light and colour

[deranged-angel]

Hello all,

just wondered if someone could tell me if I have got this right.

Ok

 

Additive mixing is when you have (for example) three lanterns, with different gels on and you add the colours to the stage.

The colour wheel is red, blue and green on outside as primaries, yellow, cyan and magenta as secondaries and white in the middle cos that's what you get when you have the full spectrum.

 

Subtractive mixing is when you put more than one gel on the same lantern. Is the colour wheel different for this? Some books I have don't say so but some internet sites say there is black in the middle and that the colours mix like paint does, i.e. red and blue makes purple. Surely this cant be right? If it is then I am very baffled indeed.

 

I dont trust the net as much as I trust the books but the books dont mention a second colour wheel....

 

Emma

xxx

(confused and dazed) :huh:

[P. Funk]

additive colour mixing you got right.

 

subtractive colour mixing, is when you are taking away light from white, rather than mixing colours together on stage. it uses cyan, magenta, and yellow.

 

cyan 'subtracts' red from the source

magenta 'subtracts' green from the source

yellow 'subtracts' blue from the source.

 

thus, if you put a cyan and a magenta filter in front of a light source, you get blue light out the end, as the red and green have been filtered out.

 

if you put all three colours in front of a white source, you get absolutely nothing out.

 

you can either use additive or subtractive mixing. an example of additive mixing is in a thomas pixelpar, or NJD spectre. you dim the red, green, or blue channels, and when they are all up, the RGB light mixes and you get white. so you use 3 different light sources, and no colour filter.

 

subtractive mixing is used in most automated wash fixtures. it is used when you have one constant white light source - CMY filters get in the way of the beam and filter it into the colour you want.

[deranged-angel]

Ahhh ic.

So, if I put a yellow filter and a blue-green filter over the same lantern, I will get a green colour because yellow is a part of green?

 

Good job I asked cos I'd have looked like a bit of a pratt telling my class the wrong thing :huh: (class presentaion)

 

Thanks very muchos!

 

Emma

xxx

[P. Funk]

yeah that's exactly right. good luck with your presentation

[deranged-angel]

:)!

 

thanks!!!!

 

 

Emma

xxx

[Brian]

Nice explanation P.Funk.

 

Just a couple of things to add.

 

1/. Subtractive mixing is also what happens in printing, you print with Cyan, Yellow and Magenta inks. As with filters they absorb the light falling on them and allow the remaining colour to reflect. Print all three and you get black - well not quite you get a horrible muddy brown, which is why colour printing also introduces a 4th ink - black.

 

There are other colour printing processes using more inks to achieve certain effects.

 

2/. Ignore the whole paint thing. Paint mixing only works because the pigments in the paint aren't pure colours. If you try to apply the subtractive mixing principle to paint you will get very confused. Take your example...

like paint does, i.e. red and blue makes purple

which is what we were all taught. But the red paint should absorb everthing but the red light and the blue paint should absorb everything but the blue light. Since they are mixed together it should mean that all light is absorbed!!!

[Potassium Neuf]

True - a lot of people get the paint and light thing confused, probably because some combinations appear to work the same and others don't:

 

For example, in light -

 

Blue and Green gives you Cyan (Turquoise, bluey-green) :D

 

Blue and Red gives you Magenta (bluey-red) :huh:

 

Red and Green gives you Yellow (honest really - it does) :huh:

[Brian]

I have wonderful 'discussions' with my wife who is an art teacher about colour mixing theory. :huh:

[deranged-angel]

So if I put a cyan, magenta and a yellow gel on the same lantern I would get 'black' light so to speak? no, that's not right cos they are part of the full spectrum so they would give me 'white' light? argh!

 

One of the books I have says that if you put a gel on a lantern at a low level intensity, you get a muddy colour. I understand this is because the low colour temperature gives off a yellow colour so you are effectively using subtractive colour mixing but why does it come out dark???????!!!!!

 

Am I being really stupid now?

 

em

xxx

[Brian]

So if I put a cyan, magenta and a yellow gel on the same lantern I would get 'black' light so to speak? no, that's not right cos they are part of the full spectrum so they would give me 'white' light? argh!

Think of it in 3 seperate steps..

 

Step 1 - White light through Cyan Gel - Red absorbed, Green and Blue passed

 

Step 2 - Green and Blue light through Magenta Gel - Green absorbed, Blue passed

 

Step 3 - Blue light through Yellow Gel - Blue absorbed, nothing left to pass.

[Tom]

In very simple terms:

 

White light contains all the colours of the spectrum - that is Red, Blue and Green.

 

By putting gel in front of a light you are subtracting colour from the spectrum. Red gel subtracts Blue and Green light to leave just the Red. If you then put a piece of Green (or Blue) gel in front of the same light, it would subtract the Red and you would be left with nothing. (This assumes you are using true colours - you'd probably actually still get a bit of transmission).

 

Now, if you shine a red light at a white wall it will go Red. Shine another light, this time Blue at the same wall and the wall will look Magenta - you've added Red and Blue light together. Now add a third light in Green and the wall will look white again because you have added the three colours together to make white.

[deranged-angel]

ahh yes.

 

I knew that!! Just getting jumbled up for a minute there!! :huh:

 

Thanks

 

em

xxx

[Just Some Bloke]

The trouble with the theories above is that they all require you start with perfect white light. If you take a tungsten halogen lamp (not true white to begin with) and then burn it at a low level, what's coming out is nothing like white. So now the theories don't work any more. This is why:

 

QUOTE:

"One of the books I have says that if you put a gel on a lantern at a low level intensity, you get a muddy colour"

 

If you take a colour that doesn't have much blue in it to begin with and then take away more blue, for instance, it doesn't take much till there's no blue left at all. And if you take the same starting colour which already has a lot of yellow in it and then add a green gel, you'll get 'a muddy colour'.

 

Two choices here: in theory you should put colour correction gel in first (e.g. 202) then the colour of your choice - not recommended because you won't get much output as you've taken away too much light - or you simply choose your gel bearing in mind not to go too yellowy and to add more blue than you otherwise might.

 

Then of course it's all different again with Parcans becasue their colour temperature is different again. It's a nightmare!

[TomLyall]

as useful as the theory is... and dont get me wrong I dont have anything against it, in find the easiest think to do is to carry a gel sample book with you (avaliable from most places) and just test them infront of the desired lantern...

[deranged-angel]

in light (no pun intented) of the last posts, my presentation on subtractive mixing is going to go as follows:

 

In a theatre, carry round a gel sample book, give yourself enough time to try out colours using the afore mentioned sample book and order in the colour you want.

 

ta-da!!!!

 

Think I'll pass?!

 

Aside from that though, it is quite useful to give a bit of advice from the professionals in that you guys don't really recommend subtractive mixing as a reliable way of mixing colour.

 

 

Emma

xxx