Harmonize suddenly produces very pixelated results

There is a workaround that you can (sometimes) use. It works as follows: determine which area of the photo will be affected by Harmonize, and crop this out using the crop tool with ‘delete cropped pixels’ unchecked. That normally means you will select the object, and the area around it where Harmonize might add a shadow. Now use Harmonize. Harmonize will now re-render only the cropped image, so a much smaller image. That means the result will have a (much) higher resolution. The more you can crop, the better the resolution. When Harmonize is done, select menu ‘Image - Reveal All’ to undo the crop and get the full image back.

OK, thanks for the feedback. So that settles the matter, and the cause is the limitation in harmonization. 

Harmonize re-renders the entire image (and then masks out the result). As its resolution is limited, this is to be expected for high resolution images. The higher the image resolution, the more you’ll see the difference.

​@c.pfaffenbichler c.pfaffen Sure!

Here before and after using Harmonize, and thrid screenshots shows the lower resolution

If needed, I can also provide screenshots showing the original image and the resulting Harmonize output at 100% zoom.

Please do. 

I think Harmonize is limited to 2048px x 2048px, though I might be mistaken. 

Edit: A quick Google-search turned up claims that the limit might even be 1024px x 1024px, but I expect those posts might be obsolete.