DxO autocorrection wide-angle stretching??

Started 6 months ago | Discussions thread
tokumeino Contributing Member • Posts: 960
It is not about softwares, but about geometry

Giiba wrote:

tokumeino wrote:

I'm afraid that this looks very conventional. Actually Fish->Recti is just a geometrical transformation and there are not many ways to perform it. DxO is just like other tooles here. There are different tranformations like the very popular Panini for instance, but it does not produce rectilinear images.

Here, the side borders look to be streched by a x3 magnitude (approx), and much more for the side corners. It is not a critism at all wrt DxO. It is actually the only way to do and even the fabulous DxO cannot make parallel lines joining

You're right there is now way to completely remove the stretching. For me the piint is more I did the above in 30 seconds. I used the built in distortion profile for the 8/1.8, then used the viewpoint perspective tool to straighten out the crib sides (as the crib wasn't perfectly centred and straight on).

The DXO suite just makes this so easy. Something like Fisheye Hemi does better at keeping the corners looking natural, but used on this shot it still leaves things looking wonky due to the imperfect perspective. For use of this photo I then cropped the shot to include just the crib and remove the corners, giving me a unique photo to share my news with friends.

Most of the time I crop my defished shots to 16:9 which also fixes the corner issue.

Sorry if I don't understand but...

Fisheye Hemi typically performs a Panini projection. There are many ways to project a 3D object on a plane (which is what photography does). Very roughly, and among other projections, you have :

  • Rectilinear preserves straight lines but not the distance between points (and thus you get distortion)
  • Fisheye preserves distance between objects but not straight lines (less distortion but curved lines - except diagonals)
  • Panini preserves lines when they are vertical (but not horizontal), and preserves distances better (especially on the horizontal axis). This is typically what Hemi does.

To experiment this, I would recommend Hugin, which offers many types of projection. Nice results and you learn a lot by using such a software.

The profiles built in regular softwares (DxO, LR, C1P etc) all perform Recti projections : with a picture, they try to make lines straight. And to do so, there is no miracle : the geometrical projection will always be the same. If you want to avoid distortion, you need an alternative projection and a dedicated software.

The point is : you cannot preserve at the same time :

  • straight vertical and/or horizontal lines
  • distances between objects

It is not about softwares, just about geometry. Recti is recti : whatever the software, you'll always get the same distortion. If you want to reduce distortion, then you need another projection.

PS : this has been studied in painting way before photography. For instance, the Panini projection is from the 18th century (any photographer should study painting first ):

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