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why RGB and not RYB?

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i'm fealing really stupid now.. but in kindergarden I was tought that the primary colours were red, YELLOW and blue. Now I see that in graphics programming you get white by combining red GREEN and blue, and yellow is obtained by combining red and green?!?!?! why is that? can anyone explain?

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Red, green and blue are the primary colours of light ("additive" primaries). Each one emits more light, so you add up the total to get the final colour.
Red, yellow and blue are the primary colours of pigments ("subtractive" primaries). Each one absorbs more light, so you subtract to get the final colour.

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benryves is right. If you remember science class where they teach you the wavelengths of light: ROYGBIV (red, orange, yellow, green, blue, indigo, violet), then you'll see why.

A reason why computers often use RGB is because your computer display uses pixels which can only display combinations of red green and blue.

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There are two basic ways to get colors: additive and subtractive. The method typically used in art, graphic design, and other "analog" fields is based on RYB (or, more commonly, CMYK).

In CMYK, blending two colors subtracts them: base is pure white, and overlapping a pair of colors generally tends to make them darker. This is where you'll get black if you mush all the colors together. Subtractive models are close representations of what happens when you blend two pigments, such as paints or inks.

In computers, color is generated additively. Rather than mixing two pigments to color each pixel of the screen, monitors mix colors of light. The typical method is RGB. In this model, base is pure black (no light), and overlapping two colors generally tends to make them brighter, since you are combining two light streams.


Strict RYB also exists, but generally only informally in primary schools and the like; it is considered a poor physical model in the physics/optics realm and has far too many practical problems (like poor range) for use in printing.

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Quote:
Original post by swordfish
A reason why computers often use RGB is because your computer display uses pixels which can only display combinations of red green and blue.


Your causation is backwards [smile] Pixels are designed to emit red, green, and blue because those are the most effective additive primaries - the combination of them additively (i.e. by combining two light streams) yields the broadest and most efficient range of representable colors.

If gold, purple, and chartreuse were the most effective additive primaries, pixels would use those colors instead.

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well i dont know much about graphics theory but i think becuase rgb are the colors the pixels give out

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now it all makes sense
after some more reading on my own I can add that RGB is used for developing computer applications and CYMK for stuff that will eventually be printed

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Original post by firewall1
well i dont know much about graphics theory but i think becuase rgb are the colors the pixels give out


Like ApochPiQ has already said, pixels use RGB because its the best way of doing it, we don't use RGB just because the pixels use it.

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Of course we shouldn't forget on formats like.
RGB, RGB24, RGB30 (new emerging format that is unsupported on GFX cards yet), YUV, YUV2, YUV4, YRB, Y10R8B, YRB30, AYRB, ARGB, BGR, BGRA, ABGR, and I surely missed some formats used for computer screen.
Of course there also EBU standards, and ITU standards. Both of these has two variations, linear and that other one.

googling for "where is purple" might show a nice page with links and color diagrams.

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the RYB thing when used and applied in artist paints is actually as such:

There is no such thing as pure Red, pure Yellow or pure Blue when working with paints... I suppose it's theoretically possible to have it be a pure saturation, but that's never the case in practicality. Each one has a portion of a secondary colour.

Red can be either Red-Blue (purple) or Red-Yellow (orange)
Yellow can be either Yellow-Red (orange) or Yellow-Blue (green)
Blue can be either Blue-Red (purple) or Blue-Yellow (green)

As such, when using RYB in paint you actually need two of each primary in order to mix properly... You'll also want white and black because black is hard to mix and wastes a lot of expensive paint, it also never turns out due to pigment impurities especially in cheaper paints... And white because you just can't mix white from coloured pigments. They are each extreme hues which is actually the problem, paint mixing doesn't really take hue into account, you require the white and black to lighten or darken the colour.

As others have said, there is a difference in pigments and light blending when analyzed on a high level, but keep in mind pigments are simply the result of a substance which reflects and absorbs light. While mixing on a practical level is different, it's the same theory on a fundimental level... That is when you look at the actual light being bounced back into your retina.

Wikipedia knows

[Edited by - M2tM on September 19, 2006 8:53:20 AM]

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Quote:
Original post by Raghar
Of course we shouldn't forget on formats like.
RGB, RGB24, RGB30 (new emerging format that is unsupported on GFX cards yet), YUV, YUV2, YUV4, YRB, Y10R8B, YRB30, AYRB, ARGB, BGR, BGRA, ABGR, and I surely missed some formats used for computer screen.
Of course there also EBU standards, and ITU standards. Both of these has two variations, linear and that other one.

googling for "where is purple" might show a nice page with links and color diagrams.


Well, all the formats you said there are only formats of storing data in your memory. They are not displayed as they are, but converted to RGB first. Monitors don't know anything but RGB.

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Quote:
Original post by meeshoo
Quote:
Original post by Raghar
Of course we shouldn't forget on formats like.
RGB, RGB24, RGB30 (new emerging format that is unsupported on GFX cards yet), YUV, YUV2, YUV4, YRB, Y10R8B, YRB30, AYRB, ARGB, BGR, BGRA, ABGR, and I surely missed some formats used for computer screen.
Of course there also EBU standards, and ITU standards. Both of these has two variations, linear and that other one.

googling for "where is purple" might show a nice page with links and color diagrams.


Well, all the formats you said there are only formats of storing data in your memory. They are not displayed as they are, but converted to RGB first. Monitors don't know anything but RGB.


The same is true of print formats, but that doesn't mean that they don't have a purpose, I mean RGB is converted to whatever colours the printer has available afterall, you could argue RGB is just as arbitrary in certain circumstances... In fact, in the end you could say that all colour is irrelevant because it's your brain that does the processing in the end and it uses a network of neurons or whatever brains see colour as. That's a bit extreme, sort of a straw-man... But I'm not trying to destroy your point, just trying to contrast it.

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Cones in the human eye are attuned for short (blue), medium (green), and long (red) wave lengths of light. Although the long receptive cones actually respond more strongly too yellowish/green light. In anycase from a light mixing point of few (preface: I don't know much about optics) I'd imagine the distance between the wavelengths should be approximately equal for it to work well (hence why computer screens use red instead of yellowishgreen).

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Quote:
Original post by M2tM
Quote:
Original post by meeshoo
Quote:
Original post by Raghar
Of course we shouldn't forget on formats like.
RGB, RGB24, RGB30 (new emerging format that is unsupported on GFX cards yet), YUV, YUV2, YUV4, YRB, Y10R8B, YRB30, AYRB, ARGB, BGR, BGRA, ABGR, and I surely missed some formats used for computer screen.
Of course there also EBU standards, and ITU standards. Both of these has two variations, linear and that other one.

googling for "where is purple" might show a nice page with links and color diagrams.


Well, all the formats you said there are only formats of storing data in your memory. They are not displayed as they are, but converted to RGB first. Monitors don't know anything but RGB.


The same is true of print formats, but that doesn't mean that they don't have a purpose, I mean RGB is converted to whatever colours the printer has available afterall, you could argue RGB is just as arbitrary in certain circumstances... In fact, in the end you could say that all colour is irrelevant because it's your brain that does the processing in the end and it uses a network of neurons or whatever brains see colour as. That's a bit extreme, sort of a straw-man... But I'm not trying to destroy your point, just trying to contrast it.



Ofcourse they are very useful, never ment to say otherwise. The point is was a little bit offtopic because it was not about why not using that color instead of the other one, but the ordering of colors and the storage space allocated for each color. Beside this, what you've said there is very useful.

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