I have several images in a folder, these images are all 1920x1080 pixels in size. I want to open them as layers in a single project so I open a new document in Photoshop at 1920x1080 and drag the images from the folder into the photoshop document. For some reason, PS keeps resizing them to be smaller than 1920x1080 when I drag them in like this despite the fact they are the exact same size as the document resolution. Under Preferences > General, I have "Skip transform when placing" turned OFF because I don't want to have to confirm each and every image placement, and I have "Smart Objects when placing" turned OFF because I don't want to use smart objects. "Resize image during place" seems to do nothing. What am I doing wrong here? I need to be able to drag in multiple images to make layers at their true full size!
It seems to work properly is the new document is set at 1920x1080 300 pixels/inch rather than 72 pixels/inch... What is the difference, aren't document pixels true and pixels/inch only relevent for printing (DPI)? How does a document have different "dimensions" AND "resolution"??
A standard copy/paste will align the pixels in the documents without any regard for ppi. A 1920 x 1080 at 300ppi will paste onto a 1920 x 1080 at 72ppi and match completely. This is the native behavior. Only pixels matter.
Smart objects, which is what you get when you drag, are designed to honor physical dimensions instead of the native pixel dimensions. They do this by reading the ppi number and calculating the resulting physical size.
This can be a bit confusing at first, but it was done this way for compatibility with vector applications like Illustrator. It's the only way to make PS and Ai treat the concept of "size" identically. In effect, a smart object makes a raster image file behave as if it was a vector file.
But yes, natively in Photoshop, the image is just pixels and ppi is just metadata.