Understanding Resolution Sizes

Today I'd like to talk a bit about resolution sizes and what they mean. There are a million tutorials out there that get into the technical stuff and it can get pretty complicated. This is NOT one of those tutorials. If you want to learn exactly what a pixel is, you may want to do a search on the web. I am just going to talk specifically about what resolution sizes mean when it comes to printing, verses the web and how to size everything up.

The first thing we are going to discuss is PPI (or DPI). PPI and DPI stands for pixels per inch and dots per inch and essentially they are the same thing. The only difference is that one relates to printers and the others to your screen. What the numbers mean is how many pixels are packed into a square inch. So a 300 PPI image has 300 pixels in one square inch and a 72 PPI image has...you guessed it, 72.

One thing to keep in mind is that a print and a monitor will show your image in completely different ways. When you are preparing a photo for print, you want as much resolution as you can get. You should plan on at least 200 PPI and 300 or more if the image is larger than an 8x10.

So why don't we just make ALL our images at 300 PPI? Simple, file size. Your monitor can't tell much difference between an image with 72 PPI (which is standard for the web) or 300 PPI. And a 300 PPI image is MUCH larger and it takes forever to load up. So when you are saving your images, anything for the web should be saved at 72 PPI and anything for print at 200 PPI or more.

One question I hear a lot is, "Why does my image show up in Photoshop as 72 PPI? I want my camera to shoot at 300!" The truth is, a digital image has no exact resolution or size. The resolution will change as the image size changes because the resolution is being spread over a larger or smaller area. If you change the image size in Photoshop from 72 to 300 PPI, you will then see the resolution numbers get smaller. In actuality, the image is still the same size.

The other question I hear a lot is, "How do I size my image for the web?" Well, we already know that the PPI should be set at 72, but how do we figure out the rest? The first thing to do, is forget about trying to size images for the web using inches. You monitor only sees pixels and has no clue what an inch is. The second thing is to realize that everyone's monitor is set to a different resolution. A screen size set to 800x600 is going to show images a lot bigger than someone who has a screen set to 1024x768.

If you have your monitor set to 1024x768 and you crop your photo to that size, then your image will fill the entire screen. When I save an image for web viewing, I generally find that 600 pixels at the longest side is a good size. If I want to paste an image into a signature on a message board or place an image in a post, I would probably go a bit smaller so that the image doesn't look too big for them. Usually 300-500 pixels max is a good size.

Hopefully this will clear up the confusion and make things easier for you when posting to the web. Just remember the most important rule! When you resize an image (for print or for web), be sure to save it with a new name so that you don't lose your original. Never save over your original; you never know when you'll need to go back to it!