Defishing methods with examples from 7,5mm

Discussion in 'Native Lenses' started by Jüri, Feb 11, 2014.

  1. Jüri

    Jüri Mu-43 Regular

    Dec 14, 2013
    One great thing about fisheye lenses is that the fisheye effect can be removed in post-processing, thus giving the opportunity to use these as simple UWA lenses. This was the reason I decided to aquire the 7,5mm Samyang, but after some research I've come to a conclusion that there is no perfect method for defishing photos. It's always a compromise between preserving the image and achieving a full defish. The final looks will depend on the subject and direction of perspective (or simply whether the photo was taken indoors or outside) and especially the latter plays a cruical role. So I decided to provide an overview of the looks that different methods procude. These were cropped as little as possible in order to keep the photos retangular.

    Hugin using Panini General projection (original photo on the left, resized version of Hugin produced image on the right)
    IN_Original_4-3.jpg IN_Hugin-Panini_General_10-9.jpg IN_Hugin-Panini_General_4-3.jpg
    OUT_Original_4-3.jpg OUT_Hugin-Panini_General_10-9.jpg OUT_Hugin-Panini_General_4-3.jpg

    Fisheye-Hemi plugin for Photoshop (original photo on the left)
    IN_Original_4-3.jpg IN_Fisheye-Hemi_4-3.jpg
    OUT_Original_4-3.jpg OUT_Fisheye-Hemi_4-3.jpg

    Custom lens correction in Photoshop (original photo on the left)
    IN_Original_4-3.jpg IN_Lens_correction_16-9.jpg
    OUT_Original_4-3.jpg OUT_Lens_correction_16-9.jpg
    • Like Like x 11
  2. br.davidson

    br.davidson New to Mu-43

    Jul 18, 2013
    Kent, WA
    Thanks for the comparisons. What do you mean by "almost square edge ratio?"
  3. Jüri

    Jüri Mu-43 Regular

    Dec 14, 2013
    What I actually meant was side ratio that is originally almost 1:1 when considering the image that Hugin produces, so almost a square. However, after posting the thread I realized that I wasn't completely fair to Hugin in this respect, since the image can be later rezised to 4:3. I've included the resized version to the first post. Taken this into account, Hugin applies the Panini projection a lot better that Fisheye-Hemi, but is unfortunately very ardous to use.
  4. woof

    woof Mu-43 Top Veteran

    Oct 18, 2011
    The present.
    The way you express this, it sounds as if the variable here is indoors/outdoors. If there were steps in the foreground of the indoor photos, the tools would do exactly what you see in the outdoor photos - to the steps.

    I am just trying to clarify here. Perhaps it is obvious, so forgive me if I am being... well... obvious.

    I have photos very much like this indoors... where a straight line or lines run horizontally thorugh the foreground. Hugin and Fisheye Hemi leave the foregorund lines distorted. I have not tried Photoshop, but that looks the best at straight lines in the foreground. Unfortunately, the results in the interior look a bit squat. I am arriving at a point of view that says that the tool to use for defishing is... "it depends."

    Thanks for this. Very helpful actually. Well done finding the "It depends" scenarios that demonstrate this so very well.

    Any way I can get copies of the original photos? I have another tool (PTLens) I'd like to add to this comparison.

  5. Jüri

    Jüri Mu-43 Regular

    Dec 14, 2013
    The difference is obviously not as simple as whether the photo was taken indoors or outside, but that seemed the easiest way to express the visual difference. The original files are accessible when clicking on the images.
  6. dcbrookes

    dcbrookes Mu-43 Rookie

    Sep 24, 2010
    Herefordshire, UK

    I have PT Lens which I use for de-fishing the Samyang 7.5 - I think you will find that it is basically a GUI for Panotools, so the results are likely to be the same as the Hugin ones shown by the OP (Hugin being yet another Panotools GUI).

  7. MarkRyan

    MarkRyan Instagram: @MRSallee Subscribing Member

    May 3, 2013
    Has anyone found an iOS app that does de-fishing? My photos rarely hit a computer for me to run Photoshop or Lightroom.
  8. wjiang

    wjiang Mu-43 Hall of Famer Subscribing Member

    Once corrected the 7.5mm fisheye actually covers a view wider than 7mm rectilinear, so should theoretically yield the same amount of resulting perspective distortion after removing the fisheye distortion and cropping.

    I think much of the difficulty lies in knowing how to frame the fisheye view for correction later - it's easy to compose with a WYSIWYG 7-14mm, whereas knowing what in the frame will get stretched/cropped after fisheye correction is not that easy. If the intention is to use the 7.5mm as a rectilinear UWA, one has to be able to work out what in the frame will be messed up by the distortion correction.

    I think to use a fisheye effectively one has to 'embrace the fish' to some extent. Not all shots will require correction, and some will differ in the amount and type of correction applied, as the OP has demonstrated. It just depends on what's important in the image.
  9. WhidbeyLVR

    WhidbeyLVR Mu-43 All-Pro

    Feb 14, 2014
    Whidbey Island
    I have also used hugin to defish my 7.5mm photos, with mixed success. In particular, when trying to get a rectilinear projection result there is some weird pincushion distortion which I have struggled to correct, without success. Here is an example where some of the horizontal lines appear to waver after defishing. I dunno... maybe the building was crooked?:rolleyes:

    9682739963_77368e7763_z.jpg 10064601455_00215f29b9.jpg

    I have found that using Panini for output (and purposely leaving a bit of the barrel distortion) generally hides the pincushion distortion, and often provides pleasing results. But sometimes what I really want is plain straight lines.
    • Like Like x 2
  10. wjiang

    wjiang Mu-43 Hall of Famer Subscribing Member

    Good to know, great effort btw. I think that's called moustache distortion, basically a complex mix of barrel and pin cushion. That indicates the simple(?) fisheye correction being applied doesn't use a very accurate model of the lens optics. I wonder whether something like DXO has a dedicated profile for the 7.5mm?
    • Like Like x 1
  11. Whtrbt7

    Whtrbt7 Mu-43 Veteran

    Jan 7, 2014
    Fisheye hemi is pretty good for group photos. If you're doing architectural photography, I find that doing a custom job in Photoshop seems to work really well. Just my 2 cents.
  12. WhidbeyLVR

    WhidbeyLVR Mu-43 All-Pro

    Feb 14, 2014
    Whidbey Island
    Here is a strong example of where I have found the Panini projection to work well when using Hugin. We needn't discuss the artistic merits of the subject matter in the scene.


    The balance of things in the original image is decent, but shows rather obvious fish-eye distortion. The rectilinear version is extremely distorted on the periphery and strongly deemphasizes the central figure; it is very unpleasant. The Panini projection strikes a great balance and"feels" the most like actually being there -- it is the moment as I remember it. Note the appliance in the lower right and the table/window on the left. Their proportions seem correct. Also, any problems with "mustache" distortion are well hidden in the gentle curves which remain (although they are admittedly difficult to find in the rectilinear version as well).
  13. Bl0at3r

    Bl0at3r Mu-43 Regular

    May 21, 2012
    Essex, UK
  14. Andym72

    Andym72 Mu-43 Veteran

    Mar 4, 2013
    Reading, UK
    Since every type of reprojection of a fisheye image will produce some type of distortion somewhere, which one to use for which image becomes a creative or aesthetic choice. Go with what looks right.

    The great thing about the Panini General projection in Panotools/Hugin is the slider that let's you choose a hybrid projection somewhere between Stereographic Cylindrical (the maths name for Panini) and Rectilinear.

    Sent from my iPhone using Tapatalk
  15. rparmar

    rparmar Mu-43 Top Veteran

    Jun 14, 2011
    Limerick, Ireland

    I have a batch file set up to product Panini or Rectilinear versions of my fisheye shots using Hugin. I then pick the result I like best of the three.
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