When you save your images as JPEG's after editing, then you will have noticed that you have an option when you save the file to choose a quality level - if you are like me, this might have stumped you for a little while! After a little bit of research, I am pleased to pass on all that I have learnt regarding JPEG compression! (Geek!!)
Anyhoo, the number options basically says how much compression your image will get, and therefore it makes sense to choose this wisely! I'm going to tell you which level I save at, and why, but before we get to that, I'll just briefly explain what compression is and why we worry about it in case anyone wonders what I'm talking about!
What is Compression?
A good way to think about JPEG compression is to imagine you are putting your print into an envelope. If you put it into the same size envelope as your print, you have not squashed the image down at all, so that when you take it out at the other end, it is as good as new. But to save on space, you might want to put that print into a smaller envelope, compressing it so it fits into this smaller space. As the print is larger than the envelope, you are going to need to fold it in half, or even smaller , depending on just how small your chosen envelope is. This time, when you take the print out there will some degradation or marking - all that folding and making it smaller reduced the quality of the print. The smaller the envelope, the more folding and squashing we do, so the more degradation of the final image we get. It's exactly the same principle with compressing images - we are trying to take large prints and make them fit into smaller envelopes :)
The Different Levels Of Compression
You have different levels of compression - Photoshop runs from 1 - 12, and in Lightroom 1 - 100. (I'll just talk about 1 - 12 here, but the same principle applies to the Lightroom numbers) 1 is obviously the lowest quality, with the most compression (the smallest envelope) and 12 is the highest quality with the least compression (largest envelope!)
At this point, you will probably think what I used to think, and that is to use the highest quality setting available - 12 - as that way you don't have to worry about compression and what it's doing to your image. Yippee! But there is one small problem, and that is the file sizes - they are flippin' HUGE! Just to give you an idea, one image saved at level 12 was a whopping 16.5 MB, and other was 8.1 MB, so not exactly tiny. Obviously this takes up a lot of space on your hard drive, makes it harder to share, and longer to back up. So, making JPEG's of a smaller file size would be beneficial.
Stop! You Don't Need to Save at The Highest Level!
The good news is, you don't really need to use Quality 11 or 12 when saving your images as JPEG's for print, as there is actually no perceivable difference in print quality between a Level 10 or Level 12 saved JPEG. To give you an idea of the difference in file sizes between the two: that image saved as Level 12 JPEG was 16.5MB, but the exact same image saved at level 10 was only 6.2 MB. That is an extreme example, but another image was 8.1 MB at Level 12 and only 2.7 MB at Level 10. That's a huge difference in file size for no / negligible difference in quality.
What I Save At
Therefore, the highest level I save my JPEG's is Level 10. But I will only save at this level if I am intending to make a large print or canvas - I want to make sure that I have the best quality going to the printers (as a side note, most printers will ask for 10) However, I have been assured that 9 is more than enough - I just like to make sure!
However, as 95% of my images are destined to become part of my yearly photo books, with most printed at 4 x 6 sizes within the pages of the book (the absolute largest being a full page print at 12 x 12) I really don't need the highest quality level for this - so for this I use Level 9. This is the level I use for all my JPEG's and the size that I back up to SmugMug. I'm happy with that level overall - it's more than enough for a good size print or canvas should I lose everything else (I keep my PSD files too) and it's small enough to not take up too much space on my hard drive and upload offsite easily.
We all have different workflows and end outputs for our photos, so this isn't to tell you what you should save as, but something you can consider based on your own requirements. If you are saving one JPEG copy only and you want to make sure it is the highest quality available for archival purposes, then use 11 or 12. If you are printing large, go for 9 or 10. Smaller? Then 8 or 9 will be fine. Lower than that and you are getting into more heavy compression, so should only be used for "throwaway" files.
However, don't save as a low quality level simply to save on disk space - you want to make sure your prints look the best the can be, and if these are your only copy that you preserve them as best you can, so consider the quality setting you need for both the final output and storage.
Hope this helps anyone else struggling with huge file sizes!