The Culprit....Identified!

In my last post, I spoke about using Lightroom’s ‘Photo Merge’ in the combined HDR/Panorama mode and noted that it seemed to cause a ‘smear artifact’ (as seen below). I also mentioned that the source of this could be user error or some other unknown problem and that I would be investigating further. And with investigating, I have identified the culprit!

Note the ‘smear’ artifact in the bricks just above where the arches come together.

The problem was neither user error nor Lightroom’s HDR/Pano merge capabilities (at least it wasn’t the primary reason). As it turns out, the image resulting from the Lightroom HDR/Pano merge was quite noisy and the artifact I note above was actually generated in Topaz’s Photo AI (the same happened with DeNoise AI as well) during the noise removal process. It hadn’t been immediately apparent to me since I had merged the baseline layer with the noise removal layer. I only noticed the problem after that merge and therefore erroneously concluded that it had come out of Lightroom that way.

Though I was unable to use the image without noise removal (yes, it was that noisy), I was also unable to find any of my noise removal software that could do a better job. Instead, I decided that for the majority of the image I could just use the middle exposures from the HDR/Panorama series and stitch them in Lightroom’s Photo Merge Panorama mode. I could then just mask in the windows from an underexposed image from the HDR series to try to preserve window detail, as that was really the only very bright light source. And this method was successful, as can be seen below.

Cathedral of Learning © Howard Grill

Here, at a 100% view, is the part of the image that was filled with the ‘smear artifact’ on the prior version. One can see that the artifact is no longer present when the noise removal step is eliminated. The color is slightly different than in the prior version because I reprocessed it from scratch.

Note that the ‘smear’ artifact is no longer present.

Of course, the question remains, why did the Lightroom merge produce such a noisy finished image given the wide exposure range ‘fed’ to it with the HDR series? Of that I am not sure. I will need to do some more experimenting with the HDR/Pano merge to see if this is an ongoing problem in my hands. Hopefully it was a one time event.