There's now also a thread on Topaz Sharpen AI on GetDPI on this:
Topaz artefactsHere's my post with some test results:
I exported an image from about 2000 pixels from Lightroom, it gave very similar artifacts in Sharpen AI along the blue sky top border.
so it seems C1 is not the culprit. I thought it was very unlikely that it would, but now we're sure.
Edit 2: Here's my two examples:
Exported from LR, without any sharpening (slider at zero in the converter, none in the export dialog)
Above image, sharpened in Topaz AI (default parameters) ==> Artifacts galore along the top border
And added just for fun, first image, sharpened with Topaz Detail (minor small and middle details and .10 deblur) ==> No artifacts and slightly different result from sharpen AI on the statue, can't really decide which is better, they're just a tiny bit different.
Further it was suggested in the thread that the raw converter can have an effect but the thread shows there is little difference between Lightroom and C1, and I can't imagine Topaz not training their AI models on these two quite popular and widely used raw converters.
It was further tested and the artifacts do not appear when exporting the file without downsizing and then running through Sharpen AI
However exporting a downsized tiff (8 bit and 16 bit) gave the same artifacts as running sharpen AI on a jpeg.
So it seems downsizing is the culprit leading to the artifacts in solid colour areas.
I have reported this issue to Topaz this is what I got back:
I just tested your image on my computer and I can reproduce your issue. I will discuss with the leader of our R&D team to see if we can figure out the reason of this issue.
My suggestion for now is please try to use Sharpen AI before Lightroom adjustments. Our AI model sometimes can be sensitive and typically can do the best job on the very original image.
I find the advice kind of lame, since final sharpening for output size is usually done as the last step and at output resolution (at least that's how I get the best results, YMMV) and not as a first step before making any adjustments. I find capture sharpening in Lightroom (and C1) more than adequate and don't need Topaz sharpen AI for that step.
I'd be interested in your experiences (similar or otherwise) or some suggestions how to avoid this issue on downsized raw converter exports.