Ask Tim Grey - JPEG Options

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Today's Question: When saving a JPEG in Photoshop, at the bottom of the JPEG Options dialog there are three Format Options: Baseline (Standard), Baseline (Optimized) and Progressive. Under Progressive there is Scans, with the drop down numbers 3, 4, 5. I just noticed when saving a JPEG mine was on Progressive, and the drop down of 3. Should it be on that? I never really noticed it before....

Tim's Answer: I suppose I'd say my "short answer" to this question is that it really doesn't matter, and that you really don't need to worry about which option is set. That said, the setting you use does have an impact on the images you save in the JPEG file format, so it isn't a bad idea to understand what the options mean.

The Baseline (Standard) option is what I think of as the "normal" JPEG option. In this case, by "normal" I mean it is the JPEG format option that is most widely supported, and so it is option that has historically been supported by the widest range of software. So when in doubt, it is the safest option to choose for your JPEG images.

Of course, software has developed quite a bit over the years, and so the Baseline (Optimized) setting is now supported by the vast majority of software that supports JPEG images. In fact, in the last five years (perhaps ten years?) I've not heard from a single person who has run into a problem in terms of compatibility when it comes to JPEG images with the Baseline (Optimized) setting. And in most cases, the Baseline (Optimized) option will result in smaller file sizes compared to Baseline (Standard). Generally that reduction in file size is quite minimal, but it can be helpful for situations where you are especially concerned about file size.

The Progressive option is a variation on Baseline (Optimized). The file size will be the same as with Baseline (Optimized), but the image data is written in such a way as to have the image appear in several passes when it is opened. What that really means is that if you use a JPEG image with the Progressive option on a website, and the download speed is a little slow, the image will first appear a bit out of focus (because, for example, only every third line is displayed), then in slightly better focus, and then in normal focus. For users who have a broadband Internet connection, you might never even notice the Progressive setting was used for a particular JPEG. But it is helpful (or annoying, depending on your perspetive) for those opening images on a slow Internet connection.

I'm not a big fan of the effect you get with a Progressive JPEG image, so my preference is for Baseline (Optimized), largely because it generally reduces file size at least a little, without reducing image quality compared to the Baseline (Standard) option.

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