ColSebastianMoran
( IRL Richard Karash )
We may stitch for increased resolution, sometimes for 35mm but especially with 120 or larger format films. Sometimes we get distortions. Those who cam-scan with film edged report wavy lines. We have all seen distortion at times, subtle shifts.
I've been exploring distortion in stitching, and I think I now have a clean test result, and it's surprising.
Conclusion: For stitching of our camera scans, best results with a good lens of minimal distortion, a lens that does NOT communicate focal length to the body, stitch in LR (Perspective) or PS (Auto). Film curvature can create similar distortion; film flatness becomes even more important when stitching. Distortion from lens or film un-flatness likely to be magnified in the stitch.
My test: started with a good digital image, then:
- Add criss-cross lines
- Slice it into four parts by cropping, stitch these back together
- Add barrel distortion to each of the four parts, stitch these
- Add pincushion distortion to each of the four parts, ditto
- Then instead of cropping, do screen grabs to make the slices.
First, the original image:
Now the stitch from four screen grabs, these have NO lens info in EXIF, comes out perfectly to my eye:
Next, the stitch in LR of the four CROPs... It's distorted. Therefore, we can conclude that LR stitch is affected by the lens info (original was shot with 24mm lens, this lens info is passed into the crops):
Now the deliberately distorted crops, first from crops with a good dose of pincushion added, then stitched:
Finally, from the same crops with a good dose of barrel distortion added, then stitched:
I've been exploring distortion in stitching, and I think I now have a clean test result, and it's surprising.
Conclusion: For stitching of our camera scans, best results with a good lens of minimal distortion, a lens that does NOT communicate focal length to the body, stitch in LR (Perspective) or PS (Auto). Film curvature can create similar distortion; film flatness becomes even more important when stitching. Distortion from lens or film un-flatness likely to be magnified in the stitch.
My test: started with a good digital image, then:
- Add criss-cross lines
- Slice it into four parts by cropping, stitch these back together
- Add barrel distortion to each of the four parts, stitch these
- Add pincushion distortion to each of the four parts, ditto
- Then instead of cropping, do screen grabs to make the slices.
First, the original image:
Now the stitch from four screen grabs, these have NO lens info in EXIF, comes out perfectly to my eye:
Next, the stitch in LR of the four CROPs... It's distorted. Therefore, we can conclude that LR stitch is affected by the lens info (original was shot with 24mm lens, this lens info is passed into the crops):
Now the deliberately distorted crops, first from crops with a good dose of pincushion added, then stitched:
Finally, from the same crops with a good dose of barrel distortion added, then stitched:
