Anyone use the auto distortion control on Nikon

[greg14]

In the shooting menu, Page 205 of the Nikon D7000.
It has a Auto Distortion Control function ?

Not sure if other Nikon or Canon has the feature BUT :
Does anyone use it 0n/off ?

There is also one in the retouch menu mode.
I never use the camera to retouch or change a photo.
I only do that with computer software.
Thanks,
Greg

[Dave Humphries]

Hi Greg,

I have that feature on my D5000 - it sounds like a good idea, so I leave it on.

It says (on p150 in D5000 manual), it only works on Nikon G or D series lenses, which is understandable.
Since the G series is all I use, I may as well have the benefit.

It says it helps control barrel/pincushion distortion and since I don't think I have ever had to correct that in PP, I guess it must be working.

I never retouch in camera either.

Cheers,

[tclune]

I played a bit with the auto distortion control in Capture NX2, which I understand is the same as Nikon uses in its cameras. Here is a photo made with the Nikon 35 mm f/1.8 that I saved both with and without auto-correction (this one is with auto correction):



I then differenced the two images and saved that as a photo:



The correction algorithm used appears quite strange to me. My guess, based on the circular correction applied, is that DXO would do a better job. But that is based on nothing other than my shock at the Nikon correction. FWIW.

[greg14]

As to the two pictures, I do not think you are talking about the same item.

You, I believe are talking about the auto correction that changes items, such as exposure and color balance and edge sharping.

The Auto feature I am talking about is strictly about distortion, and is called Auto Distortion Control.

Greg

[tclune]

No, that is exactly what I am talking about. The 35mm f/1.8 has some barrel distortion, and enabling the auto distortion correction straightened, e.g., the spires on the side of the altar. I cranked up the gain to show the difference between the corrected and uncorrected images. What surprised me is that they appear to use an algorithm that limits the displacement of pixels, so they have an oval of "fixed pixels," and shift the pixels inside or outside it presumably in opposite directions (although the absolute value of difference in pixels doesn't capture that info.)

What you would expect generally in this kind of differencing is something like an edge detection filter. That is pretty much what you get . A classic edge detection routine shifts an image a bit and subtracts the shifted image from the unshifted one. The only thing that survives to any degree is the information about where the edges are -- the rest of an image's pixels are pretty much the same as their neighboring pixels.

Now, if you correct for barrel distortion, you should have a resulting image that is very much like a shifted image. The subtraction should show you in edge outline the shape of the lens distortion. If you have ever seen, e.g., the graphs in Photozone's lens reviews of a lens' distortion, you know pretty much what I would have expected to see -- an outline of a barrel-distorted image. Instead, I see an oval of no difference with differences inside and outside. This shows directly the kind of algorithm that Nikon is using, and it was a surprise to me. HTH

[greg14]

Question :

Did you shoot the Church Picture in Raw ?

The reason I ask is that on a another photo forum (sorry) there is a discussion that the feature does not work in Raw.

Any thoughts on Raw v jPeg ?

[tclune]

Yes, I shot it in raw. I applied the auto distortion correction in Capture NX2. I saved one JPEG of the image without Auto Distortion Correction enabled, then enabled it and save another JPEG. I then diff'ed the images in another image processing package. The difference image I show demostrates that it does, indeed, work this way (otherwise the difference image would be all black.) The camera doesn't apply the correction algorithm to raw data, but Capture NX2 applies the same algorithm AIUI to the data in software. I trust that is clear.