The Intensity Scale (sometimes called the Gray Scale) not only controls the contrast within all displayed images but it also controls how the Red, Green and Blue primary colors mix to produce all of the on-screen colors. The steeper the Intensity Scale the greater the Image Contrast and the higher the saturation of displayed color mixtures. So if the Intensity Scale doesn't follow the Standard that is used in all consumer content then the colors and intensities will be wrong everywhere in all images.
In order to deliver accurate color and Image Contrast a display must closely match the Standard Intensity Scale. Figure 3 shows the measured Intensity Scales for the displays alongside the industry standard Gamma of 2.2, which is the straight black line.
The iPad mini has a fairly straight and accurate Intensity Scale, which produces fairly accurate Image Contrast. However, it hovers 5 percent over the Standard Intensity Scale. That produces a 5 percent compression in the Intensity Scale near the 100 percent Peak Intensity. That tends to reduce the Image Contrast and Color Saturation for bright image content. For example, it was apparent in photos of brightly lit faces, which appeared slightly washed out in the Viewing Tests.
The iPad 2 also has a straight Intensity Scale but it is much steeper than the Standard. That improves Color Saturation, which helps with the iPad 2's smaller Color Gamut.
The Nexus 7 has a very inaccurate curved Intensity Scale that reduces Image Contrast and Color Saturation. The critical area near Peak Intensity on the Nexus 7 is discussed in greater detail in this Display News article.
The Intensity Scales for the Amazon Kindle Fire HD and new iPad are not shown in the Figure below because they are close to the Standard and would interfere with the iPad mini Intensity Scale. Refer to this Figure for their Intensity Scales.