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# Another Reason Not To Buy A 4K TV Just Yet?

Yahoo Tech

Hi David,

Youâ€™ve pointed out that at normal viewing distances, the current crop of HDTVs already have pixels so small you canâ€™t discern them. You say that adding more pixels (as in the 4K TV sets shown at CES) doesnâ€™t help, so you shouldnot buy a 4K display until the pictures we receive are higher resolution than current full HD.

Youâ€™re right. But, in fact, itâ€™s also a good reason not to go out and mindlessly buy the largest standard HDTV on the market today. First, you should take a rough measure of how far you sit from the TV and compute the optimal size for your space.

Using the formula below (see this article), you can estimate how many pixels you can discern per angular degree at your normal viewing distance. (The distance to the screen should be measured in inches, and the screen resolution in pixels per inch.)

Pixels Per Degree = Distance to Display Ã— Screen Resolution Ã— 0.01745

If the PPD value is greater than 53 (Appleâ€™s estimate for a Retina display) then you can usefully use a larger screen; if itâ€™s smaller than 53, then getting a larger screen means youâ€™ll see individual pixels, which is bad.

You can rearrange the formula and plug in Appleâ€™s Retina display number to compute the screen size corresponding to your threshold, based on how far you normally sit from your HDTV.

Screen Resolution = 53 / (Distance to Display Ã— 0.01745)

I normally sit 100 inches from my TV; so I need a screen resolution of 53 / (100 Ã— 0.01745), which comes out to 30.37 ppi. A full HD picture (1920 Ã— 1080) has 2202.9 pixels on its diagonal. So 72.5 inches (2202.9 / 30.37) is the largest screen I could benefit from. Anything larger and I might start seeing individual pixels.

I would not only be wasting my money but also degrading my experience. I currently have a 46-inch display, and Iâ€™ll likely be keeping it for as long as it lasts.

â€”Duane

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Hi Duane!

I couldnâ€™t have mathed it better myself!

The 4K TV revolution is silly for so many reasons: That thereâ€™s nothing to  watch in 4K (no cable company, no satellite, no disc like Blu-ray can handle that much data). That theyâ€™re crazy expensive.

But you put your finger on the ultimate silliness: That you wonâ€™t even see a difference.

Thanks for making that, um, easier to see!

â€”DP