Update: Adobe has released a fix for this issue.
I hear a lot of discussion about “banding” in images. But most of what I see isn’t banding at all. You should almost never run into banding if you are shooting RAW, careful with HSL in Lightroom, and using 16-bit working files in Photoshop.
If you’re following best practices and seeing what appears to be banding in Photoshop, there’s a very good chance that what you are seeing is actually fake banding created by Photoshop (or possibly your monitor). In fact, there are several situations in which what you see in Photoshop is NOT the real image.
In order to keep Photoshop quick and responsive, the engineers have developed some very creative shortcuts to display your layered files. This is a very good trade-off to gain performance benefits, but occasionally causes some visual quirks. In other words, Photoshop shows you an approximate preview of your image that can be significantly different from the real image under certain circumstances. The more layers you have or the more extreme the changes, the more likely you are to run into these preview artifacts.
There are a few common scenarios where this can lead you to believe there are issues in your image that aren’t real. The good news is that they aren’t an issue if you know what to look for, and there are several good solutions to see the real image when they affect your image.
False issue #1: Banding
When you are zoomed out (percentages less than 64%), you might false banding. If you zoom in to around 100% and the “banding” goes away, it isn’t real. A quick way to zoom in sufficiently is to click <ctrl/cmd>-1 for 100% zoom.
If you don’t want to zoom in and out, there’s another way you get rid of the preview artifacts: flatten the image. You can do this by right-clicking on your layers and choosing “flatten image”. Or you can make the top layer active and click <ctrl/cmd><alt/option><shift>-E to stamp all visible layers (make sure the top layer is active, or the stamp will end up in the middle of your layers). Whichever of these two methods you use, simply click <ctrl/cmd>-Z when you are ready to undo the preview.
False issue #2: Fine Detail
Another common preview issue occurs when there are fine details with high contrast. This can cause the preview to show significantly different details. The solutions to this issue are the same as for banding: zoom in or flatten the image.
The example below is easier to see in the video when you have a direct before and after, but note the outline of the buildings on the left and the brightness of the windows in the middle building. Probably not the sort of preview issue that would cause concern, but it is good to be aware of it.
False issue #3: Lines at edges of layers/masks
A third common zoom-related preview issue are false pixels at the edges of hard-edged layer masks. This shows up often with panoramas, which tends to make the image look a bit like a jigsaw puzzle when zoomed out. These edge artifacts tend to show up around 31.88, and get much worse at about 15.94% and below (with cache levels set to 4). So if you zoom in and the bad edges go away, they aren’t real.
All the solutions for banding and detail issues apply, but you have another option to prevent this particular artifact. You can reduce or avoid it by going to Photoshop Preferences / Performance and setting cache levels to 2 or 3. Be sure to restart Photoshop after changing this setting for it to take effect. Reducing cache levels will allow your files to open slightly faster, but with the theoretical slowdown in performance. I haven’t noticed slowdowns. I also haven’t tested these lower cache levels extensively, so you may wish to revert to a higher number if you encounter any slowdowns in your workflow. Do not use cache level value of 1, as you may start to run into other quirky issues based on several reports I’ve heard. Note that this fix does not help with banding or detail artifacts.
In the image below, the white jagged lines are all preview artifacts. Zooming in just a bit quickly shows that they are not real.