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The Contrast-Brightness product (lessons from the Analog world)

963 Views 4 Replies 4 Participants Last post by  krasmuzik
As an analog guy, we usually talk about an amplifier's performance not in terms of gain (brightness in FP) or bandwidth (contrast in FP) but their product:

The gain-bandwidth product.

As a designer you're interested not in the "sheer" speed of the amp necessarily, but also how it behaves when you "gain" it up. That's why the gain-bandwidth product is so important.

The same happens in the FP world:

A high contrast ratio is great, but if it comes at the expense of brightness, then it loses a large portion of its applicability in the real world.

Consider the market leader at this point in time:

The RS1. Calibrated to D65 it makes about 600 lumens (correct me if I'm wrong) and about 15,000:1 CR at the SAME TIME.

Therefore, its Contrast-Brightness product is 600 * 15,000 = 9M lumens (contrast is a dimensionless number, we only have lumens left)

A future projector that is likely to dethrone this king will have to meet or exceed this number in order to be deemed a breakthrough product.

Let's just consider the IN82 that is coming to the market soon:

assume 1,200 D65 lumens.

In order to match the RS1's Contrast-Brightness product, its contrast ratio will have to be 7,500:1. If they can do it, GREAT!


Consider now another aspect of contrast that is considered by quite a few to be as, or even more, important than ON:OFF, the ANSI contrast.

If we add this new contrast into the equation, we have a new product of 3 variables:


On:Off contrast

ANSI contrast

Having formulated our new recipe, let's go ahead and plug in some numbers:

RS1: 600 lumens, 15k:1 On:Off, 250:1 ANSI = 2.25G lumens
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I don't really think that's as helpful, since there are two environments a projector is used. One is a batcave, where contrast ratio is very important, and lumens, less so. The other is a typical living room environment, where lumens is quite a bit more important than contrast ratio. Expressing performance as a product of the two loses all ability to gauge a projector's performance in your particular environment. Throw in other environmental differences such as the gain and size of the screen, and having seperate numbers for contrast and lumens to gauge performance becomes even more important. There is a point where more brightness doesn't really help in a batcave, and there is a point where more contrast doesn't really help in ambient light environments. Good idea when you don't consider the context... but it seems to me that we still need two numbers.
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Don't be giving marketing droids any ideas that all they need is a single massive number....

It is a good illustration of the tradeoffs - since dim PJ are usually hi contrast and brite PJ are usually lo contrast - and it does not make on any better than the other - though the high contrast high lumen PJ would be better than both while the lo contrast low lumen PJ is worst of all..

But I think this is better demonstrated in a contrast vs. brightness scatter plot so people can visually see which one has the better contrast*brightness while at the same time seeing which PJs are better for their environment so they don't buy brightness or contrast they will never use.
While more contrast with the same lumen is never a negative more lumen with the same contrast not necessarily since the black level goes up too. You are merely moving a window around. Your multiplication does not account for this.
One has to presume the screen gain & size are proper for the amount of lumens - then black levels will be identical when the contrast is the same. Just as it is a negative for a 300 lumen PJ on a 13' screen for poor white levels, so is a 1500 lumens PJ on a 6' screen with poor black levels
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