PAL Colour Bar Test Pattern
(with a "Bucket of Blood")
Colour Bars are used to callibrate video and television monitors. The example above is a common type of PAL colour bar test pattern. The red bar at the bottom is often referred to as a bucket of blood and may contain some text identifying the source.
Colour Bars are usually generated by specialised video calibration equipment such as a synch pulse generator, or by a video camera.