Warning: NSFW
Walter Volpatto, Sr. Colorist, Picture Shop, argues that HDR causes discomfort because, unlike in real life where the scene before us occupies our entire field of view, we’re watching TV in a dark room where the picture occupies a much smaller field of view, forcing our pupils to open up, making the image look disturbingly bright. He notes that grading on Sony’s Wall caused no eyestrain because it covered all of his peripheral vision.
We’ve never experienced any discomfort while watching HDR content, but just the same, last night, we tried sitting around 7 feet from a 65” QD-OLED to discover whether it was any less comfortable than sitting 4 feet away (1.5X picture height), where the picture occupies a greater field of view. We did find the closer distance to be more comfortable, perhaps because the experience just felt a whole lot more immersive, but in neither instance did we feel any eyestrain or fatigue.
It might seem reasonable to conclude that Mr. Volpatto is correct about our eyes adapting to the surround illumination + the brightness of the television when seated several picture heights from a display but we’re not at all convinced that a display the size of Sony’s Wall is either necessary or desirable: when seated in a dark room at the optimal viewing distance (1.5X PH for 4K) from a UHD TV, the picture should be the deciding factor determining pupil adaptation, not the ambient light (see Controlling Field, Pupillometey of HDR Video Viewing, below). Not only that, but you’ve got to be pretty far away from the Wall in order not to see the individual pixels – the FOV remains constant; only the viewing distance changes. Volpatto writes:
“The contrast ratio in this image is 45.000/4= 11000/1 (at least) and I have no issue in looking at it.”
“This is the point: if you look at the outdoor real life through a window where it is dark indoors, you will feel discomfort in real life. That is when you see “high dynamic range” images but at the same time you will have the average of the scene being on the dark side and that will force your eyes to open the iris.”
“The issue with a HDR TV is not the max brightness, NOR the high dynamic range you can put on it, but the relationship between the peak highlights and the average of the scene INCLUDING your surrounding.”
Let’s do a thought experiment.
“Let’s say that you have an ideal camera, an ideal wall, and an ideal monitor, all of which can capture and perfectly reproduce 15,000 nits and you’re shooting the scene represented above.”
“Now, if you look at that scene with a 30-inch 15000 nit monitor at the recommended distance, with the recommended light surrounding (that is even lower than 709… *sigh*). you will not be able to look at it. period. too much of the image is dark, forcing your eyes to open and the TV will look stupidly bright.”
“Now, imagine a “wall” 15.000 nits that covers all the peripheral view of your eyes: your eyes will behave simply put like in real life and you will be able to look at it without any particular problem.”
“Because the average is so important, building an image where the average of the intended content (the 11/12 stops of he actual subject matter) is relatively low and then push the highlights in HDR very high, will only achieve to disturb your vision and nothing else, compounded with it, there is the size of the screen and the idea that we should look at HDR displays in complete darkness: it is equivalent to experience life thru a window in a dark room all the time.” [text edited slightly for clarity]
The following excerpt is from Pupillometry of HDR Video Viewing by Scott Daly, Evan Gitterman and Grant Mulliken, a paper that addresses light adaptation and discomfort and introduces the concept of controlling field.
Controlling Field
“Pupil size adaptation is primarily affected by white and green light, and the portion of light in the visual field that most affects the pupil size is properly termed the controlling field (as opposed to adapting field). This generally refers to a brighter region than the rest of the visual field, and in most experiments, it is a luminous disc against a darker background. The controlling field size can be as small as 1 degree.”
“Since the display is generally brighter than the surround, the pupil size will be controlled by the displayed imagery. This likelihood increases as the field of view (FOV) of the display has been increasing over time (technically at 65 degrees for the new UHD formats). So, the controlling field will be within the image content. It is entirely within reason that content may have a bright region as small as 0.4 degrees, and as large as 25 degrees.”
The following excerpts are from Subjective Quality Evaluation of High Dynamic Range Video and Display for Future TV, a study that lends credence to the well-documented observation that increased FOV contributes significantly to quality of experience:
“The FOV is important for HDR display because of the glare due to the optics of the eye and the long tails of its point spread function. Also, other issues are found, such as light adaptation, anchoring, and eye movement aspects that favor a larger FOV presentation.”
“The results have also shown that quality differences of brighter HDR content are visually recognized as independent from the viewing distances studied. Nevertheless, this does not mean that viewers had the same experience at 1.5 m than at 2.7 m, as the FOV is known to impact immersiveness, which is one of the factors that contribute to quality of experience. Considering the different FOV aspects, the closer viewing distance is expected to provide a better experience.” Subjective Quality Evaluation of High Dynamic Range Video and Display for Future TV, by Philippe Hanhart, Pavel Korshunov, Touradj Ebrahimi, Yvonne Thomas, and Hans Hoffmann
It must be remarked that ambient light was not considered as a variable in the design of the above study.
Steve Shaw, founder of the display calibration software company Light Illusion, maintains that a FOV of around 45° is required to benefit from HDR:
“Further, with the relatively small size of TVs, combined with the standard viewing distance – 3m or so – the whole TV screen is within the high-acuity, central angle of view of the human eye (5° to 15°), meaning the human visual system cannot respond independently to different areas of brightness – being stuck within a state of full adaptation, so the viewer is only able to use the static dynamic range of the human eye.”
“To actually gain benefit from the concept of HDR the actual viewing angle the display would need to occupy would be in the order of 45°, which with an average large TV of 55″ would means [sic] sitting just 65″ from the screen.” Steve Shaw, CEO, Light Illusion
For a 4K UHD TV, the FOV is 65 degrees when seated at the design viewing distance of 1.6H.
Lastly, the following is from the International Telecommunications Union Report ITU-R BT.2246-8 – which states what many in the industry still fail to understand – which is that one of the chief goals of UHD TV was to offer a wider field of view than was possible with HDTV:
Television has built its history on the fundamental desire of human beings to extend their audiovisual senses spatially and temporally. HDTV is one of the great achievements of television. People in many countries are now enjoying the benefits of HDTV, and people in the rest of the world will soon benefit in the near future.
The definition of HDTV, described in Report ITU-R BT.801 The present state of high-definition television, is as follows:
A high-definition system is a system designed to allow viewing at about three times the picture height, such that the system is virtually, or nearly, transparent to the quality of portrayal that would have been perceived in the original scene or performance by a discerning viewer with normal visual acuity. Such factors include improved motion portrayal and improved perception of depth.
The attainment of this goal is limited in some aspects; e.g. the field of view of HDTV is only 30 arc- degrees. Our natural desire to overcome such limitations has led us to the concept of UHDTV:
UHDTV is a television application that is intended to provide viewers with an enhanced visual experience primarily by offering a wide field of view that virtually covers all of the human visual field with appropriate sizes of screens relevant to usage at home and in public places.
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