Why 72 dpi is NOT a size....

I really hate this.  Here's a scenario for you:  I offer to give a photo to a web designer and while speaking to them, I ask, "What size should the photo be?"  Their response?  "72 dpi".

I normally hit the MUTE button on the phone, emit some expletives and come back calmly with, "Yes, but what size did you need?"  This normally provokes the response of, "I told you.... 72 dpi!"  

These conversations normally end with me going to the website and figuring it out for myself, all the while wondering how this person ever makes a living working with images on the internet.

Here's the skinny.  DPI stand for dots per inch.  Its archaic really, and has little to do with anything we do today.  DPI is more appropriate for inkjet printers, but that's not what I'm talking about.

PPI is pixels per inch.  Now that is appropriate!  Still not a size though.

You see, when we speak of size of images, we need actual dimensions, AND the pixels per inch OR actual numbers of pixels.

I can hear you already...... Huh?

In other words, lets say 8"x10"@300 dpi.  Now there's a size!  Or it could be expressed as 2400x3000 pixels.  Same thing.

So, if I was told to deliver something at 72 dpi..... the obvious question is now, "What size?" right?

Hmm, lets see another example:

Lets say we have an image that measures 5"x5".  Now, thats all well and good if its a printed image, BUT, the file used to create that print could vary drastically in size.  For instance, if we had a 5"x5"@72 dpi image, the pixel count would be 360x360 pixels.  Pretty small, and would make a pretty crappy print.  On the other hand, if we had a 5"x5"@300 dpi file, the pixel size would be 1500x1500 pixels.  Plenty of information to make a great print.  See?  Simple.

I know what you're thinking..... where in the heck did we come up with 72 dpi in the first place?  Its old.... like from when people used 14 inch monitors.  Yeah, near caveman days, I know.  Anyway, its the number of pixels that a 14 inch monotor can display using 800x600 monitor resolution.  Freakin' useless today.

Oh, DPI in general is totally useless unless an image is being printed, you know, on paper?  Like a real photograph.

Got it?  Good.

-B