About rec-601 and rec-709 color standards – Apple Final Cut Pro 5 User Manual
Page 1339
552
Part III
Output
Rendering Y´C
B
C
R
Footage in RGB
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. When 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 less 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. For
example, the Apple DV codec is capable of processing in Y´C
B
C
R
color space,
eliminating clamping and preserving super-white video levels in rendered and
unrendered material.
For more information about white and super-white levels, see “
Compositing and the 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
then
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.
About Rec-601 and Rec-709 Color Standards
High definition video formats such as DVCPRO HD often use colors defined by ITU-R
BT. 709, or Rec-709. Standard definition formats use a color space defined by ITU-R BT.
601, or Rec-601 for short.
Final Cut Pro automatically handles both color standards, and accurately converts from
one standard to another when you mix formats. For example, if you edit a standard
definition DV clip into a sequence that uses a DVCPRO HD preset, the standard
definition media is properly converted from Rec-601 to Rec-709. High definition video
used in a standard definition sequence is also converted properly from Rec-709 to
Rec-601.