Information on the YIQ color space

The Applet:

General information on all the color space applets:

All the applets have a button at the top of the applet that says "Click here for more information." Clicking the mouse on that button will take you to a different document that is like this one, that will give more information on that particular color space and that particular applet.
All the applets also display some pictures that try to give the user an idea of where in the color space they are, and what the particular color space looks like.
They all have three slider bars near the bottom that control the three parameters for the color space, though some also have other controls to manipulate their parameters. To the right of each slider bar is a label telling the name of the parameter (such as R for Red in the RGB space, or L for Luminance in the CIE Luv space) as well as showing the current value of this parameter.
There is a rectangle at the very bottom of the applet that shows the color the current parameter values for the color space define.
Some applets also have an area for a message below this rectangle, which will print out a message if the user generates a color in this color space that is undisplayable on the monitor, because the RGB translation of the current parameters gives one or more values outside the proper RGB range [0,1].
If you choose to have more than 1 applet running (by picking more than 1 color space from the initial screen), then when one applet is modified, the other applets modify themselves to show the same color. With this, you can see better how different color spaces relate to one another.
I think it's very informative when having more than one applet running, to put one or two of a color space's parameters at 0, and manipulate the other to see how that specific parameter moves you around in this space and whatever other space(s) you have running. For example, when running the RGB and CIE LUV color space applets, moving the R, G, or B scroller of the RGB applet around, with the other two set at 0 seems to give a decent impression of the shape of the CIE LUV color space.

Specific information on this color space's applet:

The Y parameter has the range [0,1], the I parameter has the range [-0.523,0.523], and the Q parameter has the range [-0.596,0.596].

The two pictures shown in the applet are pictures of the RGB cube when converted into the YIQ color space. The leftmost picture in the applet is a picture of the RGB cube as seen from the Q-axis, with the Y-axis pointing upwards and the I-axis pointing towards the right (these pictures are shown to the left here). The picture on the right is a picture of the RGB cube as seen from the I-axis, with the Y-axis pointing upwards, and the Q-axis pointing to the left (to conform to a right-handed coordinate space). I produced these pictures with a simple raycaster-type program I wrote that will display the RGB color cube in different color spaces.

As the Y, I, and Q values are changed via the scrollbars (or another color space applet), a white dot with a blue outline will move to indicate the current position in this color space.

Some interesting things to notice:
  • The Y parameter roughly corresponds to lightness or illuminance, and so changing the Y parameter basically changes the shade or tint of the color. (See the blurb below about compatibility with black-and-white television.)
  • The I parameter seems to mimic mostly shifts from blue, through purple, to red colors (with increasing I), and the Q parameter seems to mimic mostly the value of green. This is just a rough idea only, that I've acquired through running these applets.

    The YIQ color space:

    More Information:

    The YIQ model is used in U.S. commercial color television broadcasting and is a recoding of RGB for transmission efficiency and for downward compatibility with black-and-white television. This compatibility is that black-and-white televisions only pay attention to the Y-component of the transmission, which contains relative illuminance information. This Y-component is defined to be the same as the CIE Y component (see here for more information on CIE color spaces). This component gets the majority of the bandwidth in television broadcasting, and is thus more precise, such that black-and-white television pictures usually appear sharper than color television pictures in the U.S. Note that it (the Y parameter) gets more of the bandwidth because the human visual system is more sensitive to changes in luminance than to changes in hue or saturation.

    The YIQ color space, like RGB and HSV, is a device-dependent color space, meaning the actual color you see on your monitor depends on what kind of monitor you are using, and what its settings are. However, it is callibrated to NTSC monitors (as the applet above), because televisions (unlike computer monitors) are callibrated to a certain specified standard.

    The YIQ model is a 3D Cartesian coordinate system, with the visible subset being a convex polyhedron that maps into the RGB cube (as shown in the pictures of the applet).

    Y is used as the name for the luminance parameter because Y is typically the letter used to represent luminance (as in the CIE xyY space). The I and Q parameters are named in relation to the modulation method used to encode their carrier signal.




    Links:

    The Color Science & Technology page in the U.K., with links to organizations and resources on color science.
    An abstract on using different color spaces to choose colors.
    Here is a link to a color space FAQ.



    Back to the main color space applet page.