Sure you want JPG?
JPG is the format to use for photos when you want to keep file size* small, like when you’re posting photos on the Internet. But if file size isn’t an issue—if you’re exporting a master file that will be saved on your computer, for example—use a non-lossy file format like TIF or PNG. And for shooting digital photographs, I strongly recommend the RAW format if your camera supports it.
*Note: by “file size” I don’t mean pixel dimensions—how big the photo will appear on a screen—I’m referring to the amount of disk space the image file occupies.
Yes, I want JPG.
Then you’ll want to find the sweet spot, where you strike the best balance between small file size and high image quality. Of course you want your photographs to look as pristine as possible, but if you have a lot of photos on a website, you don’t want to lose people who have slow Internet connections. Also, your search engine ranking can suffer from a site that’s slow to load; you can use Google’s free PageSpeed Tools to check your site’s speed, and get recommendations for improving it.
So which quality setting should you use? It depends. A few things to keep in mind:
- Some photos can handle a lot of compression before showing degradation, while others will show loss of quality with only a small amount. Images with a lot of blue sky, for example, tend to need higher quality settings to avoid posterization (abrupt changes in tone rather than smooth gradations), while an image with a lot of detail and texture might look completely fine with a much lower quality setting.
- Although the Lightroom JPG quality slider goes from 0 to 100, it’s actually only a thirteen step scale, according to Jeffrey Friedl, a computer programmer and creator of many very useful Lightroom plugins. According to Friedl, “Lightroom maps the 101 points in its 0-100 quality scale to only 13 different quality outputs. Setting the Lightroom quality to 70, for example, results in the exact same output as setting it to 76, or anything in between. 7 is the same as zero, and 93 is the same as 100.“
- Do your own tests. Although I’ve been using Lightroom for years, and have exported many thousands of JPGs, I was surprised to find—after I did a few tests—that I could get away with lower quality settings than I previously would have thought, which is good news; I can keep my file sizes smaller, which means a faster-loading site.
Friedl has an excellent Lightroom plugin for this, called the Jpeg Export Quality Tester, which makes it super fast and easy to export JPGs at all 13 different quality settings. If you don’t use that, of course you can just manually export copies of the same image at different quality settings. Either way, it’s a worthwile experiment to try at least once.
- Some websites compress your image files during upload. If your exported JPG looks great on your computer, and not so good once you’ve upload it to a website, that may be because some sites apply lossy compression during the upload process. Facebook is known for severely compressing image files, which can result in obvious degradation. Photoshelter has suggestions on improving Facebook image quality. Wordpress sites also compress image files during upload, though not as heavily as Facebook. Wpmudev has instructions on how to disable or change WordPress compression settings.
JPG Test example
Here’s a test I conducted using the previously mentioned Jpeg Export Quality Tester plugin. In Lightroom, I selected a RAW photo (your source file should be the highest quality version of the photo you want to run the test with), then went to File: Plug-in Extras: and selected “Launch Export Quality Tests.” The plugin does the rest: exports JPGs at all 13 quality settings (as well as a non-lossy TIF version), creates a folder for them as a Lightroom collection, and displays a graph showing how much file size reduction you get at each setting.
The above photo has the lowest quality setting, “0-7.” You can clearly see boxy artifacts in the leaves, especially the ones in the foreground. Way too much compression for me.
The image on the left was compressed at the “47-53” quality setting; the image on the right has no compression. If you examine these two images closely you’ll see that the non-compressed image looks better—the gradations a bit smoother for example—but in my opinion it’s a very subtle difference. And looking at the graph below (generated by the plugin), you can see that the image on the left has a file size that’s only 85kb, compared to the highest quality setting which results in a 372kb JPG file, and the TIF version (not shown on the graph) is 762kb.
I would recommend running a few tests yourself, with different types of images: maybe a landscape, a close-up portrait, then something with a lot of texture.
JPG is the best file format for photos when you need to keep the file size small, but there are better formats to use when small file size isn’t a priority. The ideal amount of compression can be determined by comparing exported files from the same photo with different quality settings. Some images can handle more compression/lower quality settings than others, depending on what the photo looks like.