Apple Final Cut Pro 5 - Manual (Page 1218)

Chapter 20 Color Correcting Clips 431
II
Learning to Read the Histogram
The Histogram display shows you the relative strength of all luminance 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 each pixel on
the scale from left to right represents a percentage of luma, from 0 to 110. The height of
the bar at each step on the scale represents the number of pixels in the image at that
percentage of luminance, relative to all the other values. For example, if you have an
image with a lot of blacks, you would expect to see a spike in the Histogram display
near the luma range of 10 to 20 percent.
The Histogram can be very useful for quickly comparing the luma of two clips so you
can adjust their blacks, mids, 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 may have shifted because of a cloud or change in exposure. You can easily see
such differences on 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 95 percent.
The red area of the
histogram indicates
pixels in the super-
white range.
The position of the spike
represents 15% luminance.
The height of the
spike represents the
number of pixels in
the image at this
percentage (15%) of
luma.
The spike is at 95%.