Primary Color Correction: Tonal Range Primer - The Art and Technique of Digital Color Correction - page 20

light reflects in growing intensity on the curve of the bag then falls away
on the right side of the curve. The speckled area above the steep spike
appears to be the portion of the yellow rectangle at the top of the bag.
I can basically confirm this suspicion by looking at the YRGB parade.
If you look at the same horizontal area on the YRGB display
( Figure 1.20 upper left corner )—the first of the three spikes—you will
notice that the spike is taller in the red and green cells and shorter in the
blue cell. I'll explain this in more detail in an upcoming sidebar, but the
equal combination of red and green in RGB colorspace makes yellow. Now
the yellowish nature of the spike is certainly partly due to the fact that the
highlight on the bag is slightly yellowish, but the difference between the
amount of red and green compared to blue at that point doesn't corre-
spond to just a small yellowish tint to the highlight. It indicates something
that is quite yellow, like the rectangles at the top of the punching bag.
Continuing on across the waveform from left to right, there are a
four grayish spikes leading up to a thick spire that sits about one-third
of the way across the image. These smallish spikes are the highlights in
the wrinkles at the top of the punching bag: one along the seam in the
middle of the bag and three short, but bright highlights just to the left of
the other yellow rectangle. The tall spear in the waveform is the bright
highlight at the top of the right side of the bag. Notice that in the tall
spear, the discrepancy between the height of the red, green, and blue cells
is minimized, because the yellow of the rectangle is obscured both by the
bright highlight and in shadow. Your brain tells you that this has to be the
same color yellow as the rectangle on the other side of the bag, but if you
just look at the right-side rectangle, it's very difficult to make out any real
yellow tint.
After the spike from the right-side bag highlight, there is a slightly
elevated band in the waveform that goes between about 2 or 3IRE up to
about 20IRE. (On the YRGB Parade, it goes from about 15 millivolts to
about 150 millivolts if you use the measurement scale to the left, which
goes from -300 to 800.) This band corresponds to the light caught by the
atmospheric smoke between the boxer and the bag.
The complex shape to the right of that is the boxer. The highest por-
tions of this shape indicate the reflected highlights from the top of his
rear boxing glove, head, neck, shoulders, and left tricep. There are also
bright portions indicating his white shirt, reflections on his pants, and
the brighter flesh of his chest and forearm. The heavy band at the very
bottom of the waveform is the shadow of his pants. On the right side
of this shape, it falls off precipitously, with only a small ramp around
40-50IRE ( Figure 1.19 c ). I think that ramp is the highlight from the top
of his back leg.
The rest of the waveform display to the right is the bright haze of
smoke. The top of the band is the bright smoke at the top of the picture

D e f i n i t i o n
IRE: One of the units of
measurement that can
describe a composite ana-
log video signal's ampli-
tude (brightness), where
0IRE generally represents
black and white extends
to +100IRE. 1IRE is equal
to 1/140 of a volt or 7.14
millivolts in NTSC, though
in all other systems, it
corresponds to 7 millivolts.
IRE stands for the Institute
of Radio Engineers, which
defined the unit.