The second is frequency error. A frequency error is when the pixel clock produces the wrong sampling frequency. At the beginning of the scan line, this error is non-existent or small. By the end of the line, however, the error has compounded and can be significant. The third problem is what is specifically termed pixel jitter.
Pixel jitter is an individual sampling, or per pixel, error caused by the pixel clock.
A Small Error Can Have Dramatic Results These errors in timing results in inaccurate data representing brightness. As stated, even a slight variation in the time of sampling can create large differences in the resulting brightness value for a single pixel. This is especially true during the rise or fall of a wave, where the miscalculated value is magnified, as shown in the figure to the right. Also consider we've been discussing only one scan line. When the signal gets to the next scan line in microseconds, any pixel jitter will be exaggerated.