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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<title>Input vs. Output Referred images</title>
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<h2 style="text-decoration: underline; font-weight: bold;">Input vs.
Output Referred Images<br>
</h2>
A lot of Photography related sources recommend that images be
encoded in a large gamut colorspace such as ProPhoto, but don't
explain the implications of doing this in in the process of
subsequently displaying such photo's. <br>
<h3> Input referred:</h3>
Images are encoded in a way that represents their unchanged or
originally captured values, in an encoding space that is larger
enough to store their gamut without clipping. The gamut of the
encoding space tells you nothing about the gamut of the images.<br>
<br>
Typical: L*a*b*, Raw, ProPhoto, RIMM etc.<br>
<h3>Output referred:</h3>
Images are modified (i.e. rendered) to fit within the gamut of a
specific real world output device (such as display or printer). This
means that typically the encoding space is a good representation of
the gamut of the images.<br>
<br>
Typical sRGB, AdobeRGB, printer profile, display profile, etc.<br>
<br>
<br>
Before displaying images that are Input Referred, they need to be
rendered to a smaller gamut. This may be done manually by adjusting
the images carefully to fit within the smaller gamut, or in some
automatic fashion such as by hard clipping them to the smaller
gamut, or by setting up a specific gamut mapping for each image or
set of images that occupy a similar gamut.<br>
<br>
<u><b>Note</b></u> that setting up a gamut mapping from the very
large Input referred encoding gamut to the smaller output device
gamut will almost certainly result in a disappointing loss of
saturation, because the images deliberately do not occupy the large
encoding gamut, and so get unnecessarily squashed down to allow for
colors that they do not actually contain.<br>
<br>
See also Scenarios.html#LP3.<br>
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