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Hi,

 

Was watching TV on my project and a question struck me.

 

My projector is in the living room and there is warm lighting. The screen does not look black at all when the projector is not turned on. However, when the projector is turned on, the "black" (e.g. human hair) look darker than the screen. How can this be possible? Is it the case where the contrast play a trick on the eye?

 

 

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Hi,

 

Was watching TV on my project and a question struck me.

 

My projector is in the living room and there is warm lighting. The screen does not look black at all when the projector is not turned on. However, when the projector is turned on, the "black" (e.g. human hair) look darker than the screen. How can this be possible? Is it the case where the contrast play a trick on the eye?

 

 

 

It's just an illusion. For projectors, no light on the screen = "black". Which is why they work best in dark rooms.

 

Regards

CK

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Black is a colour and it's not the same as the absence of Light ( Dark or dark scene ). .Therefore,  a well calibrated projection will be able to see Black on dark scene / Raster better.  When the projector is off,  the screen reflects ambient light, so we see it white or maybe yellowish when halogen light is being reflected,

The human brain perceives the image in the same way as we use a Black marker to write on a white paper.

Raster - is referring to "no signal state" where the projector will cut a very very light  "lighted box".

 

So, here is another question i.e. if the screen is black,  can we still see the BLACK colour ? ::)

 

Here goes the answer:-

 

Even though we use a Black Screen, the colour black can still be observed.

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I cannot understand your explanation .... :-[

 

But I do understand that the screen has to be reflective in nature. If it is black (e.g. due to the absorption of all visible light) than it will look black even when the projector is on.

 

In my case the screen is slighly yellowish (due to warm lighting) to start with. I don't see how can a projector makes it look "darker" by shinning some light on it. But I can accept that this is all mind preception..

 

I encourage everyone here to do a test. Switch on some ambient light and watch a movie. Do you think the human hair look darker than the part of the screen that is out of the projection area?

 

Black is a colour and is not the same as absent of Light ( Dark or dark scene ) .therefore a well calibated projection will able to see Black on dark scene / Raster better .when the projector is off the screen reflect ambient light so we see it white or maybe yellowish when halogen light being reflected,

the human brain percesive the image in the same way as we use a Black marker write on a white paper.

 

So , here is another question if the screen is black can we still see the BLACK colour ? ::)

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I cannot understand your explanation .... :-[

 

But I do understand that the screen has to be reflective in nature. If it is black (e.g. due to the absorption of all visible light) than it will look black even when the projector is on.

 

In my case the screen is slighly yellowish (due to warm lighting) to start with. I don't see how can a projector makes it look "darker" by shinning some light on it. But I can accept that this is all mind preception..

 

I encourage everyone here to do a test. Switch on some ambient light and watch a movie. Do you think the human hair look darker than the part of the screen that is out of the projection area?

 

 

Correct. Unlike drawing with a black marker on a white surface, a projector throws light onto the screen. There is no way you can throw "black light", so black is simply the absence of light. Same for LCD (black = the pixels block the backlight), Plasma/CRT (the pixel is off). Same theory for watercolour paintings - there is no "white". White is from the paper.

 

That's why companies like Stewart has got grey projection screens. By darkening the screen slightly, you get a better "black" without compromising the white too much.

 

Regards

CK

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Wait till you see a BLACK screen > ( SONY have demonstrated that )

there is also the Nova diamond Black screen .

It's as simple as I have said,  BLACK is a color not absence of light , try it if you have a projector/ Take a black paper and paste it on your screen and I can tell you, you will still see BLACK if you go close enough.

Even without signal the projector will still have light projected onto the screen, if Black is the absence of light, then is that to say, projector can't produce black if there is still Light ?

can't compare to direct view display as the faceplate is dark in the first place.

Go to Changi Airport, you can see the image projected on a see thru screen ( hologram ) you can see the BLACK on the see thru screen .

 

I think anyone who have a dila projector can tell what is dark from BLACK.if you have not seen it, then you need a calibration disk and check it out yourself.

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Correct. Unlike drawing with a black marker on a white surface, a projector throws light onto the screen. There is no way you can throw "black light", so black is simply the absence of light. Same for LCD (black = the pixels block the backlight), Plasma/CRT (the pixel is off). Same theory for watercolour paintings - there is no "white". White is from the paper.

 

That's why companies like Stewart has got grey projection screens. By darkening the screen slightly, you get a better "black" without compromising the white too much.

 

Regards

CK

 

If Black is the absence of light, then how you can get a darker BLACK as there is no light - which you can't even see ? ???

 

Just like how to get a number, if everything is multiplied by Zero ?

1x0 = 0

2x0 = 0

anything x 0 is still Zero? , then how a Gray colour can get a darker Black if there is no light ? As we know, it does get a darker black and can we say it reflects less light so the black looks deeper ? if yes, then BLACK is what ? still the absence of light ?

Alf , where are you ? Please help...

 

Peng

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It's very simple. If BLACK is the absence of light, then there is NO white when there is Light? Are we say White is not a Color

 

Maybe, we should put it "Black is all light being absorbed and non-reflected back" then "White is light being fully reflected from the colour spectrum".

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Black = no light on a white surface.

 

Ideally, the screen must be in a room with no light and everything will appears as "black" only where area of the picture pixel need to be "brighter than black" then, as in the case of a LCD projector, the LCD panel will unblock that pixel to allow light from the projection lamp to lit up that spot.

 

Light from any other source would be unacceptable as this will bring up the "black level" of the picture.

 

(Audio)

 

 

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Black = no light on a white surface.

 

Ideally, the screen must be in a room with no light and everything will appears as "black" only where area of the picture pixel need to be "brighter than black" then, as in the case of a LCD projector, the LCD panel will unblock that pixel to allow light from the projection lamp to lit up that spot.

 

Light from any other source would be unacceptable as this will bring up the "black level" of the picture.

 

(Audio)

 

 

 

+1, mate is my short contribution.

 

 

 

The longer version is as follows:

 

I think this discussion depends on the situation. Mustn't get confused over semantics and situations.

 

Pigment colours and light colours are also different.

 

Using high school physics, there are no colours! We perceive colour through the wavelengths of light that are reflected back from an object which are not absorbed. Light and colour are all just wavelengths.

 

For example chlorophyll absorbs red and blue light, the remaining light wavelength that is reflected back is green. Hence why chlorophyll looks green. White light is all the colours, basically your white screen doesn't absorb any colour and reflects all colours therefore it appears white.

'Black' objects absorb all light therefore they appear black- the 'absence of light'. Put any object of any colour in a room without light and we will perceive it to be black. Thats why a black hole is black it absorbs any light and can represent the absence of light.

 

Add light and then it depends on the wavelength of the light used. Hence a 'pink' light can make a 'white' screen appear pink.

 

 

I don't know much about LCD projectors but my grasp of it is that they cannot display blacks v well as they still need to shine light through the LCDs and the spill over light dilutes the blacks that would otherwise be possible.

 

Of course this is not my day job, so anyone who knows more please feel free to contribute/ correct me.

 

J

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The way how our eyes perceives contrast and colours is the very fundamental factor that we've overlooked.

 

Our eyes have got a built-in "dynamic aperture". Furthermore, at different ambient brightness, our colour perception varies. The static contrast ratio of our eyes is much smaller

 

So, in ambient warm light, our white screens appear yellowish. Fire up the projector, and the heightened brightness reflected off the screen alters our colour perception and contrast differentiation.

 

All projectors will leak a finite amount of light when it is supposed to display black. But because our eyes are so easily tricked, even a black screen can be made to appear white under the right conditions.

 

So, how does a projector display black? It doesn't. It just makes the white looks incredibly brighter.

 

 

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If Black is abent of light , than how you can get a darker BLACK , as no light you can't even see ? ???

 

Just like how to get a number , if multiple by Zero ?

1x0 = 0

2x0 = 0

anything x 0 is still Zero ? , than how a Gray can get darker Black if there is no light ? as we know it does get a darker black and can we say it reflect less light so the black look deeper ? if yes than BLACK is what ? still absent of light ?

Alf , where are you ? Please help...

 

Peng

 

I think Jag got it.

 

So, how does a projector display black? It doesn't. It just makes the white looks incredibly brighter.

 

Technically you can't project "black". Technology does not exist yet for this to happen. The grey screen simply gives you a darker "black" than a white screen, while not sacrificing the whites too much.

 

While your projector is projecting a "black" scene, pause the source, and block off part of the light with your hand or some other object, you'll see that it's roughly the same. Block off the entire light beam from the projector, and the screen returns to the off-white/yellow/whatever ambient light you have.

 

We all know that LCDs are inferior to plasma, their "black" is actually very dark grey. But do we see it? No, we still perceive it as "black". It's all an illusion.

 

Yes, a darker scene (including "black") reflects less light. Black is the absence of light. When you look up to a clear sky at night at a place without light pollution, all is black as there is no light. True black (RGB: 0, 0, 0) probably does not exist in display technologies yet.

 

Regards

CK

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To quote from your source:

Isn't this the absence of light?

 

Regards

CK

As the above said "No visible light", it means you can't see it and it does not mean they are not there.

Eg. infared / ultraviolet - you can't see them but they are there.

Read deep into it.

Black light is be projected/emitted/radiate

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The way how our eyes perceives contrast and colours is the very fundamental factor that we've overlooked.

 

Our eyes have got a built-in "dynamic aperture". Furthermore, at different ambient brightness, our colour perception varies. The static contrast ratio of our eyes is much smaller

 

So, in ambient warm light, our white screens appear yellowish. Fire up the projector, and the heightened brightness reflected off the screen alters our colour perception and contrast differentiation.

 

All projectors will leak a finite amount of light when it is supposed to display black. But because our eyes are so easily tricked, even a black screen can be made to appear white under the right conditions.

 

So, how does a projector display black? It doesn't. It just makes the white looks incredibly brighter.

 

 

 

Jag ah,

The black we see from a projected image is made of. How we see it from dila, lcd or even DLp. It's  not really black or light being blocked but something we selected from the optical wavelength (blue spectrum ) and How we use the S phase and P phase light and that is also the reason  why even panny and eson use the same LCD panel but the colour of Black look different . Go SID site and dig deeper.

Btw , you have a chance 2c the SONY demo on their Black screen ? you still out there or back ?

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As it say No visible , means you can't see it and does't means they are not there.

infared / uatrvoiet you can't see them but they are there.

Read deep into it.

Black light is be projected/emitte/ reflect

 

I beg to differ.

 

When a projector projects "White", most of the light from the bulb goes to the screen, which reflects most of it to you.  When it projects red, independent of projector technology, red light eventually hits the screen, which reflects the red back to you.

 

Any combination of R, G and B in the projector will produce the vast numbers of colours you see, except black. For example, full red will be RGB(255, 0, 0), Yellow will be RGB(255, 255, 0) and so on. And full white is RGB(255, 255, 255).

 

Black is represented digitally as RGB(0, 0, 0). The LCD in a LCD projector will now block the light (most of it anyway) so that it doesn't reach the screen. In reality, some light still leak through, showing up as a very dark grey instead of black. Let's leave the other technologies like DLP out for now, as they are more complicated, but the end results are the same. The desired mix of RGB arrives at the screen and is reflected back to you. In fact, the "black" from the projector is lighter than the white of the screen because of the light leakage, but you'll perceive it as black anyway.

 

The reason why the "black" you see when the projector is receiving no signal, vs when it's displaying a person with black hair is all an illusion, just like the one posted earlier. It's how our eyes perceive colour.

 

Light is additive, you cannot produce black using light. It's simply produced by not having any. You can't see IR/UV, so it doesn't matter that they are/aren't there. What matters is that very little light reaches your eyes, and your brain perceive it as "black".

 

Regards

CK

 

 

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http://en.wikipedia.org/wiki/Ultraviolet

maybe this will make it easy why we see a darker /solid black on image projected from Dila. Some of us in the projection field call it fluorescent BLACK.

 

I fully understand what Jag have said and he had answered well in layman terms for the this thread initiator.

I also accept the explaination from Jimi - based on whether the discussion is based on the academic or scientific/imaging field.

 

But in projection, the black or no signal status is not projected in the RGB Color Mode as 0.0.0, however,

there is no point for me to go further in details on how the optical engine works and how the S-phase light

and P-phase light being converted to produce a "so-called" inky-black -  too engineering.

 

Peng

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http://en.wikipedia.org/wiki/Ultraviolet

maybe this will make it easy why we see a darker /solid black on image projected from Dila. Some of us in the projection field call it fluorescent BLACK.

 

I fully understand what Jag have said and he had answered well in layman terms for the this thread initiator.

I also accept the explaination from Jimi - based on whether the discussion is based on the academic or scientific/imaging field.

 

But in projection, the black or no signal status is not projected in the RGB Color Mode as 0.0.0, however,

there is no point for me to go further in details on how the optical engine works and how the S-phase light

and P-phase light being converted to produce a "so-called" inky-black -  too engineering.

 

Peng

try us, i'm intrigued to know more about this ability of projectors to project black.  i've tried looking up "fluorescent black", "s-phase" and "p-phase", and without investing too much time and effort, am unable to come up with any answers.
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try us, i'm intrigued to know more about this ability of projectors to project black.  i've tried looking up "fluorescent black", "s-phase" and "p-phase", and without investing too much time and effort, am unable to come up with any answers.

 

I still don't think it's technically possible. If it were, then we can just use this technology to shine at something and it'll become black. At night, it's great for making things disappear.

 

Regards

CK

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I don't know why is it so difficult to just use simple common sense; black = no light on white screen.  The projector, in any ideal case, does nothing to any black portion of the picture, it only use to light up anything above black (no light).

 

If you want to "project" black as in "remove ambient light from the screen" to make it "more black" then you don't need a projector....you just need a black hole to suck the light out of the screen, it is as simple as that.

 

(Audio)

 

See what "Star Trek" did to me....   :)

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I don't know why is it so difficult to just use simple common sense; black = no light on white screen.  The projector, in any ideal case, does nothing to any black portion of the picture, it only use to light up anything above black (no light).

 

If you want to "project" black as in "remove ambient light from the screen" to make it "more black" then you don't need a projector....you just need a black hole to suck the light out of the screen, it is as simple as that.

 

(Audio)

 

See what "Star Trek" did to me....   :)

 

Totally agree with you, and that's the point I've been trying to put across.

 

This question has also been asked all over the place, the answer is the same. Black = no light.

 

http://www.google.com/search?q=how+does+a+projector+project+black+light%3F&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a

 

Regards

CK

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The way how our eyes perceives contrast and colours is the very fundamental factor that we've overlooked.

 

Our eyes have got a built-in "dynamic aperture". Furthermore, at different ambient brightness, our colour perception varies. The static contrast ratio of our eyes is much smaller

 

So, in ambient warm light, our white screens appear yellowish. Fire up the projector, and the heightened brightness reflected off the screen alters our colour perception and contrast differentiation.

 

All projectors will leak a finite amount of light when it is supposed to display black. But because our eyes are so easily tricked, even a black screen can be made to appear white under the right conditions.

 

So, how does a projector display black? It doesn't. It just makes the white looks incredibly brighter.

 

 

You make an excellent point. Contrast is perceived as a relative factor. The visual system is vastly more complex than just a dynamic iris- but your point is still valid.

 

Our eyes detect contrast as a major part of our vision. Raising the 'white' in a scene will make the blacks appear darker up to a point. After that point, the blacks will start to appear lighter as the retinal pigment epithelium bleaches out due to too much light entering the eye. Way before that happens, turning off the ambient light will help increase the contrast ratio further to make the blacks blacker.

 

 

http://en.wikipedia.org/wiki/Ultraviolet

maybe this will make it easy why we see a darker /solid black on image projected from Dila. Some of us in the projection field call it fluorescent BLACK.

 

I fully understand what Jag have said and he had answered well in layman terms for the this thread initiator.

I also accept the explaination from Jimi - based on whether the discussion is based on the academic or scientific/imaging field.

 

But in projection, the black or no signal status is not projected in the RGB Color Mode as 0.0.0, however,

there is no point for me to go further in details on how the optical engine works and how the S-phase light

and P-phase light being converted to produce a "so-called" inky-black -  too engineering.

 

Peng

 

UV light in the form of a Wood's light or Black light is just a UV bulb. Commonly used in medicine for dermatologists, and similar to the black bulbs in night clubs. Doesn't produce much light though and of course it can't produce a black light.

 

Re: the s and p phase light:

You don't need to go into how its done. But a simple explanation of the principle would be interesting.

Assuming light is a wavelength, do they produce light out of phase to help cancel out some of the light leakage?

 

I thought LCD and DLP have different blacks based upon how they produce light- with the DLP method being more efficient with regard to light leakage?

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There is no such thing as black light. Black light as a term is a wrongly coined word to describe Ultra-violet portion of the visible light spectrum. This error has been around since the late 1800's.... but its the common word to describe UV light today. UV is very low down in the blue portion of the optical spectrum... purple-ish (i.e. violet). Because we cannot see UV light, we only see the potion of UV that spills over into the visible spectrum of light (i.e. blue-ish)

 

In all history of display technologies, black is always been represented by a minimisation of photonic energy,.... i.e. CRT TV, CRT projectors, DLP, LCD, DILA. Unless someone can show proof with citation from a SID paper that black can be projected, then its still the laws of physics that stands....no light = black.

 

If black can be projected, I'd dare say that's the ultimate in stealth technology.

 

 

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