1.5

The Q Bar
The Q bar shows the proper angle at which the hue of the purple box in the color bars
test pattern should appear. This purple box, which is located at the right of the 100-percent
white reference square, is referred to as the +Quadrature signal, or Q for short.
When troubleshooting a video signal, the correspondence between the Inphase and
+Quadrature components of the color bars signal and the position of the –I and Q bars
shows you whether or not the components of the video signal are being demodulated
correctly.
The Histogram
The Histogram provides a very different type of analysis than the waveform-based scopes.
Whereas waveforms have a built-in correspondence between the horizontal position of
the image being analyzed and that of the waveform graph, histograms provide a statistical
analysis of the image.
Histograms work by calculating the total number of pixels of each color or luma level in
the image and plotting a graph that shows the number of pixels there are at each
percentage. It’s really a bar graph of sorts, where each increment of the scale from left
to right represents a percentage of luma or color, while the height of each segment of
the histogram graph shows the number of pixels that correspond to that percentage.
The RGB Histogram
The RGB histogram display shows separate histogram analyses for each color channel.
This lets you compare the relative distribution of each color channel across the tonal
range of the image.
198 Chapter 8 Analyzing Signals Using the Video Scopes