Apple Final Cut Pro 7 - Manual (Page 1310)

Learning to Read the Histogram
The Histogram shows you the relative distribution of all luma values in the video frame
at a glance, from black to super-white (assuming the video codec you’re using supports
Y
′
C
B
C
R
processing). It’s really a bar graph of sorts, where the x axis represents a percentage
of luma, from 0 to 110 percent. The height of the line at each step on the scale represents
the number of pixels in the image at that percentage of luma, relative to all the other
values. For example, if you have an image with a lot of black pixels, you would expect to
see a spike in the Histogram near the luma range of 10 to 20 percent.
The red area of the
histogram indicates pixels
in the super-white range.
The position of the spike
represents 15 percent luma.
The height of the spike
represents the number
of pixels in the image
at this percentage
(15 percent) of luma.
The Histogram can be very useful for quickly comparing the luma of two clips so you can
adjust their blacks, midtones, and whites to match more closely. For example, if you were
matching an insert (or close-up) clip to the clip shown above, the overall luma levels
might have shifted because of a change in lighting or exposure. You can easily see such
differences in the Histogram and correct for them. For comparison, the image below has
a lot of whites, so the Histogram shows a cluster of values at the high end of the scale,
with a spike at 96 percent.
The spike is at
96 percent.
1310 Chapter 78 Measuring and Setting Video Levels