Quezi

Color fringing around thin black verticals (photo by chrisdlugosz - CC-BY)

On some computer monitors, color fringes appear around narrow lines, or may appear and disappear as you move the cursor over small text. To see why this happens, we need to consider how the screen is constructed.

Computer screens, regardless of whether they are Liquid Crystal Displays (LCD), Cathode Ray Tubes (CRT) or Light Emitting Diodes (LED), represent colors using tiny colored

dots called pixels. A common arrangement is for each pixel to consist of a group of sub-pixels in the primary colors: red, green and blue (RGB).

If the pixels of the same color are in-line vertically, and part of the display is black (i.e. not lit up), the visual effect will depend on how many columns of pixels are not lit up. If a multiple of three columns is unlit, then each of the primary colors is extinguished to an equal degree, and our eye is likely to perceive a black stripe.

However, if the black part of the display covers something other than a multiple of three columns, the sub-pixels of different colors will be unlit in different proportions. This unbalances the color mixture of the remaining lit sub-pixels. For example, if a thin cursor covers a green column and a blue column but not a red one, our eye is likely to perceive some red fringing at the edge of the cursor.

The effect is not so noticeable on the latest monitors, which usually have their pixels closer together.

Related questions:

• How will self-driving cars change the world?
  Researchers at Google and elsewhere have been having great success with self-driving cars. These cars have already driven hundreds of thousands of miles without being controlled by a human driver. It...
• What Will the Internet of the Future Look Like?
  What is the future of the Internet? If you were to put any stock in my predictions of the future, we’d all have flying cars and robot butlers by now. So far be it from me to make any guesses what the...
• What is source code?
  how to get your ex back (This is a guest post) When we run an application on a computer, the computer "knows" what to do by stepping through a sequence of instructions. These instructions are ve...
• Where the ### is the hash key on a UK Apple Mac keyboard?
  If you want to type the hash character ('#', also called 'pound' in some parts of the world) on a UK Apple Mac, you can look everywhere on your keyboard and you won't find the hash symbol. If you ...
• What would it look like to fly over Mars?
  What would it look like if we could fly above the surface of Mars in a jetliner and look out of the window? Of course a regular plane can't fly in the thin atmosphere of Mars, so this is a hypothe...