What is Color Gamut and a Wide Gamut Monitor?

By Sareesh Sudhakaran

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Gamut means ‘the complete range’. A color gamut is the complete range of colors in something.

‘Something’ usually means either:

  • The complete range of actual colors in a photograph
  • The complete range of actual colors a device can use or show
  • The Jujube Problem

    Let’s say we have to fill three shipping boxes full of jujubes. Each box is a different size – the biggest one is for our boss while the smallest one is for our best friend. We’re sure both will understand.

    Jujubes

    Image Courtesy: Glane23


    We contact the Jujube Corporation to supply us with these delicious candies in every color it comes in. The Jujube Corporation produces jujubes in 31 colors. They proudly tell us they have and need only three machines, supplying one coloring each – Red, Green and Blue. By mixing these colors in varying proportions they are able to produce 31 different colors.

    We jump in excitement when the Jujube Corporation truck pulls up and the Mr. Jujube himself delivers one big bag full of jujubes in 31 colors. They’ve mixed all the colors!

    We’re not going to let that spoil our day, so we accept the package gracefully and dump all the jujubes on a table. We line up the boxes and fill each one till they’re all full.

    A few jujubes are left behind on the table. Little mercies.

    The color gamut of the jujube Corporation is 31 colors. This is the gamut of the human eye – all the colors it can actually see in reality. A person who is colorblind (or visually challenged) has a smaller gamut than one who is ‘average’.

    Each box can be a computer monitor, a camera, a smartphone, a piece of paper or anything. The box represents any device or thing that has anything to do with real colors.

    Even though the average human can see millions of colors, boxes (devices) need not see all of them. Each box need not show the same color as every other box, just as no two humans share the exact same color gamut.

    The difference between a color model, a color space and the color gamut

    In our analogy, this is how things compare:

  • The RGB machine is the color model, which as we have learned in Color, Color Bit Depth and Color Model, is based on the human eye.
  • The entire range of colors produced by the corporation is the gamut of the human eye. Our eye, as we have seen in Driving Miss Digital, can see about 10 million colors.
  • The size of each box is the color space – which, as we have seen in Color Space, is a theoretical limit (or space) imposed on a device or object. Obviously, our box analogy is not strictly correct, because each box can hold 31 jujubes of one color each. But you get the idea – a color space can theoretically hold a certain range of colors, but in practice that might not be true.
  • The actual range of jujubes in each box is the color gamut of that box. If one box has only 29 colors, then that’s its gamut. The second and third boxes could have more or less, and so it goes.
  • Takeaways:

  • Two monitors can both claim to display sRGB, but they might look different (assuming every other factor is constant) if their actual gamuts are different.
  • This happens because monitors are designed using physical materials, just like our eyes. They behave in certain idiosyncratic ways as far as colors are concerned. This is the fundamental reason why LCDs are different from plasma monitors, and LEDs are different from LCDs, and all of these are different from CRTs.
  • Two broadcast monitors, each producing 100% of a color space, say Rec. 709, is expected to show similar imagery with an image in that color space. If they don’t, one or both of those monitors are not what they claim to be.
  • Two different cameras, both shooting Rec. 709, will show different colors because their sensors have different gamuts – assuming everything else is constant. This is the fundamental reason why CCDs have a different color look to CMOS sensors, or why Foveon sensors seem to have different colors than Bayer-array sensors. It is also why film is so different from digital sensors – the colors of chemicals are different from the colors of semiconductors, among other important differences.
  • Don’t forget – colors are just sensations produced in our brain. Our acceptance of black and white imagery, pencil art and other such imagery shows clearly that color is not everything.
  • NEC Wide gamut display monitor

    The gamut of a photograph

    Apart from what a display or camera can show, a photograph also has limitations. A printed photograph or a polaroid, for example, will show different colors due to the nature of its materials and chemicals.

    A digital photograph is not constrained by physical objects, but by mathematical and  ‘genetic’ ones. The genetic ones are deficiencies passed on to it from camera sensors, processing and circuitry.

    E.g., if you shoot a photograph in Adobe RGB (a larger color space), you are bound to collect some colors that are outside the scope of sRGB. The camera sensor is able to do this because it has a gamut greater than sRGB. This photograph is said to be in a different color space (defined by Adobe RGB), but it also has a gamut (the actual colors within this space that the sensor and camera electronics was able to put into the digital file).

    If this photograph is viewed on a monitor displaying sRGB, then the colors will look off. That’s because the mathematical basis of one color space is different from another. For simplicity’s sake, even though this doesn’t happen in practice, let’s say if we are able to normalize these two, you’ll see your photograph, but with some colors missing. These are the colors that are defined under Adobe RGB but are beyond sRGB.

    The story doesn’t end here. The above is only possible if the monitor itself shows sRGB in its entirety. If it’s a cheap consumer grade monitor that can only show 90% of sRGB, then you’ll find more colors missing from your precious photograph. They’re still there in the file, mind you, but your monitor is unable to show them.

    The following is a list of display technologies in descending order of gamut ability:

  • Laser projector
  • DLP Projector
  • Film
  • LED/LCD/CRT Monitors
  • Consumer television
  • Paint
  • Printing
  •  
    Note: The most modern professional LED display technology goes past CRT in color gamut. That, and the fact that the latter is also power-hungry and large in size, is fueling its march into obsolescence.
    Dolby Monitor

    What is a wide gamut monitor?

    Wide, wider or widest? It doesn’t matter. A wide gamut color space (see where the confusion is born?) is a color space that supposedly has more colors than the human eye.

    A wide gamut monitor purportedly displays more colors than the human eye can see. With today’s technology, that is a boast at best. True, there are certain colors produced by a monitor that the eye might not be able to see, simply because these are two physical things, as explained above.

    There are many advantages of working in a larger color space, just like a bigger arena gives more room for maneuverability. But as far as I know, there is no point in having a device with a gamut larger than the eye can see. Who’s it for?

    The way in which this term is used in the marketplace makes it look like its something else. It’s not. It’s more marketing than scientific truth, so don’t read too much into it.

    Tomorrow they’ll start selling wide-gamut jujubes. Don’t you believe it.

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    December 30, 2012

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