Why does Imagemagick convert make the first page of output PDFs too large?

Question

When I run

convert *.jpg output.pdf

the output looks like this:

Why is the first page bigger then the others in the PDF? The original JPEGs were all the same size!

Answer 1

A JPEG image can store a resolution (i.e. pixels per inch) in addition to its geometry (actual number of pixels). convert uses the resolution when converting JPEGs to a PDF. It's probable that the first image has a lower resolution than the others. If they have the same size in pixels, then an image with a lower pixels per inch will be bigger.

Try running identify -verbose file.jpg on a couple of the images. Look for the "Resolution:" and "Print size:" lines near the beginning of that output.