Goal of this final work is to explain masking in video signal. Beside different types of masking, the influence of masking on quality of displayed video signal had to be explained and explored. Masking is explained as disturbance during observation of target stimulus because of interference of another masking stimulus which is near target stimulus in time and space. Main types of masking are spatial and temporal masking. Spatial masking explains that due to the characteristic of the human visual system, noise (disturbance) in an image is clearly visible on „smooth“ areas of the image while on „rough“ areas it is almost incospicuous. Due to very fast exchange of frames in temporal masking, human eye can't follow all changes that happen and therefore doesn't notice some irregularities at frame exchange in video. Masking effect on the quality of displayed video signal has been studied by conducting subjective and objective evaluation of video. It was revealed that subjective method is more reliable. Namely, subjective method that represents viewers evaluation is more reliable, considering that human eye has the ability to perceive the masking effect while the computer is not capable of such thing.