The vectorscope is a type of oscilloscope used to visualize the chrominance subcarrier of a video signal. Originally used to measure and test analog television signals, the vectorscope reveals the relationship between the two colour difference components. For digital video formats, the vectorscope plots Cb and Cr chrominance components.
For more information: https://en.wikipedia.org/wiki/Vectorscope
The Vectorscope Image Analyzer is an interactive exploratory environment to observe the underlying chrominance information of images. The function supports most RGB images, and can plot both discrete Cb-Cr points or a simulated analog trace on an NTSC graticule. The trace is updated in real time, seeing the hue information change as the region of interest is resized and moved.