Apr 27 2009
You can make a new file that mimics the dimensions and resolution of any other
saved file Photoshop has open by simply going to the File menu and choosing
New and then go to the Window menu and select from the list of open documents
at the bottom of that menu or choose it from the bottom of the Preset menu in
the New dialog box. Now, magically, the width, height, resolution and color
mode settings in the New document dialog box match the chosen document.
Note that since you can only create new files in Bitmap, Greyscale, RGB, CMYK
or Lab color modes, you may only match the specifications of files in those
modes when using this maneuver. Thus, you cannot match the dimensions of an
Index Color image in this way; Photoshop will seem to oblige but at the last
second it will error on you.
Another method of creating a new document the size of another is to open the
document you wish to match, choose Select All (Command-A) from the Edit menu
and then select Copy (Command-C) or Copy Merged (Command-Shift-C) if your file
has layers. Now when you ask to create a new document, Photoshop will automatically
plug in the dimensions of the image in the clipboard as the specifications of
the new document.
The downside of this method is that you will have to replace whatever you might
have in the clipboard with your chosen image which, if it is quite large or
multi-layered, may take time and memory resources you might not have.