Resolution is one of the most misunderstood photo concepts so I’ll be glad to give you a walkthrough.
Resolution is literally dpi – dots per inch. Think about a 4×6″ print. The more dots per inch, the more resolution. Make sense?
Let’s talk math for a second.
A 4×6″ print at 100 dpi is literally 4×100 * 6×100. Does that make sense? 400×600 pixels total.
A 4×6″ print at 300 dpi is literally 4×300 * 6×300. That’s 1200×1800 pixels total.
So the 2nd print is obviously higher quality – and it’s a larger total image.
Let’s do one more. An 8×12″ print at 100 dpi is 800×1200 pixels. At 300 dpi it’s 2400×3600 pixels.
Ok, now here’s the thing I want you to see – the 4×6″ at 300 dpi is 1200×1800 pixels. The 8×12″ at 100 dpi is 800×1200. The 4×6″ is technically better quality of a print. But what happens if you put them online? An 800×1200 displays on your monitor at 800 pixels by 1200 pixels, no matter what. Your monitor has a set number of pixels. If your monitor is set to 800×1200 resolution and you display the 800×1200 it will take up the entire screen. Whether it’s a 4×6″ at 200 dpi or an 8×12″ at 100 dpi – they’re the same pixel dimensions. Does that make sense? What’s 4×6″ at 200 dpi? 800×1200 pixels. And 8×12″ at 100 dpi? 800×1200 pixels – same! One has DOUBLE the resolution – but the pixels are all that matter.
So in the end, don’t think about resolution except in printing. Think about output. What size do you want the image to appear on the monitor? Size it to that in pixels.
Matt