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Appendix A | Appendix B | Appendix C | Glossary | Index | Legal Stuff | License


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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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