JPEG Quality in Photoshop

Regarding the information posted in this article from petapixel.com I decided to do a quick comparison to see if there is some truth to the statements mentioned in there.


I wanted to see what the perceived quality and file size is among various JPEG quality levels when exporting images from Photoshop CS5. I know the article states that sometimes quality is affected opposite from what you might expect but I figured that it was worth a shot. There are no absolutes with many things in life and this shouldn't be any exception.


I took two basic photos. I'm using a Nikon D700, 50mm f/1.8 AI-s lens, and SB-600 flash mounted on camera in TTL. The photos were taken indoors at f/5.6 and 1/60th. The RAW came in at 2832x4256 and 15.04MB. I didn't perform any post-processing and right from Bridge I simply exported 5 JPEGs at quality levels 6, 7, 8, 10, and 12.


Here is a screenshot for Levels 6-8 with one area of detail zoomed in at 200%:

Under close inspection from my end I can actually say that the artifacts that you normally see with JPEG compression is noticeably more going from Level 6 to Level 7 and notice that the file size is nearly the same. The difference is very slight but if you look hard enough (too hard really) you can find them. Level 8 is noticeably larger, as expected, and the amount of artifacts is less.


Here's a screenshot for Levels 10 and 12 with the area of detail zoomed in at 200% again:

Artifacts? There are a few in Level 10 and I would say they are less than the previous batch. What about Level 12? I can actually see a few less again. File size? more than doubled between 10 and 12. As you can see, we are getting quite large as well.


So, what's the quick verdict on this? There seems to be some truth to the statement that when you go from Level 6 to Level 7 you may lose some quality while the file size stays about the same. So Level 6 may be the better alternative to Level 7. However if you are counting pixels perhaps bumping to Level 8 will ease you, that is unless you are trying to stay within a specific threshold for file sizes (please be conscience of mobile users!)


As far as the statements about Levels 11 and 12 being "experimental" and not really adding to overall quality. Well I can't say there is obvious evidence of this because I did notice fewer artifacts when using Level 12 vs. Level 10. The file size did more than double.


Now I know this was not very scientific and there are many types of images and variables that should come into play regarding this, however, doing a thorough scientific evaluation wasn't the point of this little experiment. All I wanted to do is find out if these statements were completely bogus or if they actually had some truth to them. A good place to start with some further research is with the Adobe Photoshop development team. They can answer the differences in the algorithms being used among all the various levels...