Chapter 18 - The Adjust Tab
Gamma Adjustment | Cross-Platform Gamma Issues |
Brightness | Contrast | Black Restore |
White Restore | Hue | Saturation
The Adjust tab lets you change the image of
your final output movie, such as alter its gamma,
hue, brightness, etc. In order to immediately see
the results of your adjustments, open the Dynamic Preview window from the Windows menu.
NOTE: All of these adjustments change
the actual values of the pixels these
adjustments can't be undone later. None of the
architectures or codecs currently allow for dynamic
image adjustments. For example, there is currently
no way to make the same movie play lighter on a PC and darker on a Macintosh.
Gamma Adjustment
This allows you to adjust the gamma of your image. Adjusting the gamma of your
image modifies the gray values in a nonlinear
fashion while leaving the black and white values
relatively unmodified. It is similar to adjusting the brightness and contrast simultaneously. Using
the gamma adjustment to change the image density
is usually preferable to using the lightness and contrast controls, because moderate
gamma changes don't normally destroy the detail in highlights and shadows. This is due to the fact
that most of the changes occur in the mid-range tones.
Go back to the top of the page
Cross-Platform Gamma Issues
Gamma adjustment is useful for lightening
movies to compensate for the darker monitors of Windows machines. The number you specify
on the Gamma slider changes the gamma curve of the final image numbers greater than 1
make the image lighter, numbers less than 1 make
it darker. Generally, +30 will compensate for an average
PC monitor. Make sure to check that the result is still acceptable for your
Macintosh platform as well.
If you are authoring a cross-platform CD-ROM,
and don't want to have different versions of the
movies for the PC and Mac, you should select a
gamma setting that looks acceptable on both machines.
Usually, this means your Mac movies end up
looking a little light, and your PC movies look a little dark.
However, this is often better than the alternative
of your Mac movies looking perfect and the PC
movies looking significantly too dark. As a rule of thumb,
we recommend that you set the gamma setting so it looks ideal on your Macintosh screen, then add +30.
This should be an acceptable compromise for both Mac and PC monitors.
Go back to the top of the page
Brightness
The brightness slider makes the image lighter
or darker in a linear fashion. Unlike the gamma setting, increasing the lightness changes all
the pixels the same amount. Thus, your light
tones tend to become totally white when you raise
the brightness, and your dark tones totally black when you lower the brightness.
Go back to the top of the page
Contrast
Adjusting the contrast changes the range of
dark to light pixels in a linear fashion. When you
raise the contrast, the darks get darker and the
lights get lighter. Unlike using the gamma
adjustment, increasing the contrast can "blow out" the
highlights and make shadows totally black. Lowering
the contrast tends to make your image look gray.
Go back to the top of the page
Black Restore
This feature lets you set the "black level" of
your image. Essentially, the black level is the
point below which all pixels are made entirely black.
For example, if you have titles on a black background, that background may actually be
dark gray with some random video noise in it.
Setting the black restore to a moderate level should
make all the dark gray pixels totally black, and
therefore may improve how these titles look.
Used properly, black restore may improve how well some movies compress, because it
can remove visually unimportant image data in very dark areas.
Go back to the top of the page
White Restore
White restore is very similar to black restore, except it affects the light tones of the image.
It works well to "clean up" areas that should
be white, but aren't quite. Like black restore, it
can also improve the compression of certain images.
Go back to the top of the page
Hue
Changing the hue alters the overall color
balance of the image. This is often useful to
compensate for slight color shifts some codecs introduce.
Go back to the top of the page
Saturation
This changes the intensity of the color in your image. Moving the slider to the right
increases the colors, to the left decreases them. Moving
it all the way to the left effectively reduces
your image to greyscale.
Go back to the top of the page