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Thread: Light and colours. I'm confused.

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    Light and colours. I'm confused.

    Ok, I know this is not really a photography thing, but as light is used, I may get some help anyway.


    Here goes:
    In this day and age, we seem to resolve things down to 3 colours. Red, Green and Blue.
    Though when I was at school I am sure Yellow was in there somewhere and Green wasn't, well in painting anyway.

    So with "RGB" and electronics we can make an colour we want which is why televisions use those three colours.

    These are called PRIMARY colours - dur.

    There is a thing called a photo-spectrometer (spelling) which basically has a prism and you get a "colour map" (or what ever it is really called) with black lines indicating a unique colour signature for that specific colour. Yeah, ok, badly explained, but it is only 07:20 and I am trying to get this sent off before I start work.

    Maybe for simpicity's sake they say the colour is broken down into THREE colours, which is why I am confused - because:


    Recently I learnt that the rainbow has SEVEN colours. That is a bit more than three.


    Is this why there are some expensive printers which have seven colours as opposed to the typical 4 (CMYK)?

    I understand a bit how RGB and CMY are related. One is for electronic referene and one is for printing. R+G+B = white. C+M+Y = black.

    I've forgotten the pairing of the colours, how R = C+M (for example) or C-M.... What ever.



    Could someone help me understand a bit more about what is going on with the actual colours, how many are "claimed" to exist/are needed and that kind of stuff.

    Yeah, sorry for the vagueness, but I don't quite undertand the bigger picture myself, so it is difficult to ask the question in a sensible way.
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    Administrator ricktas's Avatar
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    RGB is just a system that allows SOME of the colours that exist to be displayed and printed. It is a simplification!

    Your camera and screen cannot produce all the colours the human eye can see, it can display a limited (but well chosen) range of all colours.

    A rainbow really has 9 colours, cause it also included infra red and ultra violet at each end, as well, but these are outside the spectrum visible to humans.

    Colourspace theory is a huge field, as is colour in general. What our cameras, screens and printers do, is produce a result that contains a good range of colours, that, to the human eye appear to represent what we see, with a reasonable amount of accuracy. If you want to start studying colour theory, be prepared to put in a LOT of time.

    Colour Theory

    Colourspaces (as used in camera's, printers, screens and more)

    and to add even more, there is the difference between reflected light (on a print) to transmitted light (on a computer screen). To get black on a print, the inks Red Green and Blue are each used in equal amounts to produce black, and we see the light reflected off the surface of the print as black. Light from a computer screen is transmitted (the light comes out of the screen), and to get black you have NO RGB mix, in fact the pixel is turned off (no colours at all). Red Green and Blue are mixed together in equal amounts, to produce white on a tv, monitor, screen!

    Think of it this way. most prints are printed on white paper, thus colour has to be added to produce black. On a screen, when it is turned off, it is black, thus adding colour is needed to make white.

    See, told you colour theory was a big field.
    Last edited by ricktas; 06-01-2012 at 8:18am.
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    I am older than I look. peterb666's Avatar
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    Rick, that last bit is on the right track but a bit misleading. Printers mix cyan, magenta and yellow to produce black. As the mixing is rarely spot on, the black may appear as dark grey or have a colour cast and you normally also have a black cartridge as well. This is known as subtractive colour. Take away fhe colours and you have white. That's why you print on white paper.

    Monitors use addative colour. Add together red, blue and green to get white.

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    Administrator ricktas's Avatar
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    To add,

    You ask how many colours, well three, in RGB, but used in different mixes they can produce a range of vibrant and brightness levels to produce a huge range.

    The human eye can perceive : 2.2 - 2.3 million colours
    sRGB is capable of producing 909,800 colours
    Adobe RGB is capable of producing 1,320,550 colours
    Last edited by ricktas; 06-01-2012 at 8:32am.

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    Administrator ricktas's Avatar
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    Quote Originally Posted by peterb666 View Post
    Rick, that last bit is on the right track but a bit misleading. Printers mix cyan, magenta and yellow to produce black. As the mixing is rarely spot on, the black may appear as dark grey or have a colour cast and you normally also have a black cartridge as well. This is known as subtractive colour. Take away fhe colours and you have white. That's why you print on white paper.

    Monitors use addative colour. Add together red, blue and green to get white.

    Sent from my GT-I9100 using Tapatalk
    True, but also paper that is white is not necessarily 'white' either, which will affect the end result too.

    I was, hopefully, just trying to point out the basic science behind it. If someone wants to study colour theory and colourspaces, I think they need to look at some of the vast resources on it, on the net. A thread on AP is not going to cover it all.

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    Thanks for the replies.

    I understand that printing is subtractive - thanks for reminding me of the word Peter - where as RGB are addative.

    Ok, so along that track, why is it when I was at school - back in the dark ages - and we were painting - which I guess would be analagous to SUBRTRACTIVE - why were we using Red, Blue and Yellow paints?

    Ok, the terms Cyan, Magenta and Yellow weren't in the venacular, but I am sure the names existed.

    But Blue nearly equals Cyan - at a push.
    Yellow - well no comment.
    Red? Well I know there is that big thing about RED vs. SCARLET - which are different colours, but equating Red with Magenta?


    Hey, I'm just asking and thinking aloud a bit.

    I agree, here may not be the best, but to get an introduction to the concept, I would hope someone would be able to help me understand the differences of things then, and now and why certain colours were used then and different ones now.

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    Administrator ricktas's Avatar
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    As said above, you need to do a lot of reading on Colour theory, and Colourspaces to get your head around it. A thread on AP cannot give you all the information needed. It is almost a Science, in its own right. So start googling, or click the links in my post above, and spend a day or three, reading.

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    Ok, thanks.

    Shall do.

    Just wanted to check.

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    Arch-Σigmoid Ausphotography Regular ameerat42's Avatar
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    And also research along the lines of "the perception of colour".
    CC, Image editing OK.

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    It's all about the Light!
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    As my user title says (Photography) It's about the light!
    So doing some basic study of colour and light is very helpful.

    Doing B&W images and concentrating on tonal range is the other part of it.
    Reading some of the classic texts by Ansel Adams (The Camera, The Negative, The Print) will help with the B&W understanding.
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    A royal pain in the bum! arthurking83's Avatar
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    So that you can quickly and easily visualise colourspace, look at a colour wheel.
    In the digital space, a colour wheel consists of 6 reference points.
    Those 6 points are split into two groups, RGB and CMY.

    RGB are equally spaced over a 360° period(ie. at 120° apart from each other) and the CMY are also spaced 120° apart from each other, but you will see why they all correlate to each other if you look at the colour wheel.
    The RGB points are offset by 60° to the CMY reference point, so that C is half way between G and B, M is half way between B and R, and Y(yep .. the old classroom fave... Yellow!) is half way between R and G.

    Once you appreciate this, you'll then see why some image editing software have colour balance adjuster tools that adjust colours along certain axes.
    eg, if you adjust for warmth, you adjust along the B-Y(blue-yellow) axis, because blue and yellow are at the opposite points of the compass.
    .. if you adjust for tint for a whitebalance tweak, you're adjusting the M-G(magenta-green) axis.

    etc, etc.

    As for printers, a very high end printer may have up to 11 individual ink types, which includes various incarnations of black(gloss, matte) etc, and some have gloss finishers to even out gloss finish of various colours.

    A good printer will have 7 inks, and better printer will have 9 ... the difference is in how subtle variations in colour grades are rendered or printed.

    Note tho, as in part of your original question, the printer still has yellow as a primary colour.
    The difference in why it uses C for blue and M for Red, is in the way they print.
    It's a system called halftoning, or screening.
    That is, these 'half colours' being halfway between the RGB primaries, blend together more accurately to produce other tones of colours.
    So if the printer use RBY instead, it would be harder to blend the more saturated colours to produce half tones .. a white additive colour would then also be required to produce many different shades of these tone, where the C/M colour tones blend more easily to produce those same tones.

    in effect, the use of CM with Y in printers is there for more accuracy in toning.
    Those 7, 9 11 or more colour tank printers, simply have even more accuracy that a simple 4 colour CMYK printer.
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    It isn't I am trying to be difficult, but again:

    I am thinking aloud and would like help understanding what I am reading - in basic form anyway.


    Ok, it has been shown there are different ways of defining light and how we see things, and how colours are made up.

    Now it is said there are SEVEN colours in the rainbow. But I guess now what is interesting me is how these are defined.

    Given they are colours like: Red, Orange, Yellow, Green, Blue Violet, Magenta - or what ever.
    Our eyes have only 3 (or 4) colour receptors. Red, Green, Blue - and some say Scarlet also.

    Keeping it simple, I'll say there are three different colours detected by our eyes: RGB.

    So how is it that it can be said there are SEVEN primary (bad choice of word?) colours of the rainbow if we can only detect 3 PRIMARY (again: bad choice of word?) colours?

    Maybe that is what I am sticking on.



    (Edit)

    Ok, reading that there are a limited combination of RGB mixes to give a finite GAMUT of colours (persoally I'd call it a pallett, but.....)

    So ok, we can see "X million colours" and there are even more than that - excluding Infra-red and Ultra-violet - but doesn't it come down to perception/relativity?

    If we can only see this X million colours and though there may be/are more, as they are beyond our perception with our eyes, don't they then become a bit accademic?

    I understand that the extra colours do go into making a better "tappestery" of colours (GAMUT/Pallett), but I'm still stuck in how they all fit together if we can't see them.


    Thanks.
    Last edited by Mr Felix; 06-01-2012 at 11:35am. Reason: a bit of clarification

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    Arch-Σigmoid Ausphotography Regular ameerat42's Avatar
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    Quote Originally Posted by Mr Felix View Post
    Now it is said there are SEVEN colours in the rainbow. But I guess now what is interesting me is how these are defined.

    Given they are colours like: Red, Orange, Yellow, Green, Blue Violet, Magenta - or what ever.
    Our eyes have only 3 (or 4) colour receptors. Red, Green, Blue - and some say Scarlet also.

    Keeping it simple, I'll say there are three different colours detected by our eyes: RGB.

    So how is it that it can be said there are SEVEN primary (bad choice of word?) colours of the rainbow if we can only detect 3 PRIMARY (again: bad choice of word?) colours?
    Eyes see and brain interprets, yielding 7 or 70 or 700 or... different hues. Ie, perception. Bees might "see" the rainbow in a completely different way, not to mention walruses. You are right to be confused: it's a difficult topic and broad as it is deep. Paddling about the edges is about as good as it gets 4 me anyway.
    Last edited by ameerat42; 06-01-2012 at 11:39am.

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    Administrator ricktas's Avatar
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    Cause from those 7 primary colours you can make up all the colours we can see with human eyes (over 2million of them). So they are called the Primary colours cause they are the basis of every single one of those 2 million other shades, tones, brightness, and saturations of those original 7 main colours.

    Using RGB we can replicate about 1 million of them. Using CMYK we can get to about 1.4million. Still over 600,000 colours missing, to get to the full gamut that the human eye can detect. So only using all 7 can we get close to that. BUT at present the technology is still not advanced enough to quite get us there, with the full human scope of colour being able to be represented in a print.
    Last edited by ricktas; 06-01-2012 at 11:38am.

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