User Manual

Table Of Contents
curve) to maximize the efficiency of the bit depth being used, and different cameras
use different gamma curves to maximize the image data from different sensors. Since
the Color Match algorithm converts image data into a scene linear space before
creating an adjustment, it needs to undo the gamma curve created by the camera or
debayering process. If the wrong Source Gamma setting is selected in the Match Color
palette, then the data will not be linearized correctly and the resulting match will be
inaccurate.
Lighting in the scene with an unusual spectral response or a strong color cast can
cause an inaccurate match. Scenes lit with lights that have an unusual spectral
response (such as cheap fluorescent bulbs, or mercury vapor fixtures that exhibit a
very narrow or spiky spectral power distribution) can cause metameric errors in both
the camera’s response and the Color Match function, resulting in the creation of an
inaccurate adjustment. The most accurate results are obtained when the scene uses
lighting with a chromaticity that is close to the black body locus (with a highly correlated
color temperature) and a relatively smooth spectral power distribution. In other words,
use high-quality lighting that doesn’t have spikes in specific parts of the spectrum.
Large differences between the color temperature of the lighting shining directly on the
chart and ambient lighting elsewhere in the scene can cause perceptual errors. Often
the problem is one of perception and not an incorrect color adjustment. For example,
outdoor scenes being artificially lit with instruments shining extremely warm light (low
color temperatures of 3200K or less) but that have cooler ambient lighting may appear
overly blue if matched with a Target Color Temp of 6500K. This happens because the
chart under direct lighting is lit at the lower (yellower) color temperature, but areas of
the scene in shadow are much cooler because of the ambient “blue” light from the sky;
the result is an automatic color adjustment that’s correct for the chart, but exaggerated
in the background.
How to Use Color Match
The following procedure shows how to use the Color Match palette and overlay to create a
color correction.
The Color Match palette
To sample a color chart to make an automatic correction:
1 Select the clip with a chart you want to sample. If necessary, you can use the View >
Show Current Clip With Handles option to show additional frames at the beginning of
the current clip to reveal a color chart in the leader of your media.
2 If necessary, choose an option from the Source Gamma drop-down menu that
corresponds to the gamma with which the media was recorded.
Chapter – 116 Automated Grading Commands and Imported Grades 2631