The Effect of Missing Values on Tonal Gradation

Although the following tonal scale is visually continuous, in reality it is composed of 256 values.  The following charts show the effects of introducing gaps between tone steps.

The next scale shows the effect of skipping every other tone:

In the following, posterization becomes visible:

Using Color Channels to Detect Tone Gaps

Since the luminance and RGB histograms are composites of the image's red, green, and blue components, gaps tend to be filled and the contours smoothed in forming them.  This may mask problems.

In critical cases, problems with gaps and noise are more easily detected by examining the underlying color channels.