The 4K Debate…”technical”

Categories: 4K filming 3 Comments

4K

“4K is FOUR TIMES the resolution of High Definition!” …really???

I do wish people, some of whom should know better, would stop quoting the marketing hype by saying that 4K or rather QFHD (Quad Full HD: 3840×2160 pixels), is four times the resolution of Full HD (1920×1080 pixels) when clearly it is TWO times the resolution (on each axis) and therefore FOUR times the NUMBER of pixels (X x Y axis, image width x height) on the sensor.
Resolution, in my 40+ years experience, has always been a linear measurement of lpmm (lines per mm) or, more accurately, lppmm (line pairs per mm: you need one white & one black line to see the difference).
In the case of digital sensors, we’re talking about how many pixels (image sampling points) are potentially available on a given axis. I say ‘potentially’ as other factors such as AA filters on the sensors, image processing/codecs and the resolving power of the lenses in use may be the limiting factors, regarding actual achievable image resolution, rather than the sensors native pixel count.
Hence QFHD (16:9 3840×2160) with 3840 pixels image width is twice the (sensor) resolution of Full HD (16:9 1920×1080 pixels) with 1920 pixels image width …simple mathematics: 3840/1920 = 2.
4K or, rather, Cinema 4K (17:9 4096×2160 pixels) at 4096 image width might also be said to be 2.133333333~ times the image width resolution of Full HD (4096/1920) but still two times on the height axis (2160/1080).
Using Bob Miano’s received ‘logic’ we might also claim that Full HD with an image pixel count of 2,073,600 pixels (1920×1080) is 2.25 times the resolution of HD at 921,600 pixels (1280×720) …that’s not a claim I ever recall hearing and, of course, the actual figure should be that Full HD is 1.5 times the resolution of HD (1920/1280) …a 50% increase, not 125%.
As for “capturing in 4K will allow you to “zoom in” to the footage in post” …yes, up to a 2x crop (onto a Full HD timeline), any more than that and you’ll be looking at an image with LESS than Full HD resolution. Try going in by the implied 4x crop and you’ll be looking at a 960×540 pixel image …less than (PAL) SD!
I can understand the marketing boys at Panasonic, and others, shouting the “4K is 4 times the resolution of HD” nonsense but ‘professional’ users might be better off not to over hype the possibilities and risk disappointing their customers …well at least until we get ’8K’ cameras that CAN shoot at 4x Full HD (7680×4320 pixels)!…?
Personally, having been happily using the GH3 for over a year, I’m just looking forward to exploring the additional possibilities of what I’ll be able to do, in both QFHD and Full HD, when my (pre-ordered) GH4 turns up

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3 comments on this post

  1. Chris Gibbs says:

    Hi Philip,

    Thanks for the insights, that makes perfect sense, I can understand your frustrations with the marketing hype!

    Same goes for us in the stills world, we hear about “lens equivalence” and most of it is “marketing double-talk” also. That 12-35 f/2.8 is for all intents & purposes a 12-35 f/5.6 and that’s “THE LOOK “you will get from it, BUT, if you also take into account that your working distance is actually twice that of a 35mm sensor it gets even more convoluted.

    In short, there is no way shape or form that the 12-35 f/2.8 M4/3 approximates the look of a 24-70 f/2.8 on a 24x36mm sensor. Is it better or worse? That’s also irrelevant. The question should be. “Is it more appropriate for the subject matter I shoot?”

    Apologies for going off-topic, but as you have found frustration with “file size marketing” we photographers have with with “sensor size marketing.”

    Chris

  2. Ryan Forte says:

    You forgot to mention something very important! The 4k televisions are capable of reproducing 10bit color space which looks spectacular! I’ve spent the last year making and mastering our film moonshine kingdom in Ultra HD & Cinema 4k in 10 bit color along with 4k studios in Cali where they scan 35mm film to 4k and it is all stunning. This will be the last tech jump for consumers and home entertainment cause 8k will only have use with a giant screen and I mean giant!! Definitely not for 16×9. I know everyone is ready to jump on the hating band wagon, but its not only the increase of resolution its more color which any professional in the film industry will tell you is a breath of fresh air!

  3. John Norton says:

    “As for “capturing in 4K will allow you to “zoom in” to the footage in post” …yes, up to a 2x crop (onto a Full HD timeline), any more than that and you’ll be looking at an image with LESS than Full HD resolution.”

    Hi Philip, thanks for your very informative info on GH4 crop factors. I wonder if you could help with the following crop related issue …

    Example, footage shot in 4K, put on timeline, some section of it zoomed in/cropped to 2x max. If this edited video clip is output/rendered as 1080 x 1920 FHD, does the cropped part of the outputted video now have poorer quality (maybe SD quality equivalent) than if the video clip was originally shot in 1080 x 1920 FHD, not cropped/zoomed in and outputted as 1080 x 1920 FHD.

    thanks in advance,

    JN

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