Or one defines the resolution of the display (and there for the
imager/source/signa), as that resolution it can display with a certain
minimal contrast level. http://www.icdm-sid.org/downloads/idms1.html
Document page 130.
Michelson contrast[edit]
Michelson contrast[6] (also known as the visibility) is commonly used
for patterns where both bright and dark features are equivalent and take
up similar fractions of the area (e.g. sine-wave gratings). The
Michelson contrast is defined as
{\displaystyle {\frac {I_{\mathrm {max} }-I_{\mathrm {min} }}{I_{\mathrm
{max} }+I_{\mathrm {min} }}},} \frac{I_\mathrm{max} -
I_\mathrm{min}}{I_\mathrm{max} + I_\mathrm{min}},
with {\displaystyle I_{\mathrm {max} }} I_{{\mathrm {max}}} and
{\displaystyle I_{\mathrm {min} }} I_{{\mathrm {min}}} representing the
highest and lowest luminance. The denominator represents twice the
average of the maximum and minimum luminances.[7]
This form of contrast is an effective way to quantify contrast for
periodic functions f(x) and is also known as the modulation mf of a
periodic signal f. Modulation quantifies the relative amount by which
the amplitude (or difference) (fmax − fmin)/2 of f stands out from the
average value (or background) (fmax + fmin)/2. In general, mf refers to
the contrast of the periodic signal f relative to its average value. If
mf = 0, then f has no contrast. If two periodic functions f and g have
the same average value, then f has more contrast than g if mf > mg.[8]
https://www.displaydaily.com/display-daily/32947-resolved-no-more-dot-counting
Mark Schubin schreef op 02-07-2017 14:58:
On 7/2/2017 2:11 AM, Manfredi, Albert E wrote:
Visual acuity has to be taken into account. Rule of thumb, ~1 arcmin
of angular separation starts to become noticeable, for humans with
20/20 vision (or less than great vision, but wearing appropriate
spectacles).
We could argue whether absolute visual acuity is as you describe
(called 30 cycles per degree or cpd) or higher or lower. And there
are situations when absolute visual acuity might matter. Watching
television is not one of them. For watching television, what's much
more important is the psychovisual sensation of sharpness, which is
based on both resolution AND contrast.
If you are not familiar with the human contrast-sensitivity function,
these composite images should make its importance clear:
http://bit.ly/angry-neutral
They were created by Aude Oliva at MIT and Philippe G. Schyns at the
University of Glasgow in 1997 and are copyright by them. They are
clearly not high resolution. Combined, they are only 479 x 236
pixels. You should see an angry man on the left and a neutral woman
on the right. Now walk away from your screen. At some point, they
will change places, with the angry man on the right and the neutral
woman on the left.
The images are simple JPEG. They are not animated GIF, and, even if
they were, I have no way to take control of your camera, judge your
distance from the screen, and trigger the animation at the correct
moment. If you prefer, you may print the images; they work just as
well on paper.
What's going on? The images with the angry man on the left are
intended to be seen with their detail at about 6 cpd or higher; the
ones with the angry man on the right are intended to be seen with
their detail at about 2 cpd or lower. The human contrast-sensitivity
function is so strong that, under those conditions, the "wrong" images
completely disappear.
If you graph the modulation-transfer function (MTF) of a system (the
contrast at any given resolution), you come up with a curve heading
downward as resolution increases. According to the image-quality work
of Otto Schade at RCA [Schade, Otto H., "Image Quality : a comparison
of photographic and television systems," RCA Laboratories, 1975,
republished in the SMPTE Journal, volume 96, number 6, June 1987], the
psychovisual sensation of sharpness is proportional to the square of
the area under the curve; according to Erich Heynacher at Zeiss
[Heynacher, Erich, “Ein Bildgütemaß auf der Grundlage der
Übertragungstheorie mit subjektiver Bewertungsskale” [Objective
Image Quality Criteria, based on transformation theory with a
subjective scale], Zeiss Mitteilungen, volume 3, number 1, 1963], it
is the area, not the square. Either way, sharpness is based on
contrast in addition to resolution.
At the NAB Show in April, NHK (the Japan Broadcasting Corporation),
perhaps the world's greatest promoter of higher resolution, showed the
MTF of some near-ideal 8K image sensors. Contrast was 100% at zero
resolution and zero at 8K resolution, as would be expected. At 4K, it
was about 50%, at HD, it was over 80%. Add a lens and real-world
imagery, and the high-resolution MTF goes down even more. Adding
resolution extends the "toe" of the MTF curve, which has very little
area under it; adding contrast (i.e., HDR) raises the "shoulder" of
the MTF curve, greatly increasing the area under it.
Sony took advantage of that low area under the MTF-curve toe when it
introduced HDCAM, dropping horizontal luma resolution from 1920 to
1440; Panasonic went even farther with DVCPRO HD, dropping from 1920
to 1280. Today, with improved technology, both companies' HD
recorders capture a full 1920. Compare the older recordings with the
new, and the difference is perceptible -- but it's not obvious.
Similarly, CBS has a 4K viewing area set up in its Manhattan lab.
There are three 65-inch TV screens, viewable simultaneously from
either three times the picture height or 1.5. All get content shot in
4K. One screen gets an HD downconversion and displays it as HD. The
next gets an HD downconversion and upconverts it to 4K for display.
The third gets 4K and shows it as 4K. CBS has made the setup
available to just about anyone who wants to see the results, so what
I'm about to report is not just my opinion but that of everyone I know
who has seen it, including people from other broadcasters.
At the 3H distance, it's possible to see the difference between the HD
and the 4K displays, but it's not obvious. It's almost impossible to
see any difference between the 4K displays. At 1.5H, it's easier to
see the difference between the HD and the 4K, but it's still not
strong; it's also possible to see the difference between the
upconverted HD and the true 4K, but it's not obvious.
So, all things being equal, sure: let's have 4K. But all things are
not equal, and the increased sharpness going from HD to 4K is not
great. Perceptible, yes; great, no.
The increased sharpness going from SDR to HDR IS great.
TTFN,
Mark
