32 Bits per Channel

32 Bits per Channel

Although it is not necessary to use HDR source to take
advantage of an HDR pipeline, it offers a clear glimpse
of this brave new world. Open 11_treeHDR_lin.aep; it
contains a comp made up of a single image in 32 bit EXR
format used to create . With the Info panel
clearly visible, move your cursor around the frame.
As your cursor crosses highlights—the lights on the tree,
specular highlights on the wall and chair, and most especially,
in the window—the values are seen to be well above
1.0, the maximum value you will ever see doing the same
in 8 bpc or 16 bpc mode. Remember that you can quickly
toggle between color spaces by Alt/Option-clicking
the project color depth identifi er at the bottom of the
Project panel.

Any experienced digital artist would assume that there is
no detail in that window—it is blown out to solid white
forevermore in LDR. However, you may have noticed an
extra icon and accompanying numerical value that appears
at the bottom of the composition panel in a 32 bpc project
. This is the Exposure control; its icon
looks like a camera aperture and it performs an analogous
function—controlling the exposure (total amount of light)
of a scene the way you would stop a camera up or down (by
adjusting its aperture).
Drag to the left on the numerical text and something
amazing happens. Not only does the lighting in the scene
decrease naturally, as if the light itself were being brought
down, but at somewhere around -10.0, a gentle blue gradient
appears in the window ( left).

Drag the other direction, into positive Exposure range,
and the scene begins to look like an overexposed photo;
the light proportions remain and the highlights bloom
outward ( right).
The Exposure control in the Composition panel is a
preview-only control (there is an effect by the same name
that renders); scan with your cursor, and Info panel values
do not vary according to its setting. This control offers
a quick way to check what is happening in the out-ofrange
areas of a composition. With a linear light image,

each integer increment represents the equivalent of one
photographic stop, or a doubling (or halving) of linear
light value.