October 31st, 2012, 11:57 PM
Software-Corrected Barrel Distortion Revisted: Sony RX100
We were the first to break the story about marked software-corrected barrel distortion with the Panasonic LX3, and since that time just about every small camera manufacturer has followed in Panasonic's footsteps. Using software to correct barrel distortion allows camera manufacturers to build fast lenses which are smaller and less expensive than they would be if optically corrected for distortion.
Like other compact zoom cameras with fast lenses, the Sony RX100 has a lens which suffers from pretty severe barrel distortion which is then corrected by the camera. The leading RAW processing software Adobe Lightroom not only applies the same barrel distortion correction as the in-camera JPEG engine - it does so without any option to disable the distortion correction.
The animated GIF below shows a resized version of the same RAW file processed in Adobe Lightroom (no barrel distortion) and Capture One 7 (barrel distortion left intact). As you can see, the distortion correction involves stretching out the edges and corners of the frame. The price to pay is a distinct loss of image sharpness at the edges/corners of the image.
The default noise reduction and sharpening levels differ between Lightroom (LR) and Capture One (C1), so I tried to process them for reasonably similar center sharpness and noise.
100% center crop:
As soon as you move out to the right edge, the relative sharpness of the two files begins to vary significantly:
In the upper and lower right corners, respectively, the differences in sharpness are even more apparent:
As you can see from the examples above, much of the reported edge softness of the RX100 lens is attributable to the effects of barrel distortion correction. The corner performance of the uncorrected lens is very decent. Moreover, LR seems to sacrifice more detail than necessary in the process of distortion correction. I can get better results processing with distortion intact and then correcting the distortion in a separate step in Photoshop.
Many lenses which have less than optimal edge sharpness are much sharper without the mandatory corrections imposed by LR. The Panasonic 14mm f/2.5 Micro 4/3 pancake is such a lens, as are most Micro 4/3 wide angle lenses. For years I've been asking Adobe to turn on distortion correction by default by give us an option to disable it for those occasions where we can live with the distortion in order to gain either angle of view or edge sharpness. For the time being, I'll look to C1 when that need arises.
A free trial of C1 Pro can be downloaded here.
November 1st, 2012, 06:50 AM
software correction should ALWAYS be able to be turned off. I think people who would use advanced features like that know what they are doing. Nice write-up Amin. The pixel peepers thank you.
November 1st, 2012, 08:35 AM
Thanks Amin. I know that now you have an RX100, we're going to learn a lot more about how the camera works! It's already become a main camera for me -- will be interested in hearing how it fits into your bag.
It does show (continues to show) Sony's marvelous engineers. That's a nice lens packed in there! The softness is understandable when stretched (with the level of softness being the debatable part).
For Halloween last night, I tried taking shots of my daughters and their friends with my 5D + 85/1.8 before they headed out. Not the right camera/lens (I don't have anything shorter than 85mm, and the light was too low for that focal length, so the pics were a bit blurred). Grabbed by 5n. Still not quite right (using legacy lenses, had to stop down a bit to get sharpness, then I again lost the light I needed). Ah. The RX100 did exactly what I needed. Fast aperture at wide angle and clean high ISO anyway, and all the girls were in focus from the inherent deep DOF. I love my RX100!
November 1st, 2012, 09:29 AM
Interesting thread. I know that there is/has been lots of noise in regards to mFT lens corrections. I believe there are a couple of sites( I think lenstip) that really slam some of the more expensive mFT primes and zooms because they don't look at the corrected output. Obviously something is sacrificed when fixing distortion. Looking at the uncorrected files, the edges don't look that bad. However, I don't think the panny 14mm looks that bad after correction though. I know I'm comparing a prime to a zoom lens. I know the corrected output for the Olympus MkII zoom kit lens doesn't look this bad either. So, is it that the native distortion is just that bad, or is it that Sony/lightroom's correction algorithms are not very good?
I've really thought about picking up this camera as strictly a nighttime/low light replacement for my mFT. Its smaller and has more flexibility than a panny 20mm stuck on a mFT. The lens decentering obviously still bothers me some.
The more I think about it, I still am amazed at the lens quality of the XZ-1 wide open at 28mm. But wait, maybe olympus can take that design, scale it up, and slap it in front of the RX100 sensor now that they are both in cahoots. I'd pay 800 dollars for such a marvel.
November 1st, 2012, 10:06 AM
Few things: 1) The Olympus and Panasonic lenses you mentioned have better edge performance than this Sony lens, so they hold up better after distortion correction; 2) The Sony has more megapixels, which gives a false penalty when viewing at 100%; 3) Lightroom doesn't seem to have a great correction algorithm. I get better results using distortion correction in PTLens or C1.
Originally Posted by Djarum
November 1st, 2012, 10:20 AM
Amin, did you test Sony jpg distortion correction vs. LR distortion correction on RAW for the RX100? Of course, I could test this myself, but I thought I'd ask first :)
November 1st, 2012, 10:29 AM
Two questions. First, are there any raw converters for macs that don't auto correct, or at least give the option not to?
Secondly, has anyone compared the Nex 7 with 16mm 2.8 with and without auto distortion, and does the 16 give better corner sharpness when uncorrected?
November 1st, 2012, 10:53 AM
Haven't tried that. I have a somewhat serious allergy to in-camera JPEGs - hives, tongue swelling...
Originally Posted by wt21
C1 is Mac/Windows and gives the option to disable distortion correction. There is a free 60 day trial which I linked in the first post. Raw Developer is Mac only and doesn't do distortion correction. Terrific app.
Originally Posted by Alan Brown
I haven't tried NEX 7 with 16/2.8, but my understanding is that the 16 has little distortion to begin with.
November 1st, 2012, 10:55 AM
You're a doctor. Can't you take something for that :p
Originally Posted by Amin Sabet
November 1st, 2012, 11:52 AM
off-topic, but I never knew that. Somehow it makes perfect sense though, I guess your online appearance is still one of a doctory type
Originally Posted by wt21
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