The other day I was printing some photographs and noticed when looking closely that there were some cut lines across one of my images.
Interpolation is something that, for the most part, goes unnoticed in Photoshop. I didn’t think too much of it either until I started seeing this jagged edge problem on a couple different photos. Normally I would disregard an issue like this as a resolution or an anti-aliasing problem but the lines are too uniform across the entire image for either to be the case.
As it turns out it is the Free Transform and Ruler tools that cause these lines because they use interpolation to perform their operations. In Photoshop’s default settings the interpolation method for all tools is set to Bicubic Automatic so you shouldn’t ever run into this problem unless your settings get changed. I won’t go into detail on all the interpolation methods that Photoshop has to offer but essentially what interpolation does is create or delete pixels depending on whether you want to size an image up or down from its original size. Interpolation also plays a part in rotating images which is why this issue is hard to find an answer for online. Interpolation is usually just associated with sizing images up or down but not rotating images.
After going through each of the interpolation options and trying a few free transforms I figured out that it’s the Nearest Neighbor (Preserve Hard Edges) interpolation option that causes this jagged edge problem after a free transform rotation or straighten with the ruler tool. The solution is simply to change your image interpolation setting back to Bicubic Automatic if it’s been changed which is what happened to my interpolation settings at some point without realizing it. To change your interpolation settings you can go to your Preferences in Photoshop by hitting Command+K (Mac) or Control+K (PC) and changing them in the Image Interpolation drop down menu under the General section.
You can also change your interpolations settings on the fly when you are using the Free Transform tool (Command+T) by using the drop down menu on the Free Transform options bar at the top of the screen.
Here is the same image from the beginning of the post rotated with the Bicubic Automatic interpolation setting
Notice the lack of vertical lines in this crop. This problem shouldn’t ever occur while editing a digital image because it is digital. There will certainly be artifacts while upscaling an extremely small image to become billboard size but in a relatively small rotation like this there should not be so many artifacts, or at least not out of a file from a DSLR.
Until next time!