Today’s Question: Does cropping an image in Photoshop, and especially cropping multiple times, degrade the quality of the image?
Tim’s Quick Answer: While aspects of cropping in Photoshop can be performed non-destructively, if you rotate or resize as part of the crop that will slightly degrade the image. Rotating or resizing by cropping multiple times would compound that issue.
More Detail: Today’s question was a follow-up to a recent question about cropping multiple times in Lightroom Classic. As I noted in my answer to that previous question, there is no degradation in image quality caused by adjusting the crop settings multiple times in Lightroom Classic. In effect, only the final settings that are established when you export or otherwise share the image count, as though you had only made one change to the crop settings. This same concept applies when making multiple updates to the crop setting when processing a raw capture in Camera Raw.
In Photoshop things are a little more complicated because you are working on actual rendered pixels rather than a raw capture that has not yet been full processed and rendered.
You can use a non-destructive crop in Photoshop by making sure the “Delete Cropped Pixels” checkbox is turned off on the Options bar when using the Crop tool. When this checkbox is turned off the pixels you crop won’t actually be deleted from the image, but instead will be hidden outside the image canvas area. You could later reveal those cropped pixels by choosing Image > Reveal All from the menu.
However, it is also possible to resize and rotate an image as part of the crop in Photoshop. Those adjustments would alter the actual pixels in the image, which causes at least a minor degradation in image quality. If you resize and rotate multiple times by cropping multiple times with the Crop tool, that degradation will be amplified.
It is important to note that the degradation in image quality here would generally be very minor and difficult to see in the image. I think it is also important to keep in mind that rotating to fix a crooked horizon, for example, is more important than avoiding the very minor degradation in image quality that the rotation might cause.
Considering all the above, however, if I realized I didn’t get the image rotated perfectly with the first crop in Photoshop, I would prefer to undo that crop and apply a new crop with a better rotation setting, just to try to preserve image quality as much as possible.