In a pixel on an LCD monitor, the amount of light that is transmitted from the backlight depends on the voltage applied to the pixel. For the amount of light, it doesn't matter whether that voltage is negative or positive. However, applying the same voltage for a long period would damage the pixel. Do you remember how electricity decomposes water into oxygen and hydrogen gas in chemistry class? Similar things could happen inside the liquid crystals that are in the pixels. In order to prevent damage, LCD displays quickly alternate the voltage between positive and negative for each pixel, which is called 'polarity inversion'. Ideally, the rapid polarity inversion wouldn't be noticeable because every pixel has the same brightness whether it a positive or a negative voltage is applied. However, in practice, there is a small difference, which means that every pixel flickers at about 30 hertz. In order to make this less noticeable, pixels with positive and negative voltages are interleaved, such that on average the screen as a whole keeps the same brightness – at least for normal images. The interleaving does not work for the inversion test images, at least for the one(s) where the pattern matches the interleaving pattern of the monitor. In such cases, the monitor will flicker if the positive and negative voltages are not tuned very well.....