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Archive 2016 · Questions about pixel density and viewing distance...

  
 
cameron12x
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p.1 #1 · p.1 #1 · Questions about pixel density and viewing distance...


First, I'm not sure if this is the best forum to pose this topic. Apologies in advance if it isn't.

I'm in the process of defining a Home Theater system for my condo in a small 13' x 13' x 9' downstairs finished room. I anticipate viewing my video monitor from 7' to 9' away. The audio description of my proposed system is separate from this topic. I anticipate having many digitized "slide shows" on my TV monitor (TBD).

In general, I believe that most agree that we get enough resolution from 4-6mp digital image files to equal usable detail which existed in 35mm film. Obviously, we can do much better than that today with 35mm format vDSLRs (Nikon = 36mp, Canon = 50mp). Even more resolution is on the way. But I digress.

A few 4K video questions to ponder. First, how well will it render digital still images? (Slide shows are at least one useful application.) Obviously, viewing distance matters. I'll come to that later. (How accurate is the chart below?)

Consider the native 4K resolution: 3840 x 2160 pixels in a 16:9 aspect ratio. If we truncate the horizontal resolution to 3240 pixels (to accommodate the standard 3:2 aspect ratio for still images) we arrive at approximately 7mp of image data (3240 x 2160). Note that 1080p resolution when scaled to a 3:2 aspect ratio only produces about 1.75mp of image data. A huge difference and far less data that is required to effectively render 35mm still images.

For those mathematically inclined, lets take a look at PPI (pixel-per-inch) resolution and monitor size. Let's first arbitrarily assume 72 PPI is a desired goal. (Question: how will a viewing distance of approximately 8' affect the arbitrary 72 PPI goal?) And what is the minimum monitor size needed to achieve this? (That's the somewhat incomplete exercise which follows.)

If we work from this arbitrary starting point, we have (3240/72) which yields 45" for the horizontal dimension. The 3:2 aspect ratio then gives us 30" for the vertical dimension. Using the Pythagorean theorem yields approximately 54" for the diagonal dimension. That dovetails nicely with the 55" sweet spot for TV monitors today. However, that omits the necessary re-scaling back to the 16:9 aspect ratio, since TV sets/monitors do not render in 3:2 format.

So, using 30" as a fixed vertical dimension and re-scaling the horizontal (longer) dimension back to the 16:9 aspect ratio, we get dimensions of 30" x 53". From this, again using the Pythagorean theorem we derive a diagonal dimension of about 61". So, does it then follow that in order to effectively display "35mm digital images" that a 4K monitor should minimally be a 60" or 65" unit? (Assuming the above parameters.)

All things being equal I know that color gamut and contrast trump resolution, but resolution and viewing distance DO matter. So, another question to ponder: How does a viewing distance of approximately 8' factor into all of the above? Any opinions? (I know, this can dovetail into broader topics.)

Thanks in advance for your critical thinking!







May 03, 2016 at 09:55 PM
justruss
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p.1 #2 · p.1 #2 · Questions about pixel density and viewing distance...


A lot of those charts are more theoretical ballpark figures-- rather than experimental results.

That is to say they base those results off of assumed "perfect vision" (of which there is no such thing, only a distribution), while considering only a very basic view of resolution.

I don't have better than 20/20 as far as I know, and yet I have picked out differences between 4K and 1080p, on 48" screens, from as far back as 10 feet or so; the chart would suggest that the screen need be 70-80 inches to distinguish this.

It would be expensive, but I'd trust these charts more if they were based on experimental data, in a controlled setting, showing actual content on actual TVs.

Until that happens-- I'll keep going bigger and higher resolution until I don't see improvements (in everything from pure resolution, to noise, to motion, to DR, to ..... )



May 04, 2016 at 03:22 AM
cameron12x
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p.1 #3 · p.1 #3 · Questions about pixel density and viewing distance...


I completely agree. These are experimental and calculated numbers.

And I truly wonder how accurate that subject-distance chart is.

But are my assumptions and calculations in the ballpark for displaying still photo images?



May 04, 2016 at 05:46 AM
KSgal
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p.1 #4 · p.1 #4 · Questions about pixel density and viewing distance...


Ok, my head hurts. What is the goal you are going for? Why not jog down to Walmart or BestBuy and just check out the screens they have from different viewing distances and pick one you like?

Bet you can take a usb thumb drive and plug it in or plug your camera with images on it in and see what it looks like. bring the cables and tell them that is what you are going to do and you can have different resolution and/or video's on the card and check it out.

As I have easily printed 20% of a file image from a 15mp camera to a 20x30 print, I'm pretty sure that about any camera with 15mp or more is going to be fine.

I have a 37" screen at about 10 feet, so the point is pretty moot to me.



May 04, 2016 at 10:29 AM
cameron12x
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p.1 #5 · p.1 #5 · Questions about pixel density and viewing distance...


It hurt my head a bit composing the initial post, believe me!

I looked at a 60" LG OLED display today, and it was gorgeous.

Just an intellectual excercise, for those who might be so inclined to follow-up on it further.



May 04, 2016 at 05:14 PM
KSgal
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p.1 #6 · p.1 #6 · Questions about pixel density and viewing distance...


Well, when I win the lottery, I'll come back here after buying a 70" TV and let you know what I have concluded.


May 05, 2016 at 12:57 PM
cameron12x
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p.1 #7 · p.1 #7 · Questions about pixel density and viewing distance...


The new Vizio 65" P model is an intriguing value at $2K.

I will definitely be checking out that unit. The only major issue, as I see it, is up-sampling from 720 (or lower res) content. Off-angle viewing is not the best, either. Otherwise, it seems like an excellent value.

The Chromecast navigation is novel, perhaps disruptive to the industry as a UI, but might be buggy out of the gate.



May 05, 2016 at 03:39 PM
cameron12x
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p.1 #8 · p.1 #8 · Questions about pixel density and viewing distance...


A great discussion here on some of these issues:

http://www.avsforum.com/forum/68-digital-projectors-under-3-000-usd-msrp/2389706-seating-distance-720-1080-uhd-visual-acuity.html



May 08, 2016 at 09:03 AM
RustyBug
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p.1 #9 · p.1 #9 · Questions about pixel density and viewing distance...


What size photo files? Are you keeping them native or filling the screen?


May 08, 2016 at 09:28 AM
cameron12x
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p.1 #10 · p.1 #10 · Questions about pixel density and viewing distance...


Truncating the long (16) horizontal dimension of the 16:9 format to meet the standard full-frame 3:2 aspect ratio of 35mm and vDSLRs.

That's about 7mp of image data.



May 08, 2016 at 05:21 PM





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