Werner Asks If We Really Need UltraHD?

By Raverstead
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Ken Werner of Nutmeg Consultants has been involved with Latin Display for some years, but a last minute problem with his visa meant that he couldn’t attend, so our own Bob Raikes presented his talks.

The first focused on the question of whether we really need UltraHD displays. He looked at how acuity is measured using charts rather than full images. He also looked at the issues of vernier acuity (the human perception system is incredibly good at judging when fine lines are just slightly offset from each other – and that’s the kind of effect you see in the “jaggies” of font rendering on lower resolution displays).

Werner also pointed out, on the basis of research from Pixelworks, that effectively a digital display (or more precisely the camera/display combination) is a sampling system. If you imagine a vertical dark line that is slowly moving horizontally, at one point, the line will align directly with a pixel, giving a clean edge. However, if there is a small shift by the next frame, the sampling effect means that the edge will be grey rather than black. In textures in motion, this artefact can be distracting (he suggested a kilt pattern waving in the breeze in Braveheart!). Having more samples reduces this problem.

He quoted Pixelworks in saying that “When the sampling-phase effects are taken into account, the perceivable pixel density limit increases from 60 ppd to nearly 90 ppd”. PPD is pixels per degree, equivalent to half as many “cycles per degree”. 20/20 vision acuity is around 60 ppd/30 cpd, (although 20/10 vision is 120ppd/60cpd). A FullHD 55″ TV at SMPTE viewing distance gives around 62ppd and UltraHD gives 124 ppd.

On this basis Werner believes that UltraHD will give better images even on 55″ sets.

Display Daily Comments

Raikes asked why supersampling is seen as a good idea in audio, but not so often in video? Having said that, the Sony Alpha 7S camera that I’m using makes the most of all of its 12 megapixel sensor to downscale to FullHD, eliminating moir√© and other artefacts.

See the Display Daily guest article from Candice Brown Elliot in this issue for a detailed look at this issue. (BR)