Question for raw shooters re: lens distortion correction

Started Mar 31, 2010 | Discussions
Dennis
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Question for raw shooters re: lens distortion correction
Mar 31, 2010

The lens tests I saw on photozone.de show that the otherwise excellent Panasonic lenses (the 20 & the kit zoom in particular) show significant distortions if not corrected. The camera-generated jpegs looked great; raw files processed by converters that don't autocorrect show the distortion.

My question is: how do you deal with this ?

In particular, any Lightroom users who have found a convenient solution that fits their workflow ?

I've been holding off on buying an EVIL kit until I see what Sony offers since micro 4/3 isn't totally compelling to me just yet (I like this feature from this camera, that feature from that one, certain lenses, while others are missing).

But during all the waiting, the potential 'problem' of not having auto lens correction struck me as a downside.

Thanks,

  • Dennis

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sacundim
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Not a problem at all if you use Lightroom
In reply to Dennis, Mar 31, 2010

Dennis wrote:

The lens tests I saw on photozone.de show that the otherwise excellent Panasonic lenses (the 20 & the kit zoom in particular) show significant distortions if not corrected. The camera-generated jpegs looked great; raw files processed by converters that don't autocorrect show the distortion.

My question is: how do you deal with this ? In particular, any Lightroom users who have found a convenient solution that fits their workflow ?

Lightroom performs the corrections transparently and automatically. It doesn't affect your workflow at all.

I've been holding off on buying an EVIL kit until I see what Sony offers since micro 4/3 isn't totally compelling to me just yet (I like this feature from this camera, that feature from that one, certain lenses, while others are missing).

But during all the waiting, the potential 'problem' of not having auto lens correction struck me as a downside.

It means you have less choice today when it comes to RAW converters. That might become better in the future, when more makers adopt software corrections and the RAW converters add in support for that.

But if your RAW workflow application is Lightroom, it's just not a problem.

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Godfrey
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Re: Question for raw shooters re: lens distortion correction
In reply to Dennis, Mar 31, 2010

Adobe applies all the lens corrections that either Panasonic or Olympus lenses and bodies inject into the raw files from the lens' firmware with both the Camera Raw plugin and Lightroom. There is no issue if these are your raw processing tools.
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Dennis
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Re: Not a problem at all if you use Lightroom
In reply to sacundim, Mar 31, 2010

Wow - waddya know, a search would have turned that up I honestly didn't think to search for it because Lightroom doesn't have manual lens corrections that I can use now ! (Too bad, too).

Thanks, that's very reassuring !

  • Dennis

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saghost
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Re: Question for raw shooters re: lens distortion correction
In reply to Dennis, Mar 31, 2010

I believe the only RAW converters that do not automatically correct distortion are the ones based on the open source DCRaw engine. Everything else corrects automatically, as the system was designed to. I don't consider it to be a limitation - though if you happen to use a DCRaw based system, it could be a rude shock.
Walter

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Dennis
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OT, but how ?
In reply to saghost, Mar 31, 2010

For you, Godfrey or anyone else ... just curiosity at work now.

Do Oly/Panasonic supply specs for distortion correction ? Lightroom doesn't have support for lens correction outside of this that I know of (certainly no manual sliders that I can use with my current images).

Did each converter author have to write distortion correction routines (presumably with input to help map metadata) ? Or is it possible that the micro 4/3 consortium (such as it is) actually supplied code ?

Thanks to all,

  • Dennis

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StillHaveMyDiana
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Future lenses?
In reply to Godfrey, Mar 31, 2010

This type of lens design approach is a no-brainer for the future, as certain types of distortions are very easy to correct in SW vs. lens shape and vice-versa. It will be interesting to see if the manufacturers agree on a common meta-file format for lens correction data.

The next step is presumably real-time feedback of distortion information from the sensor back to the lens, as is used in astronomical telescopes.

Interestingly, these advances may first occur in cellphones, where the manufacturers want super-cheap plastic lenses with "decent" wide-DR, zooming video MP images, and have a powerful processor on-board to do the math.

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sacundim
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Re: OT, but how ?
In reply to Dennis, Mar 31, 2010

Dennis wrote:

Do Oly/Panasonic supply specs for distortion correction ? Lightroom doesn't have support for lens correction outside of this that I know of (certainly no manual sliders that I can use with my current images).

They must have supplied specs to at least Adobe, and presumably Apple. I don't know that they supply specs to everybody.

Did each converter author have to write distortion correction routines (presumably with input to help map metadata) ? Or is it possible that the micro 4/3 consortium (such as it is) actually supplied code ?

I don't really know, but just from being a software engineer, I'd assume the former even if the consortium supplied example code.

One interesting point, however, is that the newest version of the Adobe DNG file format (1.3.0) has support for lens correction metadata, which is documented in the specification (starting at page 72, ending at the top of page 77):

http://www.adobe.com/products/dng/pdfs/dng_spec_1_3_0_0.pdf

This contains a description of two distinct image transformations that are used to correct the distortion in the raw sensor data. So, basically, the mathematical and algorithmic part of how to correct the images is public knowledge by now; what's not public knowledge is how the Panasonic and Olympus RAW file formats encode the correction parameters. But it sure looks like if one could reverse-engineer the latter fairly easily if one had a few vendor RAW files paired with an Adobe DNG conversion of the same files. It just doesn't look like anybody's rushing to do so, however.

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sean000
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Re: OT, but how ?
In reply to Dennis, Mar 31, 2010

Dennis wrote:

For you, Godfrey or anyone else ... just curiosity at work now.

Do Oly/Panasonic supply specs for distortion correction ? Lightroom doesn't have support for lens correction outside of this that I know of (certainly no manual sliders that I can use with my current images).

What version of Lightroom do you use? I though Lightroom and Photoshop had pretty much the same capabilities when it comes to RAW conversion. I'm using Photoshop CS4 with Adobe Camera RAW 5.6 and there are sliders for correcting barrel/pincushion distortion, vignetting, chromatic aberrations, etc.

As far as automatic distortion correction: I would imagine that the RAW converter would already need to have the functionality to correct distortion built in, and then Oly/Panasonic would just provide the amount of correction required for each lens as part of the Software Development Kit they provide to companies like Adobe.

Did each converter author have to write distortion correction routines (presumably with input to help map metadata) ? Or is it possible that the micro 4/3 consortium (such as it is) actually supplied code ?

Thanks to all,

  • Dennis

I bet the information is supplied by the manufacturer as part of the same SDK that tells them how to read the proprietary RAW data and metadata.

I like this trick in that it can provide smaller lenses that appear to deliver nearly flawless results. With my Nikon DSLR lenses some of them have more distortion than others, and I correct that distortion manually when it bothers me (it isn't that noticeable in every photo). On the other hand, if you ever use these lenses on future cameras that don't support the autocorrect feature, or if you use RAW converters that do not support the autocorrect feature, these m4/3 lenses won't look as good as they once did. That said the distortion on the 20mm is not too bad. It's much worse at 14mm on the 14-45mm.

Sean

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haunma
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Re: OT, but how ?
In reply to sacundim, Mar 31, 2010

sacundim wrote:

One interesting point, however, is that the newest version of the Adobe DNG file format (1.3.0) has support for lens correction metadata, which is documented in the specification (starting at page 72, ending at the top of page 77):

http://www.adobe.com/products/dng/pdfs/dng_spec_1_3_0_0.pdf

This contains a description of two distinct image transformations that are used to correct the distortion in the raw sensor data. So, basically, the mathematical and algorithmic part of how to correct the images is public knowledge by now; what's not public knowledge is how the Panasonic and Olympus RAW file formats encode the correction parameters. But it sure looks like if one could reverse-engineer the latter fairly easily if one had a few vendor RAW files paired with an Adobe DNG conversion of the same files. It just doesn't look like anybody's rushing to do so, however.

Are we sure the spec isn't publically available? I've been critical of that in the past, but I don't know if anyone has tried to obtain it without an NDA or license fees. (Where would you start? It's almost impossible to find an engineering point of contact nowadays in a large corporation.)

DCRAW can perform a simple correction for lateral chromatic aberration, prior to demosaicing. It would be nice if I could write a script to extract the chromatic aberration terms from the RAW file and provide them on the DCRAW command line. For prime lenses it isn't hard to derive these experimentally, but I could see it being a pain with a zoom.

Post-raw-conversion, there are good alternatives; see for example

http://wiki.panotools.org/Tca_correct

What I don't know is to what degree the demosaicing is compromised by lens aberrations, if you wait until after raw conversion to correct them.

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Dennis
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Re: OT, but how ?
In reply to sean000, Mar 31, 2010

sean000 wrote:

What version of Lightroom do you use?

I'm using 2.5 - haven't donethe 2.6 upgrade yet as it doesn't appear to offer anything I need. I also have 3.0b2 and neither of them show any lens distortion corrections. Lens Correction has vignetting and CA only.

As far as automatic distortion correction: I would imagine that the RAW converter would already need to have the functionality to correct distortion built in, and then Oly/Panasonic would just provide the amount of correction required for each lens as part of the Software Development Kit they provide to companies like Adobe.

That's what I would have guessed which is why I falsely assumed that LR did not support the micro 4/3 auto corrections.

Thanks again to everyone,

  • Dennis

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klopus
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Heres' an example
In reply to saghost, Mar 31, 2010

saghost wrote:

I believe the only RAW converters that do not automatically correct distortion are the ones based on the open source DCRaw engine.

Yes, major paid converters like newest ACR & Lightroom and Sylkipix do corrections. Not sure about DxO, Phase One and Bibble though. Free and excellent RawTherapee doesn't support it though it's demosaicing and processing engine isn't based on DCRaw. Same with Lightzone that i love dearly which uses DCRaw only to decode files, not to process them

Everything else corrects automatically, as the system was designed to. I don't consider it to be a limitation - though if you happen to use a DCRaw based system, it could be a rude shock.

And I consider it's a big limitation since my long-time workflow and DAM is based around ACDSee Pro and it doesn't do corrections. I'm not in the mood of paying for LR (which i don't like in a 1st place) and converting tags and titles for thousands of images. For now I hooked ACR into ACDSee but is slows and complicates workflow considerably. Anything that limits consumer choice by imposing extra requirements on 3rd party software is bad.

Btw, here's an example:

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Godfrey
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Re: OT, but how ?
In reply to Dennis, Mar 31, 2010

Dennis wrote:

What version of Lightroom do you use?

I'm using 2.5 - haven't donethe 2.6 upgrade yet as it doesn't appear to offer anything I need. I also have 3.0b2 and neither of them show any lens distortion corrections. Lens Correction has vignetting and CA only.

LR v2.6 updated a number of problems, some of them serious bugs that crept in with v2.5 (and for Apple PowerPC systems particularly!). It's also the first version of Lightroom that extracts the LensID information from Panasonic JPEG and RW2 files that contain it and shows it in the metadata section of the Library module.

The Micro-FourThirds lens corrections are handled automatically, there are no controls for it. The raw conversion engine reads the parameters from the raw files' metadata, which are supplied by the lens to the body, and applies the corrections to produce the intent of the lens manufacturer.

The parameters for these correction operations are documented for DNG v1.3 now. They are standard for Micro-FourThirds so Panasonic and Olympus had to have shared them with Adobe.

To date, Panasonic supplies both geometric and chromatic aberration corrections in their mFT lenses and transfers both to the .RW2 files. Olympus lenses only supply geometric corrections, regardless of what make body they're used on, and Olympus bodies only read the geometric corrections regardless of lens fitted and inject just those into the .ORF files.

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Godfrey
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I have a few seats available still for my April workshop:
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This will be held in Palo Alto, California.
Contact me for more information

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