Before and After: Removing Distortion from a Fossil

I get my data wherever and however I can.
This time I did not recognize the distortion in the image of the ROM 55352 specimen of Rhamphorhynchus. Luckily a reader, Chris Collinson, pointed out the error and I repaired it. Rob Gay asked for before and after images. Here they are.

The original image:

Rhamphorhynchus_muensteri-ROM

Figure 1. Seems pretty obvious, now that I “see” it. This image suffers from parallax, perspective distortion. The head is too big. the tail, so far away, is too small. Notably one wing is closer and larger than the other. By matching wing phalanx lengths the perspective can be repaired.

The repaired image:

The ROM 55352 specimen of Rhamphorhynchus in situ.

Figure 2. The ROM 55352 specimen of Rhamphorhynchus in situ after perspective distortion has been removed.  Now all the proportions match other Rhamphs and the two wing phalanx sets (L & R) match. Adobe Photoshop permits one to move the corners, removing the perspective that caused the earlier problems.

The repaired image vs. an image taken from the center of the plate:

an image of the ROM Rhamph taken from the center of the plate from a greater distance

Figure 3. Thanks to Chris Collinson, an image of the ROM Rhamph taken from the center of the plate from a greater distance compared to the “repaired” image undistorted by Adobe Photoshop. The lengths of the elements are very close to one another. The wingtips diverge. The foot bones are not aligned, so perspective is less accurate, but not bad with regard to the precision required by phylogenetic analysis.

More details on the specimen appear here, including its phylogenetic nesting at the base of R. muensteri and R. gemmingi. Adobe Photoshop permits one to move the corners, removing the perspective that caused the earlier problems.

Late addition: A third image, provided today by Chris Collinson, is “multiplied” against the “repaired” image (Fig. 3). Only minor variations are noted. 

Sorry for the mistake. I’ll try not to let that happen again. Perhaps the lesson in perspective repair will be as valuable to someone out there — as it was here.

4 thoughts on “Before and After: Removing Distortion from a Fossil

  1. May I suggest one additional test – validation. I.e., get a full-frontal view of the specimen, and see how it matches with the “corrected” version. I don’t doubt that the “corrected” version is better, but we still don’t know yet how close it truly is to reality.

  2. Sorry for the morphed name, Chris. All is repaired. Thank you for the new image. The non-perspective image has been added to the “repaired” image for comparison in today’s post update.

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