There is a myth…about 72 ppi

I was browsing through my rss reader trolling my favorite sites when I came upon an article that interested me. Then I found another link on that site to something else…20 clicks later…only God knows where I ended up, but it had me engrossed for quite a while. I wish I could remember where, cause I would post the link, but I was on a different computer.

Anyway it was an article about saving images for the web at 72 dpi. The funny thing is, dpi is what most of the web designers I know refer to it as, but that is a printing thing (dots per inch). PPI is the one dealing with screens. Pixels per inch, and that is the one that matters.

Now, I am not sure if there is a way, once a photo has been taken, to adjust the number of pixels per inch in Photoshop. What I do know is that most web designers save their images at the 72 resolution. You could very well be one of them. Well…so am I. And even knowing what I know today, I doubt I will change that habit. Why? Because it doesn’t matter.

I would like anyone reading this that is actually interested now, to do something. Open an image in Photoshop, and go to Image>Image Size. In that window, make sure the Resample box is UNCHECKED. Now, if it isn’t already at 72, change it to that, and then save it as a jpeg. Then do the image size again, and change the 72 to say…3000. Notice with the Resample box unchecked, the pixel width and height stay the same, they are locked in. Save that also as a jpeg.

Now place both of those images into an html file, and preview it in a browser. What do you notice?

Not a damn thing, right? They both look the same. Now right click on both of the image files, where ever you saved them, and check their properties to see each’s file size.

What do you notice? They BOTH have the same file size. So what does this tell you? That for people in web development, that whole 72 thing is a bunch of bull. That resolution means NOTHING in the web world. It does however matter if you printed them. Cause you probably noticed that the Inches size changed. But screens don’t go by inches.

So what this means is, what you really have to pay attention to is the Pixel width/height. That and the compression you use when you save for web in Photoshop (or Fireworks, or whatever it is you use) is what matters for the file size.

I know, that just blew your mind, right? Feels like you just found out that what you believed in was all just a big fat lie.

So, will this change how you save images? I’m guessing not. It IS interesting though. Next time someone pulls the whole 72 whatever-p-i…you can tell them they have no idea what they are talking about and pull out your new found knowledge, and look like a super smarty pants.

Tags:

One Response to “There is a myth…about 72 ppi”

  1. Oh I know the feeling of traveling from blog to blog, eyes glazed over (it’s the damned link bait!)

    I have actually attempted to adjust the dpi to see what would happen, and you were right, not a thing. I do need to look further into image optimization though. Now that I’m starting to use photoshop, I can’t get an image below 100kb without artifacts.

Leave a Reply to Joseph McCullough