Originally Posted by HoustonHoyaFan
I suspect that we could come to some reasonable approximation of a top end CR number for video displays if we could start from some established scientific baseline. We seem unable as a group to even do that.
I suggest we start with 2 common "facts" in the HVS community:
1) The retinal ganglion cells can output a luminance range of <200:1 per precept (visual frame). The CW in HVS research is ~100:1.
2) Luminance adaption (contrast gain) can occur in as little as ~1/10 sec.
If we put those numbers together with the video frame rate of 1/60 sec maybe some like Darin can come up with a number that most of us thinks makes sense.
One thing I am not clear about is whether you consider something being shown at 60 frames per second to be 60 simultaneous frames with each limited to 200:1 without eye movement, or if just the motion in the images themselves negates the thing about simultaneous frames. For instance, the HVS is using motion as one of the clues to make out detail. As an example, if one frame had 250:1 and things outside 200:1 were crushed and the next frame had the exact same levels, except with the brightest and darkest parts shifted laterally, is it your claim that a person would not be able to perceive that motion at both ends. Again, in this case both images have the same CR with the same peak and the same valley, but just in different spots.
It also isn't clear to me if your position is that the ganglion cells could not report anything different for a 200:1 image than if it was changed to 20k:1 by lowering the darkest item. I don't see anything that indicates that the ganglion cells couldn't report something smaller than is coming off the screen. For example, output 100:1 even though the image is 200:1, but would report 200:1 if the image were 20k:1. Do you see anything that makes that clear? If there is 4% washout from a bright object to the darker part of the image, then it sure looks like they could report less than is coming off the screen and still have room to report a higher number if the CR coming off the screen increased significantly.
Originally Posted by GlenC
How did the topic of this thread get turned into a discussion about the condition where the eye is capable of seeing a "MAXIMUM CR" ONLY?
Seems to me it is more informative to discuss all the variable parameters that limit CR range.
Obviously, there could be a difference in seeing high CR dark detail in a scene, if the bright area is 3" in diameter and 3' in diameter.
While it is interesting to consider different cases where we are more limited and less limited, this thread was about the upper limit at once or in one image. If a person says that people can't see anything beyond x:1 and it turns out we can under some conditions (but that there are also conditions where we can't) then they are wrong if they don't specify any conditions and make it out that it is for all conditions. And if they are teaching ISF courses and making people think that images don't need any more than 200:1 (or 300:1 or whatever it is) at once because we couldn't see improvements beyond that, then that is unfortunate.
Again, if a person wants to say that under y conditions we can't see beyond x:1, then that is fine (if it is true). But a test that uses images that limit our vision more than other images do doesn't prove an upper limit and the result should not be claimed as an upper limit. I bet I could come up with images where you couldn't tell the difference between 20:1 and 20k:1, but I wouldn't claim 20:1 as the limit.