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Any Auto lens correction experts out there?

Discussion in 'Image Processing' started by GBarrington, Jul 29, 2016.

  1. GBarrington

    GBarrington Mu-43 Veteran

    On a different forum, I've been helping a trial user with some lens correction issues in ACDSee U9. And the questions are getting to go beyond my level of knowledge and understanding. I hope someone can help.

    I don't think you need to be an expert with ACDSee to answer since this is more about the profiling process than it is ACDSee (ACDSee uses the lensfun database).

    I described how one can create a sort of "Pseudo" lens profile with ACDSee for an unprofiled lens by using a different lens that has been profiled and making it the default for the unprofiled lens. (presumably the user tries various combinations and selects the one closest to the desired result before creating that pseudo profile)

    But this new user asked if it is possible to use a profile for the correct lens from a different camera and pasting it into the lens profile file for the camera you want. Since these are XML text files, it should work, physically at least, but is this going to offer results any better than the provided 'pseudo profile' methodology?

    As I understand the process, a lens profile is created for a specific lens and camera body combination. But if you pull a profile from, say, a Canon FF DSLR and try to apply it to a Sony, Olympus or even a Nikon FF camera, will the results be any more accurate than selecting a lens already tested for your camera and creating a pseudo profile from it? Certainly the CA correction would be off! My thinking is there are minor variations in sensor size and (possibly?) how the sensor is implemented in camera that might cause a variation in correction quality.

    I guess what I'm asking is:

    Which method of trying to provide auto correction for an unprofiled camera lens will get you to the most accurate results (or maybe the least wrong results!)
     
    Last edited: Jul 29, 2016
  2. robcee

    robcee Mu-43 Veteran

    289
    Jan 10, 2016
    Toronto
    Rob Campbell
    um, you're doing it wrong.

    Olympus and Panasonic m43 cameras embed the lens corrections in the file. What comes out of the cameras is already corrected to some degree based on the lens profiles stored in the lenses.

    Applying lens corrections on top of that from different camera bodies and lenses will apply whatever distortions were measured for that lens/body combination to your image. That'll further reduce detail in the corners and probably warp your image, overcorrect chromatic aberrations and generally make a mess of things.

    DxO Optics do a good job with the m43 cameras because they actually measure the bodies and lenses themselves and come up with correct profiles.

    What are you hoping to achieve with this?
     
  3. barry13

    barry13 Super Moderator; Photon Wrangler

    Mar 7, 2014
    Southern California
    Barry
    Are we talking RAW or JPEG?
    JPEGs will be corrected in-camera.
    RAW will not, but the info will be embedded and SOME RAW processors may automatically apply it.

    I use RawTherapee, and the 'auto' distortion correction normally has a noticeable effect at the wide end of my 12-40mm, but it doesn't do anything at longer FLs.

    CA correction is more manual in RT.
     
  4. SVQuant

    SVQuant Mu-43 Top Veteran

    851
    Sep 20, 2015
    SF Bay Area, California, USA
    Sameer
    ACDsee Pro 9 seems to do a good job of applying distortion corrections, though it is not clear to me that it uses the embedded information in the RAW files. I believe that it uses the lensfun database, but I don't know how frequently the data is updated.

    I think that the OP may be looking to apply lens profiles for adapted lenses. My preference would be to use a body which has a similar-sized sensor if available for the particular lens. I think that using a FF based profile may not work so well for smaller sensors. In fact, the lensfun FAQ states:

    My lens should be supported but the camera is missing. What can I do?

    The camera entry in the database only holds crop factor and lens mount. As a workaround you can simply select any other camera with the same lens mount and sensor size or crop factor.​

    @GBarrington@GBarrington
    I just realized that your overview of ACDsee 9 really helped when I was evaluating it a few months ago. Thanks.
     
  5. GBarrington

    GBarrington Mu-43 Veteran

    No i'm not, ACDSee has chosen to implement the Lensfun Database. That is no less correct than using the embedded correction data that the m43s cameras offer. And in fact, relying solely on that embedded data means that one is unable to apply auto lens correction to legacy lenses. There are many good reasons to not use the embedded data.

    DXO does a nice job with lens correction, but I like ACDSee better in every other way.

    Also, ACDSee experimented with the embedded data and abandoned that methodology. See my blog article here.

    What I want to achieve is to figure out a way to get some sort of auto correction while I am waiting for the newly created profiles to get sent to Lensfun, pass whatever review that LensFun applies, and ACDSee applies the new lensfun database. But mostly, I want to answer a newbie user's questions.