2. Basics of Image Processing / 2.3 Layers
Placeholder layers have no own content, but show the content of an external file. This way a document always contains the current version of a picture file - i.e. a JPEG file. Optionally, you can embed the file in the document (see chapter 7.4.55).
You can’t directly manipulate the data of a placeholder. If you want to change its appearance, you either have to modify the original file or you have to apply adjustment layers (see chapter 2.9) to the placeholder.
The easiest way for creating a placeholder is using the Placeholder Layer tool (see chapter 6.2.11). Alternatively, you can drag&drop a file to a document while holding Alt (on Windows) or Alt+Command (OS X).
By dragging a file to an already existing placeholder you can replace its content. Furthermore you can adjust its properties by using the Layer Attributes (see chapter 4.11). The Layer Attributes also allow you to control, how the fit the file into the frame of the placeholder layer. For example using the mode Clipping, PhotoLine will automatically create a clipping layer (see chapter 2.7) for the placeholder. This way you can define the visible part of the placeholder layer by moving, rotating or scaling it using the Layer Tool (see chapter 6.2.1).
When you are saving a document as PLD, placeholder layer will store a preview image in the resulting file. If the source file no longer exists, this preview image will be displayed with reduced intensity.