In fact, our measurements show that both luminance and chrominance vary too, so that colour changes are more a matter of shade changes, rather than differences in hue. Delta E combines the effects of differences in both hue and brightness, so our Delta E results represent colour differences across each panel's surface. The biggest differences between any two measurement points are over 20 Delta Es, more than four times the visible threshold. Average Delta Es between any two adjacent measurement points are also high, at between 6 and 14. In practice, large changes in Delta E appear as either dark or bright patches on an all-white display, as obvious colour changes or as a mixture of both.
Visible changes are evident more as darker or lighter areas.
Contrast ratio Contrast ratio is the ratio between the peak white level and the black level of a display. Although it's relatively easy to set peak white so that the gamma curve doesn't clip, it's much harder to set black level accurately, because it falls at the shallow end of the gamma curve. One of the weaknesses of LCD monitors is that they tend to leak a significant amount of light from the backlight, even when displaying a full-black screen. Colour gamut Gamut is the range of colours a display can produce. Plotted into a colour space, display gamut always takes the form of a triangle, with the display's version of the primary colours red, blue and green at its points.