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Retina displays, 4K TVs push pixel limits

By: Rob Pegoraro 20 March 2012

“High definition” may need a re-definition.

In the tablet market, beyond-high-resolution screens like the new iPad’s “Retina display” offer the promise of onscreen graphics as sharp as anything gracing printed pages. In the big-screen business, meanwhile, manufacturers are working on “Quad HD” and “4K” televisions with about four times the resolution of 1080p HDTVs. new ipad screen

I see a bright future for one of those efforts. Hint: The industry would do well to think small.

On the new iPad, its 2,048-by-1,536 pixel resolution constitutes an obvious and overwhelming win. You can skip the usual “zoom in to make the text legible” stage of reading Web pages–even fine print like photo credits is free of jagged edges.

That’s because the pixels that usually form bitmapped stairsteps up close are too small to discern without squinting through a magnifying glass.

It’s an amazing piece of work. The $499-and-up new iPad–with three million sold in its first weekend–may redefine how handheld screens should look. Once you see that a display can have the same sharpness as print, it’s easy to expect that out of every screen you might hold before your face–tablet, e-reader, laptop, phone.

(Just ask me: The screen of the iPad 2 we bought last March looks sadly blurry next to the new model’s.)

But will the same more-is-better math prevail in HDTVs? I doubt it.

The 4K and Quad HD sets that made scattered appearances at CES in January start out with the same “you want me to replace the set I only bought three years ago?” issue that has helped hold back 3D TV. Then they plow into two other problems.

(4K resolution usually means 4,096 by 3,012 pixels, but the vertical resolution may vary with particular releases. Quad HD is, logically enough, four 1,920-by-1,080-pixel 1080p HD frames: 3,840 by 2,160 pixels. For the sake of brevity, I’ll use “4K” to refer to all these related standards.)

As with 3D, there’s a lack of content–not from a shortage of material, but because no easy way exists to bring it to your living room.

The 4K format has a stamp of approval from Hollywood as a digital upgrade from film, but 4K video takes up an inordinate amount of room. Digital Cinema Initiatives, a joint venture among major movie studios, mandates (PDF) 307 million bits per second of bandwidth for the combination of 4K video, 16-channel audio and subtitles.

That can work for a movie theater. But when 100 Mbps home Internet connections are vanishingly rare in homes, that’s a non-starter for consumer video.

Compressed formats can lower that bit rate, at the cost of greater processing power needed to render the footage. In July of 2010, YouTube announced support for 4K video–but a 2009-vintage Mac kept dropping frames in three sample clips.

Off the Internet, broadcast support for 4K is out of the question, and cable and satellite services would struggle to scrape together capacity for the format.

With the right compression, however, Blu-ray discs could store 4K movies. And Sony announced one player at CES that will upconvert video to 4K.

(Glasses-free 3D TVs require quad-HD resolution. But as I mentioned, 3D has issues of its own.)

That leaves 4K’s other problem: On most common screen sizes, you may not notice the extra resolution.

Go back to the idea behind Apple’s “Retina display” talking point: When a screen becomes sufficiently sharp, you can no longer distinguish individual pixels.

There’s math behind this sales pitch, and over a year ago The Unofficial Apple Weblog’s Richard Gaywood broke it down to determine what resolution an iPad-sized touchscreen would need to quality as a Retina display. Factoring in viewing ranges for a tablet computer, he correctly calculated that 2,048 by 1,536 would work.

He included the formula he used for this calculation, plus a later Google Docs spreadsheet showing his work and a helpful equation form on the WolframAlpha site that you can use yourself. Divide a display’s height in inches by its vertical resolution in pixels (the PX CALC site can compute its height from its resolution and diagonal screen size), plug that pixel-spacing number in between the equals sign and “/2d” on that WolframAlpha page, and its “Solution” line will report the minimum distance at individual pixels vanish from 20/20 sight.

In my home, we have a 40-inch 1080p HDTV in our living room. And by this math, playing a Blu-ray disc or other 1080p source on our set earns it Retina display status as long as we sit about five feet away. Even lower-resolution 720p video from Internet and over-the-air broadcasts qualifies for that honor when viewed from eight feet away. That happens to be the closest our couch gets to the set–and it matches my own viewing experience.

So from where I sit, tablet vendors should keep working to upgrade their screen resolutions. But TV manufacturers can probably find better outlets for their talents.

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  • Michael


    please do your homework before wasting your time writing an ignorant article –

    All Satellite providers are preapring for 4K

    TV execs are bullish in 4K –


    ESPN is building a billion dollar facility for 4K broadcasting — unveiling in 2014 



  • http://robpegoraro.com Rob Pegoraro

    Thanks for the input. I’m puzzled by the way you tout those stories as evidence for your optimism, because they don’t quite live up to your descriptions. 

    The first one only says DirecTV–which doesn’t even count as “All Satellite providers” in the U.S., much less the world–thinks 4K could be a good product in four to five years. The second one quotes one panel at a conference, which–having spoken on enough panels in my time, doesn’t count as an industry consensus. (I would have liked to attend, because it sounded like an interesting discussion, but I was out of town for SXSW.) And the third story you link to only reports that ESPN is building a new production facility, with a vague wink-and-nudge suggestion that it might support 4K.For the sake of the shareholders involved, I certainly hope that DirecTV and ESPN aren’t about to bet a large sum of money on 4K. In the consumer space, I don’t see it happening anytime soon, quite possibly ever.- RP  

  • Michael


    I agree with your point with respect to said panel discussion, but the collective wisdom of these decision makers are leaning towards 4K ubiquity, as opposed to stationing them themselves in an HD-centric world.

    Is the Sharp VP wrongheaded in his 4K declaration?  http://www.twice.com/article/481186-Sanduski_Sees_Growth_Ahead_For_Big_LCDs.php

  • Jbdc

    The links to the “3D issues” posts don’t return an article.

  • http://robpegoraro.com Rob Pegoraro

    Yes, I would say that my friends at Sharp (really–I’ve known a lot of those folks for a long time) are mistaken to steer the company towards 4K displays. Just banking on over-60-inch TVs seems like a formula for marginalization. Reading between the lines, TWICE’s Greg Tarr also sounds a bit skeptical of this strategy too.

  • http://robpegoraro.com Rob Pegoraro

    That link should be http://blog.ce.org/index.php/2011/09/12/3-d-tv-and-3d-technology/ (it’s right in the draft saved on my computer; not sure what went awry, but we’ll get it fixed). 

    - R