I decided to write this post after having too many heated discussions with many users across many blogs. After hearing repeatedly; "The iPad will have a better display" or "It sucks because it's not Retina" I figured it was time to break the argument down and dispel the "Retina" myth.

The Basics: What is "Retina"?

Let's start with Apple's definition of "Retina Display"

From iPhone description:"Thanks to the Retina display, everything you see and do on iPhone 4S looks amazing. That's because the Retina display’s pixel density is so high, your eye is unable to distinguish individual pixels." -- Apple.com From iPad description:

"Those pixels are so close together, your eyes can't discern individual ones at a normal viewing distance." -- Apple.com From Retina Display Introduction

"It turns out that there's a magic number right around 300 pixels per inch, that when you hold something around 10 or 12 inches away from your eyes, is the limit of the human eye to differentiate the pixels." -- Steve Jobs @ WWDC

From these descriptions we can take-away that Apple's definition of "Retina Display" is the inability to discern the individual pixels from certain "normal" distances. That certainly sounds impressive, but in actuality that claim can be made about any display based on screen size, resolution and viewing distance. For example a 50" 720P (1280x720) television is "Retina" from 9.8 feet away and that display has only a 29.4PPI pixel density. More on this below.

The Math: Finding the "Retina" Sweet Spot

Now that we know how to define a "Retina" display, how do we go about finding the right resolution for to achieve this?

The answer lies in knowing the visual angle a human eye can resolve images and applying a little math. For 20/20 vision, that angle is 1 arc minute, or a MAR (Minimum Angle of Resolution) of 1 minute. All that really means is: At a given distance, if two objects resolve at less than 1 arc minute, you will see them as one object. For displays the distance between the pixels is called dot pitch. It isn't used much anymore as a selling point but if you remember the old CRT days, you would see monitors advertised as having a .28 dot pitch.

Now that we have most of our variables, we can figure out the visual acuity, or viewing distance where pixels are indistinguishable from one another. I won't bore you with all the calculations, but the important one looks like this:

VA=dot pitch/(2*tangent(rad(((1/60)(20/20))/2)). So let's look at the visual acuity of some popular resolutions on tablet-size screens.

Device(screen size) Resolution Dot Pitch Pixels Pixel Density Visual Accuity iPad 2 (9.7") 1024x768 0.008 786K 132 26.1" New iPad (9.7") 2084x1536 0.004 3.15M 264 13" Lenovo Tablet 2(10.1") 1366x768 0.006 1.05M 155 22.2" Surface Pro (10.6") 1920x1080 0.005 2.1M 207 16.5"

What the table above means is: further than about two feet away, ALL of these resolutions are "Retina" to someone with 20/20 vision.Read that last sentence again. Let it sink in... All. Of. Them. That leaves one variable remaining: actual viewing distance.

I Can See My Tablet From Here: Average Viewing Distances

I was going to go in to a long example of average human height, limb length and various usage scenarios, but his post is getting a little long in the tooth already. Suffice to say, my findings pretty much agree with averages than can be readily found through searching the web. Display Mate, TAUW and the American Academy of Optometry all seem to agree on a range of 15"-22". I feel the 15" distance is a little close based on how I personally use these devices, which I hope to illustrate below.

Please let me know if these scenarios look similar to how you use/would use a tablet.

So let's take a look at the visual acuity numbers again and see which devices qualify as "Retina" at that distance.

Tablet Resolution Visual Acuity Is Retina? iPad 2 1024x768 26.1" NO Lenovo Tablet 2 1366x768 22.2" YES Surface Pro 1920x1080 16.5" YES New iPad 2084x1536 13.0" YES

That's right even the lowly 1366x768 resolution is "Retina" at more than 22". The only device in this list that doesn't make the cut is the iPad 2. It's one of the main reasons that iPad users rave about retina display. They're among the few that are actually benefiting from the increased resolution, which says more about how sub-standard the old display was than how great the new display is. Don't get me wrong, the New iPad's display IS fantastic, but it has more to do with the enhanced contrast & expanded color gamut than the PPI. Those two improvements are much more critical to the viewing experience (but that's a whole different article).

For comparison, take a look at what holding a tablet 12"-18" away looks like:

OK, so maybe 22" away is pushing the limit just a smidgen, but 1366x768 is clearly not the "crap" resolution that it is being portrayed as. On a 15" laptop probably, but not on a 10" tablet. I think we all have to agree though that 1920x1080 or 1080p on a 10"-11" screen clearly qualifies as "Retina" since the visual acuity is around 16" for that resolution.

What Apple has done here is create a "density war", much like the mega pixel war that raged in the digital camera world a few years ago. We all know there are 9MP cameras that take much better pictures than 21MP cameras. The same applies. Apple did what they always do. They took the path of least resistance and sold it as a "feature". They chose 2048x1536 because it gave them an easy way to handle scaling of applications as they just doubled everything. It was not because it was the best resolution for viewing their devices. Nor was it the best choice for the customer. Read on to find out why.

But I needs the MOAR Pixels: Diminishing Returns & Performance Hits

By now you may be saying to yourself, "Fine, 1080p is 'Retina' on a tablet. But what's wrong with having a higher pixel density?"

The answer is simple. For every uneccessary pixel above visual acuity you add, your device runs slower, hotter & has less battery life.

Any PC gamer will tell you, the higher resolution you're running the fewer FPS (frames per second) your game will run. Hence the need for multi-GB, multi-card gaming rigs to push maximum pixels at high frame rates. All the processing power it takes to push those pixels creates heat, and the hotter a chip runs, the slower it runs. Again, gamers solve this with liquid-cooled systems and large fans.

Retina Displays put un-needed strain on the GPU pushing pixels you can not even see (over a million "invisible" pixels). How much snappier could your iPad be? How much cooler would it run? I guess you'll never know.

As far as power goes, we all know the New iPad is thicker than the iPad 2. We all know it's because it has a larger battery. What you may not know is that the battery has a 70% higher capacity. That's right, almost double! Yet it takes LESS time to run that battery down to zero. Displaymate shows that the New iPad gets about 5% less run time as the iPad 2 at middle brightness and about 20% less run time at maximum brightness. The back light alone uses 2.5 times the power of the iPad 2, and that's before you start illuminating those 3.15 million RGB pixels. Think about it this way... put the New iPad battery in an iPad 2 and it could run continuously with the screen on for over 20 hours.

Perfect PPI: 1080p for Tablets

This is why the title says the Surface Pro has a "better" Retina display than the iPad. At normal viewing distances, there is no difference. None. Zero. Nada. The end result gives users an amazing visual experience while leaving more GPU headroom for things like scrolling, hardware-accelerated browsing, better games & more. It provides better battery life & less heat. Lastly they cost less to produce, which in turn lets manufacturers put more resources into things that matter more like brightness, higher contrast and wider color range.

After all, anyone who thinks it's all about pixel density is just...well...dense.