419 replies to this topic

[alanh]

This table which uses the acuity of the average human has been removed by the author and stored.

AlanH

Edited by alanh, 25 March 2013 - 05:05 PM.

[Owen]

I would like to stress that these recommended viewing distances represent the ABSOLUTE MAXIMUM you should use to be able to fully resolve the resolutions listed.
Based on these figures, only 1080p is able to provide better then the MINIMUM viewing angle required for a cinema experience of 26 degrees.
I have to say that I find these recommendations VERY conservative, and much closer viewing distances can easily be used with good quality displays and replay systems. And that’s a good thing, as home cinema would be imposable at this point in time otherwise.
1080i HD video can be easily viewed from less then 4 times screen hight on a 1080i or p display, and even PAL DVD’s of 720x576 resolution properly upscaled to 1080i look very good at 4 times screen hight.
Note that upscaling does not increase real resolution, but it does make a substantial improvement in apparent resolution.

So, if you have a display of sufficient resolution and quality, combined with top quality replay equipment like a HTPC, you can disregard the above viewing distance recommendations and use much closer distances to provide a true cinema experience.

Regards,

Owen

[:)]

Well alanh I for one think your pretty spot on here. We view our 37" plasma from between 2-3m depending of where you sit in the lounge room  which is what it works out for 576i - 1080i given your calculation. Really think this is perfect for  for SD and HD viewing with our display in our room.

This is about the first reasonable/realistic guide I've seen for viewing distance especially when your talking plasmas etc.

I think the other viewing guides often qoutes are more for larger displays - projectors and the like and a waste of time really for panel displays giving ridiculous distances of 1m-1.5m or so !

Owen I'm sure your going to say you can't resolve HD at those distances but think in the end people are going to view their displays at whatever distance they feel comfortable.

[Owen]

Obviously  people will want to use whatever viewing distance they feel works for them. However, if that  be the case, why do they need a guide?
The point of my post was to raise the bar on people’s expectations, and make them aware of what is possible with today’s best technology.
Most displays and replay systems are not up to the task, but some are.
We should strive to achieve the minimum THX compliant viewing angle of 26 degrees which corresponds to about 4 times screen hight.
Obviously a large screen is required if you want to sit more then 2 meters away, and  SD Plasma displays are not up to the task, as they have only half the required resolution.

The recommended viewing angle for THX compliance is 36 degrees (about 2.8 times screen hight). There are VERY few, if any displays on the Australian market that can manage that, and top quality HD source is required for good results.
1920x1080 HD was designed to achieve the above goal and provide a true cinema experience in our homes.

Regards,

Owen

P.S.
By the way Alebonau, I like your contented cat.
I would have thought that he would be sad you bought a Plasma, as there is not enough room on top for him to sleep. :blink:

[:)]

Owen, on Apr 2 2005, 03:17 AM, said:

P.S.
By the way Alebonau, I like your contented cat.
I would have thought that he would be sad you bought a Plasma, as there is not enough room on top for him to sleep. :P

<{POST_SNAPBACK}>

actually shes got the best seat in the house !. Most days you'll find her sitting right in the sweet spot on the ottoman 2.2m from screen - a very contented cat indeed !  :blink:

[Santa]

alanh, on Apr 1 2005, 07:54 PM, said:

All,
The following figures relate to getting the most detail from the screen and is based on average good vision 6,6 (20,20).

You should sit with the eye-screen distance slightly greater than this value.
Select the screen resolution and measure the height of the image. Now multiply this height by the quoted value. This will be the distance between the eye and the screen.

1080p  3.2 x
1080i   4.5 x
720p    4.8 x
576p    6.0 x 
480i    10.0 x
432p    8.0 x
432i    11.3 x This is a 16:9 picture displayed on a 4:3 screen. This leaves black bands at the top and bottom of the picture. So the image height is smaller than full screen.

You can test these figures for youself. If you have to go much closer you may need to see an Optician or Opthamologist.

The link below is not yet operational due to the need to .pdf it. So it will come soon.

Calculator including speaker spacing
AlanH

<{POST_SNAPBACK}>

This should more correctly titled "Alan's Recommendations For Eagle-eyed TV Viewing".

They may reflect the "correct" distance from the screen in order to achieve the absolute maximum resolution, but they are, as mentioned by myself and others, suited to smaller displays for TV programme watching, rather than movie watching.

Two important aspects of the presentation of programmes are:

Immersion - including the viewer in the experience.
Defintion - how clear the image is.

In movies (and other programmes shot/directed like movies ... dramas, etc), the immersion is more important than it is in standard TV programming like the news, gameshows, reality tv, etc. For movie-watching, people like me recommend a resolution trade-off, since we are rather limited (pre-HD-DVD) in the source resolution. With a good setup, even high-quality SD looks fine at a distance way under Alan's recommendation... and you dont have to "do an Elvis"* to view it "correctly"!

Alan's figures are fine for maximising the efficiency of examination of the minutia of every nuance given by the presenter's face, but dont give anywhere near the field-of-view recommended for the  authentic movie experience.

PS: Why the wierd collection of figures? 480p and 432i, but no 576i???

_________________________________
*"Leave the building"  :blink:

[Owen]

Santa, on Apr 2 2005, 01:32 PM, said:

They may reflect the "correct" distance from the screen in order to achieve the absolute maximum resolution,

<{POST_SNAPBACK}>

Hardly, at the distances quoted, you would be hard pressed to see the full resolution of the image, so they should be considered the ABSOLUTE MAXIMUM distances that you can use and still be able to actually see full resolution.
Sure many displays will look better at these distances as the defects in the source and the display will be hidden.
If you sit fare enough away, even a crap display or source looks good.  :blink:


Regards,

Owen

[alanh]

Owen,
Is there a website for the THX standards?
The angles quoted are the for picture width, height or diagonal. I have used picture height because it is not affected by the aspect ratio.

6,6 ("20,20") vision is the bottom line of the eyesight chart. This corresponds to 1/60 of a degree. I have based this to be the size of a pixel.

I have used a reduction of resolution to 70.7% for interlace. This could be greater depending on the persistance of the display.

When the PDF is posted soon, You also have a sound angle of +/-30 degrees between the listener and the left and right speakers respectively. The front and rear speakers should form a square. The centre speaker is obviously under or over the centre of the screen. The subbie can be anywhere in the room.

The other interesting vision thing, is that if the eye movement muscles are paralysed, the ratio of 16:9 is in the same ratio as the angles which can be seen in each direction by the average eye!

In conclusion if your long distance eyesight is worse than 6,6 then you will have to sit closer to see this detail. If the display resolution is not as good then you will wish to sit closer. The arbiter is the eyesight test!

Note these figures are for any display, including analog picture tubes. If the tube is old it cannot display the resolutions given.


AlanH

[Santa]

I'd imagine the website would be thx.com, and that like everywhere these days, the standard would available ... for a price.

The SMPTE Engineering Guideline EG 18-1989 includes their usual recommendations, including that the horizontal subtended angle created by a viewer's line of sight to the left edge and right edge of the screen be not less than 30 degrees.

Personally, I use and recommend:

HomeCinema (big screen) Movies : Subtended Angle ~ 33 degrees.
16:9 TV (standard WS SD TV) Normal TV : Subtended Angle ~ 15-20 degrees.
4:3 TV (standard 4:3 SD TV) 4:3 programmes: Subtended Angle <15 degrees.

________________________________________________
Note: The 16:9 and 4:3 are from memory/off the top of my head.
I did run a thread about this some months back, where I think I outlined the actual values...

[ChrisM]

Resolution is a very tricky thing.  You have the number of pixels on the screen, the spacing between the pixels (i.e. SDE), the actual "photographic" resolution of the source material, the screen contrast, the contrast in the source material, the viewer's eyesight and compression/scaling artifacts etc.

In reality the ideal viewing distance is different for each person, display and program.  basing it simply on the number of display pixels is always going to be a little bit flawed.

The technical ideal of motion picture systems is to create a totally lifelike image that looks like the view from a window.  But in reality people are quite content (and sometimes prefer) to view softer pictures that exhibit temporal artifacts, like the 24 fps judder associated with film, in exchange for an immersive experience.

Alanh's guide is a well reasoned one, but that doesn't mean you can't go bigger if you want to.

With regard to speakers, I think it's more important to keep the speakers out of corners and away from walls.  IMO early reflections have more effect than critical speaker spacing.

[Owen]

Information on THX and other cinema standards is included here.

http://www.myhomethe...ancemetric.html

This guide also includes distance recommendations bases on visual acuity.

Before I found this guide, I did tests on my own visual acuity using a 1600x1200 TFT display and various 1600x1200 test patterns.
My vision is average, and I can read the second smallest text line on an eyesight test chart.
I find it interesting that the results of my tests corresponded almost exactly with the linked calculator.
I posted about this in this previous thread.

http://www.dtvforum....1&hl=resolution


Regards,

Owen

[Santa]

Ok, again I refer to the Definitive Thread on this subject!

[RodN]

I've done a lot of personal experimentation with this on my Z2 projector. I ended up enjoying somewhere around 2.5 to 3 times screen width the most.  With that in mind I would support Owens point that these distances to me feel like the MAXIMUM distance you would want to sit back for a real 'movie like' experience.

I've also done a lot of looking at what they do in the theatres, no (back row) theatre I've been too has been longer than 3 times width with everything much closer!

Maybe there should be 'movie' vs 'tv' distances as Santa suggests.

[Billy Two Hats]

ChrisM, on Apr 2 2005, 10:48 PM, said:

~
The technical ideal of motion picture systems is to create a totally lifelike image that looks like the view from a window.  But in reality people are quite content (and sometimes prefer) to view softer pictures that exhibit temporal artifacts, like the 24 fps judder associated with film, in exchange for an immersive experience.
~

<{POST_SNAPBACK}>

Makes you wonder why they do not make a plasma that does 72hz with 3:3 pull down?

[Owen]

Because changing the refresh rate does not increase the frame rate.
Repeating frames does not improve motion.

Owen

[ChrisM]

Also, 576i 50Hz transfers of 24fps movies are done at 25fps, so it would need to be 75Hz.  However there's no real advantage in faster refresh, except for DLP, where faster refresh = less RBE.

[alanh]

All,
I have added the Viewing Distance Calculator results using the link.

AlanH

[alanh]

All,
I have added the Viewing Distance Calculator results using the link.

Plasmas Display each picture a usual 6 times. Plasmas are like lots of tiny fluros. They are on or off not dimable. To overcome this they turn on the pixel on each of the 6 scans. If it is very dark it is only switched on once.

The standard cinema projector shows each frame of the film twice. A shutter achieves this. So movement is portrayed at 24 frames/s and the flicker frequency is 48 Hz.

AlanH

[ijd]

alanh, on Apr 5 2005, 03:23 AM, said:

Plasmas Display each picture a usual 6 times. Plasmas are like lots of tiny fluros. They are on or off not dimable. To overcome this they turn on the pixel on each of the 6 scans. If it is very dark it is only switched on once.

Are you implying that all plasmas can only show 6 shades of grey (grey is equal parts R, G and B pixels)???!!! :blink:

Or what was your point? :P

[Santa]

Not buying into that (or trying to decipher the specifics).

BTW: A little OT: however, since I dont think I've got around to pointing out (well, not more than a couple of times) how silly the standard catchcry of CRT-haters is wrt flicker... Many of the "digital-or-death" mob aren't aware that plasma and DLP both rely on flickering even more than CRT!
{OK, that doesn't fit into this thread too well, but I feel better for saying it!  :blink: }

[ChrisM]

Quote

Plasmas Display each picture a usual 6 times. Plasmas are like lots of tiny fluros. They are on or off not dimable. To overcome this they turn on the pixel on each of the 6 scans. If it is very dark it is only switched on once.

Wouldn't it need to be eight times?  And when you say per picture do you mean per frame (i.e. 25Hz) or at 50 Hz?

[alanh]

ChrisM,
This gives you 64 levels of grey or 64 cubed as the number of available colours. The reason it is 6 is that this is the fastest they can make the display go without overheating and needing a massive power supply.

My point is that the brighter the colour the more easily seen is the flicker. So the flicker rate is 150 flashes/second for white. Very dark colours are 25 flashes/second. This flicker will not be obvious.

AlanH

[ChrisM]

alanh, on Apr 6 2005, 03:17 AM, said:

ChrisM,
This gives you 64 levels of grey or 64 cubed as the number of available colours. The reason it is 6 is that this is the fastest they can make the display go without overheating and needing a massive power supply.

My point is that the brighter the colour the more easily seen is the flicker. So the flicker rate is 150 flashes/second for white. Very dark colours are 25 flashes/second. This flicker will not be obvious.

AlanH

<{POST_SNAPBACK}>

My understanding was that plasmas resolve 256 greys/16.7 Million colours, which would require more "flashes".  If 6x is the maximum does that mean it takes a full frame time (25hz) to display those 256 greys?

The reason I raise this is that perhaps it's related to false contouring.  If the screen requires 2 field times to resolve 256 greys then deinterlaced video material will have sections of the picture that can only be rendered with a limited greyscale?  Is this why film material, where the fields align, doesn't exhibit false contouring to the extent that video material does?

I'm sorry if this is a bit OT, but I've never really understood how plasma's work.

[alanh]

Chris,
Any image source which either has a shutter or is progressively scanned is then split into two fields for transmission. On reception in the plasma case the image is stored in a frame store. This can be read sequentially or at half the speed if it scans half the rows of the image at the time. It is all realted to the speed of the electronics.

AlanH

[scottylans]

My eyeballs at 2.2 metres from an 86cm (36") CRT HDTV and I can tell you one thing, it's still not big enough :blink: