In comments Gregory suggested that a proper test for resolution of 3D systems might involve such things as the perceptibility of really small text. I agree entirely.

And apparently such tests have been done. These are recounted to some extent in the decision by the National Advertising Division of the US Council of Better Business Bureaus.

You can read about one of the small text tests at Dr Soniera’s website. This is based on examining some text within a Blu-ray 3D presentation, which is more or less the way I tend to do things. Dr Soneira’s evidence was adduced in the NAD’s decision to the effect that passive 3D TVs provide full resolution.

The other test was by a ‘clinical research study’ by Drs Martin Banks and Joohwan Kim entitled ‘Spatial Resolution of Temporally and Spatially Interlaced Televisions’. Now it turns out that Dr Banks runs something called the Visual Space Perception Laboratory at the University of California, Berkely. Perhaps I’m misinterpreting, but it’s hard to see Dr Banks’ qualifications as anything other that impressive for conducting this kind of study.

What follows is taken from the NAD’s decision, and is thus filtered through the NAD’s paraphrasing. Here’s what Samsung claimed:

Samsung provided nine separate reports showing that the images delivered by passive 3D televisions were measurably and visibly less detailed than those provided by active 3D televisions. In addition to the Samsung Korea, Intertek and Underwriters Labs (“U.L.”) reports, Samsung provided the report of a clinical research study by Drs. Martin Banks and Joohwan Kim (“Banks report”), and a comparison of Samsung and LG 3D display resolution by Joe Kane (“Kane report”). Samsung also provided published, third-party reports from expert reviewers at Consumers Union, HDTVTest.com, CNET.com, and TrustedReviews.com. All of these reports and reviews, without exception, state that the evaluated passive 3D televisions delivered less detailed 3D images than active 3D televisions (i.e., delivered only a maximum of 540 vertical scan lines to each eye when in 3D mode) but that active 3D delivers 1920x1080p to each eye in 3D mode. All of them attributed the loss of detail with passive 3D to the spatial interlacing method used by passive 3D televisions to display the respective 2D images to each eye, which inarguably cut the source resolution in half.

Focusing on the Banks report:

Samsung’s expert, Dr. Martin Banks, Professor of Vision Science at the University of California at Berkeley, explained that the two half-resolution images created by passive 3D technology are not recombined in the brain to create a full resolution image, as claimed by Dr. Soneira. Dr. Banks’ research demonstrates that the effective human visual resolution of the Samsung active shutter system is equal to the full resolution of the television because both eyes receive information from all the pixels in the television. Dr. Banks’ study shows that LG’s passive 3D approach achieves only half resolution to each eye and that there is no way the binocular image could have more than half resolution vertically. Thus, Dr. Banks concludes, the “effective spatial resolution is higher with the temporally interlaced Samsung television than with the spatially interlaced LG television except at long viewing distance (six times picture height) where the effective resolutions are the same.”

Soneira had a go at Banks’ methodology:

Insofar as Dr. Soneira criticized Dr. Banks’ research by arguing that it utilized “artifical” 3D content, Dr. Banks responded that the “letter acuity test” he used in his study is a worldwide standard for optometrists, ophthalmologists and motor vehicle departments to assess visual acuity. Indeed, he stated that it is much more accurate to use a letter-acuity test, with high contrast lettering of a standard font, to assess display resolution differences because it controls for artifacts that could be inherent to consumer 3D video content. Further, it is a non-biased methodology that removes any potential bias or variability, unlike the Soneira’s testing which relied on the test administrator to select visible text within a consumer video on an ad hoc basis.

Dr. Soneira further criticized Dr. Banks’ research for requiring participants to guess what letter they think they saw after seeing it for 600 msec, Samsung countered that this criticism is unfounded and is based on a lack of understanding of consumer testing methodology. The use of a forced-choice methodology in this study and even shorter durations than 600 msec. is standard in vision science (and other consumer testing). Letter acuity is unaffected by stimulus duration for durations greater than 400-500 msec. According to Dr. Banks, “[b]y forcing subjects to make a response even when they are uncertain, we can eliminate performance differences due to personality variables (i.e., the willingness to make a possible mistake) The issue at hand is the effective resolution of the TVs, not the subject’s willingness to make a response.”

LG responded to the Banks report by noting:

The Banks report, for all of the technological information provided, employed the use of visual acuity charts. While such testing might well be sufficient for visual acuity or other technical scientific discussion, insofar as it is offered for advertising claim substantiation (indeed, for superior picture resolution and 3D picture quality claims), it bears no resemblance to actual 3D content typically viewed by consumers.

It added:

The Banks report relies on a test methodology that has no relation at all to actual 3D content viewed by consumers and did not involve actual 3D TV content but, rather, employed the use of test charts — hardly adequate support for Samsung’s broad claims that its active 3D TVs provide double the resolution and superior picture quality over passive 3D TVs. Moreover, Dr. Banks purportedly found that Samsung had higher 3D TV picture resolution at distances of 1.5 and 3 times picture height — far less than the viewing conditions found in most households, as well as Samsung’s own recommended viewing distances (i.e. three times or more the height of the screen.) Indeed, Dr. Banks’ study failed to test picture resolution at 4.5 times picture height (a closer approximation of normal viewing conditions) and inexplicably jumped from 3 times picture height to the much farther 6 times picture height.

(My bold.) The bolded phrase is irrelevant to the current discussion (I for one tend to the view that LG’s 3D actually provides a slightly ‘superior picture quality’ in 3D mode, all things considered.)

NAD was persuaded by LG’s claims. I am not.

As I have noted elsewhere, one important reason for high definition is to allow you to sit closer to the screen so that it can occupy a larger angle of your vision, when compared to SD. If you are going to invalidate tests which suggest that you get more detail at those closer distances, then why even bother with HD? Of course if you sit far enough back from a 3D TV, any loss of resolution will become imperceptible.

Why Samsung recommends a viewing distance of 3 times the screen height I do not know. LG, with its current range, recommends that a viewing distance of twice the screen diagonal in 3D mode. Consider a 55 inch TV. Three times the screen height (Samsung’s apparent recommendation) is 2.05 metres. Two times the diagonal (LG’s recommendation) is 2.79 metres. To put in another way, LG’s recommended viewing distance is 36% greater than Samsung’s. Perhaps there is a reason for this.

I would note that I’ve just finished reviewing Sony’s Personal 3D Viewer headset. This purports to offer an image equivalent to viewing a 750 inch screen at a range of 20 metres. That’s the same angle of view as watching a 55 inch screen at 1.47 metres.

And that only offers a 720p display!

I have watched a lot of stuff on both active and passive 3D TVs. Fact is, at a range of 2.7 metres the same real world 3D content looks more detailed and somehow whole on my 83.5 inch front projection screen using an active DLP 3D system than it does on a 55 inch passive 3D system. That’s not to say that a Samsung direct view TV of a given size is ‘better’ in an overall 3D sense than an LG set. It is to say that that the vertical resolution as perceived by a real human being on a current model passive TV set is less than that available from a best practice active display.

In reality, I find ludicrous the suggestion that a passive 3D TV somehow offers full vertical resolution. It simply doesn’t.

So, in a rush on Friday I claimed that the new LG TV I was reviewing delivered its 3D signal in a particular way. I should specify my method.

First: an assumption. Necessarily my tests were conducted by providing the TV with a 1080p 2D signal and then using it to convert to 3D, using the side-by-side 3D process, which is the process used with 3D TV broadcasts. This is fully explained here. The assumption is that the TV uses the same line allocation methods with other forms of 3D as it does with this one. So far I’ve seen nothing to make me think otherwise.

So here’s what I did: I created a number of 1,920 by 1,080 still images in which every single horizontal row of pixels was different to the row above. For example, here’s a detail of one called red-blue:

At first glance it looks like a solid purple block. But, in fact, it is a single row of red pixels, with a single row of blue pixels underneath, then a single row of red pixels and so on. Here’s a smaller detail of the same pattern, zoomed in to 300% to make it easier to see the row structure:

(I know, I know, the red lines don’t look red, and the blue lines don’t look blue, but they are. I will post later to prove that your eyes are lying.)

With the TV set to 1:1 pixel mapping, each of those pixel rows occupies on scan line of the TV. When I showed this on the TV — in regular 2D mode — and donned the passive 3D glasses, the picture on the screen was entirely blue to my left eye, and entirely red to my right eye.

Since the top-most row of the test pattern was red, and if we count that row as #1, that means that the left eye sees the even (blue) rows, and the right eye sees the odd (red) rows.

What I also needed was a comparison test pattern. This one is identical to the first one, except that the line sequence is red, blue, red … only for the left half of it. On the right half it is reversed: blue, red, blue … Here is a detail, taken from the centre top of the actual pattern, and zoomed in for clarity:

Showing this pattern in regular 2D mode on the TV, and looking at it with the 3D glasses, to the left eye the left half of the screen is full blue (same as the first pattern), and (still with the left eye) the right half is full red (since the line sequence is reversed here). Through the right lens the left half of the screen is red, and the right half is blue.

Now here’s the thing: if we switch the TV to side-by-side 3D mode, the difference we see between these two test patterns will tell us what’s going on as far as which source lines are being used to create the output picture lines for the two eyes. If, for example, every odd line is discarded for both eyes, then we’d expect to see differences between the two different test patterns in 3D mode. Likewise if all the odd lines are discarded for one of the eyes and all the even ones for the other eye, then there must be differences between the two test patterns in 3D mode.

So what do we see? Well, here’s a photo of the screen of the TV showing the first test pattern. No glasses were used, so this is showing both left and right eye views simultaneously:

And here’s a photo under the same circumstances of the other test pattern (where the lines are reversed in the right hand view):

See any difference? Neither do I.

More importantly, there is no difference wearing 3D glasses. There is no difference between the left and right eye only views and these ones except for one thing: the ‘Pause’ and the text at the bottom right left were visible only in the left eye view since they came from the left hand part of the source. There are no differences regardless of other picture processing settings I make — in particular, switching TruMotion on and off.

Conclusion: in 3D mode each display line (remember, there are only 540 display lines for each eye) is created from a matched pair of odd and even display lines from the source for each eye. Since those odd and even display lines are always red for one and blue for the other, the result is always purple.

How those display lines are merged is perhaps unimportant. But two possibilities are rapid alternation — at far too high a rate to be perceptible — or electronically prior to display. I doubt that either choice makes any practical difference.

I repeated this test two more times, with alternating lines of red and green, and of blue and green. The result was the same: no difference between the two versions. It is clear that whatever has gone before, LG now uses a system in which all the source lines are used in 3D display. But whether the way in which they are used offers something like full resolution is another matter, which I address here.

(A note on colour: the photos of the TV came out quite a bit darker than this looked on the screen. I toyed with lightening the results, but thought the minimum of tampering better. Both pics were taken with the same manual aperture and shutter speed settings, with white balance set to ‘sunlight’. The only processing I did was to rotate clockwise by 1.57°, crop and resize to fit this page.)