The Intensity Scale (sometimes called the Gray Scale) not only controls the Image 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 on-screen image contrast and the higher the saturation of all displayed color mixtures.
Intensity Scale Accuracy
So if the Intensity Scale does not follow the Standard
that is used in all consumer content then the colors and intensities
will be inaccurate everywhere in all images.
In order to deliver accurate color and image contrast a display must closely
match the Standard Intensity Scale.
Figure 3
below shows the measured Intensity Scales for the
iPhone XS Max alongside the industry standard Gamma of 2.2,
which is the straight black line.
Logarithmic Intensity Scale
Both the eye and the Intensity Scale Standard operate
on a logarithmic scale,
which is why the Intensity Scale must be plotted and evaluated
on a log scale as we have done below.
The linear scale plots that are published by many reviewers
are bogus and completely meaningless because
it is log ratios rather than linear differences
that matter to the eye for seeing accurate Image Contrast.
Variation with Average Picture Level APL
Figure 3
below shows the variation in the Intensity Scales between
Low APL and 50% APL.
For the iPhone XS Max there is only a small Shift in the Intensity Scales,
with the Gamma varying from 2.30 for Low APL to 2.35 for 50% APL.
As a result, the Image Contrast remains relatively unchanged with APL,
and we then expect the Absolute Color Accuracy to also
have small variations with APL, which is examined in
Figure 4.
The Intensity Scales for the iPhone XS Max are both somewhat steeper than the Standard Intensity Scale.
Gamma is 2.30 for Low APL and 2.35 for 50% APL.
