PRG Mbox - Page 168

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MBOX® USER MANUAL
Pre-Multiplying Alpha
The Mbox File Convertor has one additional function: it can apply pre-multiplied alpha to a TIFF or PNG le that was
created using straight alpha. This can help to reduce fringing around the edges of these les if they were created
improperly. When pre-multiplying alpha in still image les, there is no conversion of le-type or quality adjustment.
When pre-multiplying alpha, the color (red, green, and blue) value for each pixel is multiplied by that same pixel’s alpha
value. Each of these values range between 0.0 and 1.0, where 0.0 is none, 1.0 is full. Therefore, when using pre-
multiplied alpha, a pixel with an alpha value < 1.0 (i.e. it has some amount of transparency) will be rendered with the
intensity of its color values reduced. This is very useful for reducing the white or gray fringe seen around some objects in
content that uses an alpha channel.
File Conversion Procedure
Step 1. Locate the Mbox File Converter application in the /Applications/Mbox v4 Utilities folder. Double-click icon
to launch the app. Or, simply drag the movie le onto the Mbox File Convertor icon. If les are dropped
directly onto the application’s icon, then they will be processed with the most recently used settings (if
applicable).
Step 2. If the application is launched rst, the conversion settings can be adjusted. Adjust as required. Refer to
“File Conversion Settings” on the previous page.
Step 3. Once the settings are adjusted, drag and drop one or more movie les onto the application window.
Step 4. After conversion, manually remove the original les from the folder, so there are not two les with the same
index value.
CAUTION! Movie le conversion to the ProRes and Hap codecs requires that those codecs to be installed on the
computer, otherwise the conversion will fail. The current version of the Mbox File Convertor application (v4.1) continues
to rely on QuickTime technology to convert movies. It may not work on computers with newer operating systems
beyond El Capitan/Sierra.