In an (M) NTSC or (B, D, G, H, I) PAL video signal, the luma (black and white) and the chroma (color) information are combined together. If you want to decode the video signal, the luma and chroma must be separated. The chroma trap is a method for separating the chroma from the luma, leaving the luma relatively intact. How does this work? The NTSC or PAL signal is fed to a bandstop filter. For all practical purposes, a bandstop filter allows some types of information (actually certain frequencies) to pass through but not others. The bandstop filter is designed with a response, or stop, to remove the chroma so that the output of the filter only contains the luma. Another name for a bandstop filter is a trap. Since this trap stops chroma, it's called a chroma trap. The sad part about all of this is that not only does the filter remove chroma, it removes luma as well if it exists within the region where the stop exists. The filter only knows ranges and, depending on the image, the luma information may overlap the chroma information. The filter can't tell the difference between the luma and chroma, so it stops both when they are in the same range. What's the big deal? Well, you lose luma and this means that the picture is degraded somewhat. Using a comb filter for a Y/C separator is better than a chroma trap or chroma bandpass. See the chroma bandpass and the Y/C separator definitions.