![]() ![]() MagicQ approximates it’s shape by modelling it as a set of flat planes in reality, it is somewhat concave, meaning that MagicQ may overestimate what a fixture’s brightest colours really are. One challenge to colour matching is that finding the shape of this "ceiling" is a difficult process. If one sets the colour picker to a certain colour (e.g: x=0.625, y=0.314), and the brightness to 50%, this means "50% as bright as the brightest colour that can be produced with (x=0.625, y=0.314)". The "ceiling" of that shape represents 100% brightness these are the brightest versions of all the colours that the fixture can make. If one thinks of the three-dimensional gamut shape above, the "floor" (Y=0) represents both 0% brightness and 0 luminosity. The definition used by the colour picker is dependent on a particular fixture’s gamut. "Brightness", on the other hand, has no strict definition. Luminosity is the scientific measure of the intensity of a light source, regardless of its colour it can be measured with a light meter, giving a value in lux. The different meanings of "brightness" and "luminosity" should be noted carefully. Michael Horvath (SharkD), Christoph Lipka / Wikimedia Commons / CC BY-SA 4.0 Green is the brightest emitter by far, and so cyan and yellow have a very high luminosity compared to magenta. Note the corners that can be seen for the red and blue emitters (green is at the back), and again for cyan, magenta and yellow. To illustrate, below is a representation of all the colours that can be produced by a normal sRGB computer monitor. The Y axis is scaled to the luminosity of this white, so it is always at Y=1. The bottom surface (Y=0) is all black the very peak of this shape is the source’s "white" - which you get if you have all the emitters set to 100%. Plotted in 3D CIE 1931 space, this forms a roughly polyhedral shape all colours inside this shape can be made. You can measure a light source (such as a fixture) to determine the exact colours each emitter gives off this process is called colourimetry.įrom these colours, one can determine the range of all possible colours that a light source can give this is called that source’s "gamut". This is because no matter how hot an object is heated, it will never give off saturated blue light the temperature axis ends at "infinity kelvin", which is a deep sky blue colour. This colourspace cannot produce deep blues or cyans. There is a rough correspondence between plus/minus green gels and delta-UV a one-eighth gel is about 0.004 UV, a one-quarter gel is about 0.008 UV, and so on. Using this channel allows for reds, oranges, yellows, pale greens, pinks, and purples to be achieved. The practical effect of this is that a positive delta-UV is similar to "add green", and a negative is "subtract green", similar to colour gels made for the same purpose. This measures the distance from the Plankian locus in a different CIE colourspace (CIE UV), either upwards (positive values) or downwards (negative). The delta-UV value is used to produce colours other than "whites". The colours that can be achieved this way fall along a curved line in CIE 1931 space, called the "Plankian locus". For instance, heating an object to about 6500K will cause it to glow a bright white the colour of a clouded sky. The temperature of a "white" colour is defined as what temperature an object would need to be heated to start giving off that colour. The two values are temperature (in Kelvin), and Delta-UV, (in UV units).Īs objects are heated, they begin to glow different colours. The CCT colour space uses correlated colour temperatures. One advantage of CIE 1931 is that mixing any two colours on a CIE chart will produce a colour along the straight line that joins them (unfortunately, an equal mix is not guaranteed to be in the middle). ![]() Under HSI models, they can be thought of as colours with over 100% saturation. These are "impossible" or "forbidden" colours, and they exist only theoretically. Points outside of the horseshoe shape of a CIE chart correspond to colours that could be "seen" if specific signals were given to the brain, but these signals can never be given by the human eye (under normal circumstances). Note that not all combinations of x and y are real colours perceivable by the human eye. These coordinates are independent of any device, and form a three-dimensional space of potential colours. This measures the colour of a light source using two coordinates, x and y, and the brightness with a third, Y (capital). For this reason, colour scientists use a more general model to describe colours: CIE 1931. One limitation of the above models is that they are defined based on a set of primary colours, which may vary between devices (for example, how red is the "red" in RGB?).
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