natural while cutting size a lot.
Our guide to resizing and compressing product images for web walks through both.
Format matters too
JPEG suits photographs, PNG suits graphics with sharp edges or transparency, and WebP often gives smaller files at similar quality. The post on JPEG vs PNG vs WebP for product images explains when to choose each.
A simple routine
- Shoot at your usual quality.
- Before uploading, resize and compress in a free app or website. Our list of free apps to edit product photos is a start.
- Batch the work. Editing one by one is slow. See how to edit product photos in bulk.
- Check each compressed picture on your phone at full screen. If edges look blocky or colours turn muddy, raise the quality a little.
- Name the files clearly, as in how to name product image files properly.
- Keep your originals in a separate folder, in case you want to reuse them later.
What I will not promise
I am not going to quote exact loading times, because they depend on your phone, network, theme and the rest of the page. What I can say plainly is that smaller image files mean less to download, and less to download is better for anyone not on fast Wi-Fi.
Quick test
Open your own store on your phone with Wi-Fi switched off and mobile data on. Browse a few product pages. If the pictures appear slowly, look at how large your original files are before uploading. Fixing images is one of the cheapest improvements a small store can make, since it needs no new tools and no money, only ten minutes before each upload.