Screen Resolution = 72-dpi… Or does it?
I’ve produced video, print, and online stuff for years. And I’ve always just routinely set my image resolution to 72-dpi for anything going onscreen (web or video), and 300-dpi for anything that’s going to be printed. That’s always been kind of a standard I used.
And for onscreen, it would be more accurate to refer to it as “ppi’ (pixels per inch), rather than “dpi” (dots per inch). But “dpi” came from the printing industry and people often use them synonymously – even though they are two different things. Anyway…
A while back, I was reading a blog about resizing photos for online use and someone suggested using 72-dpi as a multiplier to determine how big your photos will appear onscreen. So for example, if you wanted your photo to be 6” onscreen, just multiply 6 by 72 and you’ll see that it would need to be 432-pixels. I thought, “What a great little tip. It’s simple and easy for people to remember.”
Then it hit me. I had a V-8 moment (smacked own forehead), and thought… “Wait a minute! 72-dpi has nothing to do with how big something appears onscreen! How big is the monitor? What’s the screen-resolution set to?” Those are the things that determine how big something will appear. I’ll show you what I mean.
Right now, I’m working on a 20” monitor with the screen-resolution set to 1680×1050 (roughly 98-ppi), which means a photo that’s 432-pixels wide takes up roughly 1/4th of my screen width, and measures about 4” wide (not 6″ wide).
However, if I do nothing more than change my screen-resolution to 800×600 (roughly 57-ppi), the same photo (432-pixels wide) now takes up over half the width of my screen, and is about 7-1/2” wide.
But what if I was working on a 13” monitor, rather than a 20” monitor? The images would take up the same proportional amount of the screen, but wouldn’t be the same dimensions. They would obviously be much smaller. And if my resolution was set to 800×600 my ppi would be about 77, and at 1024×768 it would be about 98.5-ppi.
Okay, so now we know that 72-dpi has nothing to do with how big you photos appear onscreen. Nor does it have anything to do with screen resolution. What about image quality? It stands to reason that the higher the image resolution, the higher the quality…right? More V-8, please.
The more I thought about it, the more I realized “dpi resolution” has nothing to do with anything. At least, not if it’s going onscreen. Printing is a different story, but I won’t get into that now.
Here’s three different images, all the same size (405×270 pixels) but with the resolution set to: 300-dpi, 72-dpi, and 1-dpi. Yes, that is “one” dpi for the last image. Can you tell the difference? For the doubters out there, go ahead and download these images and open them in Photoshop, or whatever, and look at the resolution in the Image Size palette.
(300-dpi)
(72-dpi)
(1-dpi)
So, what does all this mean? It means that if your photos are going online, dpi-resolution has nothing to do with anything. What does matter, however, is the pixel dimensions. Well… that and a whole lot of other things. Especially, how good your photo is to start with. : )
