Today’s Question: Would you please describe the difference between a background layer and normal layer [in Adobe Photoshop] and when it is advantageous to use one over the other?
Tim’s Quick Answer: The “Background” image layer in Photoshop is simply a “normal” image layer is set to “Background” status. What that primarily translates to is that the Background image layer is locked so that certain changes can’t be applied to the Background layer. This is aimed at preserving (to some extent) the contents of the Background image layer.
More Detail: In Photoshop it is possible to have multiple image layers in a single document. That might represent a composite panorama, for example, where the multiple layers represent the several frames that have been assembled into the panoramic image. Those layers could also represent a composite image, such as when an object is added to an underlying photo, or you might use a separate image layer for image cleanup work, painting pixels to cover up blemishes in the image below.
The “Background” image layer in Photoshop generally represents the original image before adjustments have been applied. But in reality, “Background” is simply a status for an image layer in Photoshop. One of the key attributes of a Background image layer is that it can’t be transformed or moved, unless you first convert the Background layer to a normal layer. This helps protect the “original” version of the image, since you can perform your work on separate image or adjustment layers without altering the Background layer.
You can convert a Background image layer to a normal (non-locked) layer by choosing Layer > New > Layer from Background on the menu. You can also convert a normal image layer to a Background image layer by selecting the layer on the layers panel and choosing Layer > New > Background from Layer on the menu.
In general, I recommend simply leaving the Background image layer alone. That way you can preserve the “original” appearance of the image. Adjustments and other effects can then be applied by adding adjustment layers or other image layers as needed to achieve the desired result.
In other words, if you need to use a layer for a task in Photoshop, it will be a normal layer rather than a Background image layer. If you need to perform a task that requires you to work directly on pixels (such as with many filters) you may need to create a copy of the Background layer for this purpose. For many other tasks (such as most image cleanup work) you can simply use a new empty image layer for that work.