Today’s Question: Further to the question about adjustments reducing image quality, is image quality reduced if I make many small adjustments on adjustment layers [in Adobe Photoshop] that cumulatively result in the effect I am after? Is it better to make fewer but stronger adjustments? I often just make a second Curves adjustment layer to refine the effect of my first Curves adjustment layer. Somehow that just works out better for me. Is this a problem?
Tim’s Quick Answer: There is a minor benefit to using only one adjustment layer rather than two assuming the same final overall appearance for the photo. However, having more than one adjustment layer of the same time isn’t problematic enough that I would tell you to avoid doing so if you find that workflow easier.
More Detail: Today’s question was a follow-up to a previous question about the impact of applying adjustments via adjustment layers in Photoshop compared to direct adjustments. In my answer I mentioned that one of the benefits of using an adjustment layer is that each layer only really counts as a single adjustment, even if you have revised the settings for the adjustment layer multiple times.
In other words, applying multiple direct adjustments to an image can have a negative impact on image quality based on cumulative adjustments. An adjustment layer, by contrast, only counts as a single adjustment based on the final settings for the adjustment layer.
If you add more than one adjustment layer of the same type, of course, you are applying more than one adjustment. That could potentially result in a slight loss of image quality. The most common issue is posterization, which appears as the loss of smooth gradations of tone and color in an image. Multiple adjustments of the same type would increase the risk of these types of issues.
That said, image quality degradation is generally only a real concern when the adjustments are very strong. If you are simply fine-tuning an existing adjustment with an additional adjustment, the impact will generally be very minimal.
In general I recommend using a single adjustment layer for each type of adjustment you want to apply. This not only helps ensure optimal image quality, but can also help streamline your overall adjustment workflow. That said, if you find it easier or more comfortable to add a new adjustment layer rather than revising an existing adjustment layer, as long as those refinements are relatively minor I wouldn’t be worried about the impact on image quality.