As a Serif customer, I was offered Serif Photo Zoom, their photo-enlarging program at £23, (80% off). I had a look at the reviews and these were generally positive, so I thought I would give it a try. I chose a photo of a male Chaffinch taken in the cafe gardens on Tresco, Isles of Scilly. I reduced it first to 50%, then to 25% and then used PhotoZoom, Serif Affinity and Photoshop CC2017 to resize back to the original. There was no subsequent post-processing.
#1 Here is the original at 100%, cropped from the original image.
#2 Reduced to 50%, then enlarged back to the original with Photoshop
#3 Reduced to 50%, then enlarged back to the original with Affinity Photo
#4 Reduced to 50%, then enlarged back to the original with Photo Zoom
#5 Reduced to 25%, then enlarged back to the original with Photoshop
#6 Reduced to 25%, then enlarged back to the original with Affinity Photo
#7 Reduced to 25%, then enlarged back to the original with Photo Zoom
One thing is clear. None of them make a good job of the detail in the 25% reduction/enlargement. However Photo Zoom does make a better job of the not-so-fine detail. Look at the white feathers on the wing. They do seem clearer in the Photo Zoom image.
Looking at the 50% images, there is less to choose between them, but I still think that Photo Zoom has done the better job.
Overall I think it is a good buy. I have a number of images scanned from slides where I saved them as too small. Photo Zoom may well rescue these into a usable form.
Edit: In my original posting, I had sharpened the final images. I have now reverted to unsharpened versions.
Comment welcome.
John