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The Black Offset level you set also becomes the minimum picture level when you lower exposure,
either using the Global Exposure changes, or when you use any of the “darkening” zone controls such
as Shadow, Dark, and Black. The following image shows the result of lowering Global Exposure; the
shadows of the image are compressed more heavily than the highlights as exposure is lowered, with
the result that the minimum value of the image remains at the Black Offset level you set. With shadow
detail impressively preserved, this compression rolls off smoothly and nonlinearly through the
midtones so that the image continues to look as natural as possible.
(Left) Before, (Right) After lowering Global Exposure to compress image contrast down to the
Black Offset level; notice the signal never goes lower than the Black Offset level
This is also true when using other darkening zone exposure controls, such as the Shadow control,
which selectively pushes the exposure of the darker part of the image down, while leaving the
highlights alone. While reducing Shadow exposure, the darkest pixels still compress so that nothing
goes beneath the Black Offset level you set.
Bottom line, you can adjust Black Offset at any time, either before or after any other Global or Zone
adjustments, to fine tune the image as necessary.
Making Zone-Based Adjustments
After you’ve made whatever initial global adjustments you want, you can optionally make more
tonally-specific adjustments to the image via the Zone-based color and contrast controls to the left.
These divide the image into multiple overlapping “zones,” which are somewhat similar in principal to
Ansel Adams’ zone system, which divides images into tonally-specific regions based on image
luminance, from pure black, through progressively lighter shadows, to 18% gray as the middle value
centering the midtones of most images, and then up through progressively lighter highlights on the
way to the last zone of pure white.
Simplified illustration of Ansel Adams’ zone system
While Adams’ zone system was meant to teach people how to think about using the available range of
the photographic medium when exposing images, the zones of the HDR palette let you put this
concept into practice by allowing you to make tonally-specific Color Balance, Saturation, and Exposure
adjustments that only affect the range of shadows or highlights that fall within that zone.
Chapter 129HDR Palette 2594
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