Quad HD vs 1080p vs 720p comparison: here's what's the difference

So what is Quad HD all about and what are the benefits it brings? As with any improvement in screen resolution, Quad HD will make smartphone screens clearer, “sharper”. The practical benefit of such a sharp display is that your eye will be able to make out the tiniest of detail in images and videos, as well as read the tiniest of fonts.

But some may ask: wasn’t that the whole point of ‘Retina’ displays way back in 2010? Hadn’t we already reached that retina-perfect picture on our devices? We’ll answer this question right away.

Screen resolution and display size: are we there yet?

Let’s first start with the iPhone 4, a smartphone that first claimed it comes with a ‘Retina’ display so sharp that the eye of a regular person no longer sees jagged pixels. The iPhone 4 was a device with a resolution of 640 x 960 pixels, but resolution alone does not tell us much about the sharpness of the display itself. After all, if you put the same resolution that looks clear on the iPhone on a 50-inch screen it would suddenly start looking not sharp at all. So instead of looking at resolution alone, it makes much more sense to look at a metric like pixel density, calculated using both screen size AND resolution.

The iPhone 4, for instance, featured pixel density of 326 pixels per inch (ppi, but some would also say dots per inch, or dpi).

Not long after, though, higher resolutions and pixel densities started to appear. Here are the pixel densities of some popular phones since then:

• 
  Apple iPhone 4-5s: 326ppi
• Samsung Galaxy S3 (4.8-inch, 720p): 306ppi
• Samsung Galaxy S4 (5-inch, 1080p): 441ppi
• Samsung Galaxy Note III (5.7-inch, 1080p): 386ppi

By looking at these different phones, we can again see how screens with the same resolution have different pixel densities, and thus different sharpness.

Back in the day when Apple unveiled the iPhone 4, various reports suggested that anything above roughly 300ppi is good enough for the human eye to perceive as clear and sharp. Why then screen resolutions continued growing and growing until present-day Quad HD devices?

The latest Quad HD smartphones come (or are expected to arrive) with a pixel density as high as (the seemingly unnecessary) 534ppi! Is it really just new technology for nothing?

The third factor: viewing distance

There is another key factor that should be considered when we speak about display sharpness and clarity, though, but it’s often left out of the conversation. We’re speaking about viewing distance. Even the sharpest of TVs and the sharpest of phones starts to look flawed when you look at it from a very close distance. Look at the same device from a 1-foot distance and the clarity of the picture suddenly becomes better. Look at it from further away, and the picture would appear perfectly sharp and clear.

The question that we will answer today then is: at what viewing distance one starts actually seeing the benefit of high-res displays?

The ideal viewing distance

To measure the ideal distance between you and your smartphone display, we’ll assume you are one of the rare few who have very good vision. You’d often hear about such vision being called 20/20 vision. A person with 20/20 vision is one who can discern detail of 1 arc minute (1 arc minute = 1/60 of a degree = a circle has 360 degrees, so 1 arc minute = 1/21600th of a full circle). Most people have worse vision than that - for instance someone with 20/40 vision can only discern detail of 2 arc minutes, while the rear few (think jet pilots) with 20/10 vision can discern detail of 0.5 arc minutes. The actual limit of human vision is around 20/8, so again, we’re assuming a fairly optimistic 20/20 vision scenario.

So with all that in mind, how close do you need to be start seeing those pixels and details on even a Quad HD smartphone? And what about 1080p phones, and 720p devices? Take a look below:

• Typical 480p phone (4” display like Galaxy S III Mini): eye starts to notice pixelization from 14.73” (37.4cm)
• Typical 720p phone (4.7” display like Nexus 4): eye starts to notice pixelization from 11” (28cm)
• Typical 1080p phone (5” display like Galaxy S5): eye starts to notice pixelization from 7.8” (19.8cm)
• Typical 1440p phone (5.5” display like expected LG G3): eye starts to notice pixelization from 6.44” (16.4cm)

Conclusion

reference: Carlton Bale, jaredjared.com