The attached sample is from a piece of clip art 640 pixels wide. In general, with a little tweaking, TPAI does a good job of enlarging and sharpening the images. However it’s often “over-enthusiastic” with sharpening bokeh, or anything deliberately out of focus.
In this screen grab, with the untreated image on the left, the issue is particularly apparent in the over-sharpened ridgeline in the background, although there are artifacts around the clouds, too. In the original image there are two cowboys on horses, and they’re masked as the subjects. The background terrain isn’t masked.
I expect TPAI to clean up obvious pixilation, not give sharp edges to the out of focus ridges.
My current work-around is use GIMP to smear the too-sharp lines. Is there a way to get TPAI to be generally kinder to bokeh?