How do you display black with a projector?

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ExigeEvan

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So, I was watching Man Utd v Chelsea in the Student Union today and in my boredom (can't say I find an entire football game that fun, but it beat revision) it occured to me that the projection screen was white and yet the projector was able to show black.

Now from my understanding black comes about from the absence of reflected visible light. So how can you project black?

Or did I just fall asleep in my physics A level lectures?
 
It gets "black" by mixing all the colours together, but it's not really black, it's just a very, very, very dark grey, a bit like socks.

That's right, Dougal. You see, ordinary shops sell what look like black socks, but if you look closely, you'll see that they're very, very, very, very, very, very, very dark blue.
 
I thought if the lights were off and the projector just doesn't project on that spot, no light is hitting it and therefore light doesn't reflect back into your eyes and it looks black.
 
Unless it's emitting it's own light, even something white will be black in the dark. Assuming the lights are off, a projection screen will look black, except for the parts where light is shining on it.
 
It gets "black" by mixing all the colours together, but it's not really black, it's just a very, very, very dark grey, a bit like socks.

Projectors are showing RGB, which is an additive colour set. All colours together make white. You are right in saying that it isn't a true black.
 
But the projection screen is white...

Not in the dark it's not ;) And even not in total darkness, your eyes will tell you it's black because of its relative darkness to the rest of the picture.

Stick your hand in front of the projector where the 'black' bits are and you'll notice it's just not projecting anything. Or a bit of red paper, and watch them turn red.

...unless you've managed to find some magical physics defying one.

Lemmy show you. For the school panto last month I (along with doing a whole bunch of other stuff) projected something onto the red curtains at the front of the stage for the start.

Here's what the projector displayed:

picture_1614.png



And here's what the file actually looked like:

picture_2625.png



See? The projector ignores the black bits, shows bright light for the white bits, and half light for the grey bits.
 
Yeah, the screen is reflective, not white, per se. If nothing's projected onto it, it reflects nothing, and in a dark room that's perceived as black. Even in a dim room, parts that are darker than elsewhere will be percieved as black.

Turn your TV or monitor off and look at the screen. It's not actually black, is it? Yet you see these letters as black.

As for how a projector displays black, it just doesn't project light into the black areas. Absence of light = black.
 
Unless of course you get one of those projectors where it has the ability to summon pixel sized black holes to suck up all light. They have a pretty high contrast ratio.
 
I do believe I was getting confused between projectors and printers. It's an easy mistake to make. Just don't ask me to print anything...
 
Okay, you guys seemed to be making sense. It's just a conin the end. It looks black cause everything else is lighter, pah.

I do believe I was getting confused between projectors and printers. It's an easy mistake to make. Just don't ask me to print anything...
Made me laugh cause the last James May column I read was about him fixing his 10yr old printer...
 
It gets "black" by mixing all the colours together, but it's not really black, it's just a very, very, very dark grey, a bit like socks.

:lol: great scene
 
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