Image Sizes

[Claude J Greengrass]

For computer screen images - multiple the inch dimensions by 72 and you'll have the pixel dimensions. So if your image is 4" x 5" that equals a pixel dimension of 288 x 360 pixels.

For aspect ratio divide the longer dimension by the smaller dimension. So a 4"x5" image would have an aspect ratio of
1.25. also written as 1.25:1 Note that it doesn't matter if your image is portrait or landscape - 4" x 5" or 5"x 4" the aspect ratio is still 1.25

I used to believe that 72 DPI was true for "all" computer screens. That was until I got hooked into ChromeOS and the Google infrastructure. I wanted to print a template for a painting from a photo I had taken. Gimp scaled, cropped, and guillotined into a set of images of the size my b/w printer could handle. I inserted them into a gdoc, a Google word processing document format, for printing as this was the tech that I had working at the time. I was surprised that the final images were 80% of where I started. I carefully checked that GIMP had processed them correctly. Yes, each was exactly X by Y inches. When I checked on my Chromebook, the image of 80% of the size I wanted. Moral to this story: Google gdocs embed images (jpegs) at 90 DPI so caveat emptor.