Originally Posted by trans_lux
Again my point is why use a metric that has absolutely no standard and is open to gross manipulation?
(and this seems like a big if given your posts) that is your point, I agree, it would be nice if there was a standardardized method for measuring sequential contrast. Something with requirements like only measuring without changing settings on the machine, and black/white measurements being made some reasonable time period. I think this would be a nice improvement. It still wouldn't solve the problem of manufacturers measuring in "unusable" modes (caugh Panasonic), but it would stop the bogus measurements where the lamp or manual iris is changed in between.
Further its using values that are so far beyond human vision that it makes no difference.
What are you basing this on? We have hundreds of eye witness reports that (just picking a recent example) the new JVCs with dynamic iris (350,000:1 sequential contrast) are a substantial improvement over the prior years (50,000:1 sequential contrast).
Here's another thread that discusses this:
Here is the salient info:
The range of human vision is (see link for reference) on the order of 10^15, or 1 quadrillion
. Now OK, that includes damaging levels, but if we assume a "usable" range of below the threshold of vision to white paper in sunlight that's 10^10, or about 10 billion. We aren't anywhere close to that.
If we want to "produce" actual black, given a reference light output of 12ftL, we still require a black level that is over 10 million times dimmer to be unable to see it.
I think these are important topics to discuss as many are unaware and use this as a deciding factor when making a decision.
Perhaps, but your broach the subject in such a way as to make meaningful discussion almost impossible, ie claims that are easily disprovable like, the above, or your 100:1 maximum comment.
Question for you? Why would companies and industries that supply mission critical solutions such as Barco, DPI, Christie etc. only use Ansi contrast?
Because it is the only measurement for contrast that has actual standards and real world value.
It may be the because it is the only one with a standard. That said let me throw this back at you:
Version 1.2 of the DCI Digital Cinema System Spec states the following:
The sequential contrast ratio is computed by dividing the white luminance (of a peak white field) by the black luminance (of a black field). The nominal (reference) value is required to have a minimum sequential contrast of 2000:1. The tolerances for mastering and exhibition are shown in Table 11: Reference Image Parameters and Tolerances. In order to eliminate unwanted detail or discoloration in near blacks, it is critical that Mastering Projectors have an equal or higher sequential contrast than all exhibition projectors.
Note that this is a measurement of the sequential contrast of the system. It includes the projector and the ambient light on the screen.
If ANSI contrast is the only thing that has "real world value" why did DCI write into the specification for digital cinema a requirement for a minimum sequential contrast?
The answer is because it matters. It should also be noted that there is no requirement in the DCI Digital Cinema System Spec for an ANSI contrast value.
Originally Posted by trans_lux
Further how is using a full white image ON then a completely black image OFF in a black box pointing into the lens at an unknown distance with absolutely no ambient light present representative of real world use?
Because it measures the two extremes which the device must be able to reproduce. It must be able to reproduce peak white (measured by the white image) and complete black (measured by the black image). Real world content makes use of both. If black level is high, space looks milky/gray instead of black, if white is low, snow capped peaks look dim and dingy. Since contrast is white/black, a high contrast ratio is important. It should also be noted again, that very, very few scenes have 50% average luminance, which is what ANSI measures. Most scenes where black really matters are closer to (or lower than) 1%.
Also you didn't answer my question re: why ansi contrast is used as the only standard for professional displays and industries.
It's not, DCI requires Sequential Contrast measurements, but NOT