Rendering y´cbcr footage in the rgb color space, Choosing rgb versus y´cbcr color space, Compositing in y´cbcr and rgb color spaces – Apple Final Cut Pro 6 User Manual
Page 1449: Rendering y´c, Footage in the rgb color space, Choosing rgb versus y´c, Color space, Compositing in y´c, And rgb color spaces
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Part IV
Rendering Y´C
B
C
R
Footage in the RGB Color Space
When super-white Y´C
B
C
R
values are converted to RGB, any values above 235 are
mapped to 255. Any variation in luma above 235 is therefore clamped, or clipped,
resulting in solid patches of white where there was once detail in the bright parts of
the image. If these RGB values are converted back to Y´C
B
C
R
, all white values of 255
are mapped to a single value (usually 235, which is white in Y´C
B
C
R
). The newly
converted white values are lower than the white values originally captured, causing
areas of the picture that had super-white values to darken slightly and to appear flat
where there was once detail in the highlights. This is known as luma clamping. You
can avoid this by editing your Y´C
B
C
R
footage natively in the
Y´C
B
C
R
color space.
Choosing RGB Versus Y´C
B
C
R
Color Space
Each color space has a certain range, or gamut, of colors that can be represented.
Some colors represented in the Y´C
B
C
R
color space cannot be represented in RGB and
are said to be out of gamut. If the color space of your media files doesn’t match the
color space of your sequence, Final Cut Pro maps the media file color values to the
color space of the sequence. In some cases, colors get “clipped” to the nearest value
during conversion. This can cause very saturated colors to become less intense and is
referred to as chroma clamping.
Compositing in Y´C
B
C
R
and RGB Color Spaces
Many compositing operations in Final Cut Pro work the same way in Y´C
B
C
R
as they
do in RGB. However, in some cases, slightly different results may occur. This is because
the Y´C
B
C
R
and RGB color spaces are not identical, and some compositing operations
that generate highly saturated colors may show different clamping behavior in Y´C
B
C
R
than they do in RGB.
For example, using the Add composite mode to combine 75 percent cyan and
75 percent white will “clamp” to white in RGB, but to a bright cyan color in Y´C
B
C
R
. For
this reason, it’s important to verify the results of the composite by doing a test render
in the color space you will do the final render in.
For more information about limiting Y´C
B
C
R
and RGB values, see “