Finding margins for a centred photo
The following is a simple calculation for finding out the margin values to set on a printer to print a photo vertically and horizontally centred on a piece of paper.
This will only work on photos that are 'less square' than the paper, as a square photo can only have equal margins on a square piece of paper not a rectangluar one and vice-versa. As a trivial example, a 3x2 aspect ratio photo will print in the centre of a 7x5 inch piece of paper if the margins are set to half an inch. The calculator below is useful where the maths is not so easy, such as a 3x2 aspect ratio photo on A4 (297x210 mm) paper...
Margins = 18mm, Photo Size = 261×174mm
Diagram to approximate scale (paper is light grey with a thin line around the edge, photo is darker grey):
297×210mm paper
261×174mm photo, 18mm margin
