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664 Chapter 20: Managing Scenes and Projects
Histogr am—This graph shows the image’s
luminance values in a logarithmic scale. The red
lines indicate the current Black Point and White
Point values.
Thegraphisvisibleonlyforluminancelevels
with substantial representation in the image. In
other words, if a luminance level only applies
tooneortwopixelsintheimage,therewillbe
no corresponding graph line on the histogram.
Compare with Measured Min/Max, which gives
theentirerangeofluminancelevelsintheimage.
Ingeneral,theresultingimagewillhavethemost
dramat ic effect when the histogram is used to set
theBlackPointandWhitePointrangevalues,
rather than using the ful l range expressed by
Measured Min/Max.
Exposure group
Black Point—When this option is turned on, y ou
can set the luminance value that you would like
to be treated as the darkest color, or “black”. The
value can be set as a logar ithm (Log) or as a linear
value (Linear). Al l values below this value will be
clamped to black. When this o ption is turned off,
thelowestpossiblevalueisusedastheBlackPoint.
Measured Min/Max—Displays the actua l minimum
and maximum luminance values in the image,
expressed as both the logarithmic and linear
values. Using these values for the Black Point
andWhitePointwillresultintheimage’sfull
luminance range being used. However, the
histogram might show that the majority of the
luminance levels fall into a much smaller range.
White Point—Sets the luminance value that you
wouldliketobeconsideredthebrightestcolor,
or “white”, either as a logarithm (Log) or linear
value (Linear). All luminance values in the image
thatareabovethisvaluewillbeclampedtowhite.
White pixel values inside HDR files can be much
larger than a Linear value of 1.
The image’s extended luminance range is used
only when the White Point’s Linear value is set
above 1.0. In other words, setting White Point at or
below a Linear value of 1.0 will not use any of the
HDR image’s special luminance prop ert ies, and
will give results similar to other bitmap formats
such as TIF and JPG.
Log—Sets the Black Point or White Point as a
logarithmic value ranging from –128 to 127.
Changing this value changes the Linear parameter
to the corresponding value.
Linear—Sets the Black Point or White Point as
alinearvaluerangingfrom0toover1trillion.
Changing this value cha nges the Log parame ter to
the corresponding value.
Preview window—Displays the selec ted HDR
image.
Internal Storage group
Rea l Pi xels (32 bpp)—Compresses the luminance
selections into a color space w ith 32 bits per pixel.
PremultipliedAlphaandMotionBlurdonotwork
w ith this option.