You got a shiny new Apple iPhone 4, right? You love that retina display! But, none of your other devices have one! What are you to do?

All your peers have a shiny new Apple iPhone 4 with its amazing retina display! Your phone is feeling blue, not having a retina display of its own. What are you to do?

It's simple!* Just create your own retina display. All you have to do is follow these easy instructions and all of your devices will have their own retina displays! We'll call this Retination: that act of making a retina display out of a normal display.

Stage 1: Determine Device Pixels Per Inch

First, you need to determine the pixels per inch of the device you want to retinate. You can do this by looking up the specifications for "ppi" or "dpi" or use simple measure the width and divide the width in pixels by the width in inches. Apple's documentation says their retina display is 326 ppi. Your display will be different. As an example, we'll use the Motorola Droid. It has a ppi of about 265.

Stage 2: Determine the Distance of Retinality

Now, using the same trick Apple uses to call the iPhone 4 display a retina display, you'll determine this for your display. The human eye has specific, well known optical characteristics. That is, the effective resolving power of the human eye for someone with 20/20 vison is, and has been, measured and agreed upon (just check Wikipedia!).

Using this data, we can determine the distance at which a display becomes a retina display. For the iPhone 4, Apple states this is 10-12 inches. My own calculations show that this correct; I get 10.4 inches. I don't know about you, but I don't hold my phone up that close to use it. I do a pinch-zoom and hold it farther away.

Anyway, the formula to convert PPI to DTR (Distance To Retinality) is 3438 * (1/PPI). The 3438 number is the scaling factor number derived from a 1 arc-minute visual acuity for a person with 20/20 vision.

Keeping to the Motorola Droid, we can now calculate that its display needs to be a whopping 13 inches away to be retinated! Gosh, more than a foot away before you can't distinguish pixels? The Horror!

Stage 3: Using Your New Powers of Retination

Now that you're empowered to retinate all of your displays, don't hold it over your Apple iPhone 4 toting friends too much. Their display is still a higher density and retinates so close you'll feel cross eyed when trying to unretinate it. And, there's no doubt; it's a nice display, retina or not.

Some Examples

I went ahead and calculated the distance to retinality for a number of common devices.

• A Nexus One display retinates at just under 14 inches
• The Evo 4G, with it's large display, retinates at nearly 16 inches
• The Archos 5, with an even larger display, retinates at almost 18 inches
• The T-Mobile G1, having a small, but low resolution display, needs 19 inches to retinate
• The Nokia N900 has a 3.5" display and high enough resolution to bring it's distance to retinality down to just 12.9 inches. That's 2nd only to the iPhone 4, currently.

That is, every one of these devices -- even the low resolution T-Mobile G1 -- can easily retinate within arms length.

What about your computer, laptop, and TV? I've calculated a couple of common display sizes:

• A 15.4" MacBook Pro sporting a 1440x900 display retinates at 31 inches, just over 2.5 feet. That's about my normal working distance at my desk.
• A 24" monitor with a standard 1920x1200 resolution takes 3 feet to retinate. That's not a terrible working distance, but I'm usually closer and the display definitely appears grainy.
• A 30" monitor with a standard 2560x1600 display, however, needs just 34 inches to retinate. That's definitely a great working distance for these beasts. Apple even makes one of these. Apparently they didn't realize they already had a display on their hands that was often used at the retinality distance.
• A 40" FullHD (1920x1080) TV needs just over 5 feet to retinate. A 40" TV with a sloppy 1280x720 Half HD (720p) display needs nearly 8 feet to retinate. This means two things. First, it means that if your TV is closer than either of these numbers, it's big enough to truly see the details. Second, it means if your 40" TV is under 8 feet away, an average person can easily see the difference between 720p and 1080p. For bigger TVs, this distance increases. Going Full HD does, mathematically, make a difference to the average human eye. ;)

Did you enjoy this retination of your display?

Now go out and retinate something!

(*Note: Yes, this is meant to be a little tongue-in-cheek. However, the math should be accurate. A Discover magazine blog post brought these numbers to my attention. I also checked with Wikipedia.)

(UPDATE: 7 July, 2010: Added Nokia N900.)

Posted by Shane on July 3, 2010 12:30 PM | Permalink