This lesson is accompanied by photocopies from a textbook and a product manual. If you don't have those photocopies, see Dr. Moshell. This online document contains queries based on those handouts.
Query 26.2: When we're storing an image with transparency, we prefer to store not R G B and alpha (call it a) like (R G B a), but (R*a G*a B*a a). Why do we do that?
The former is called straight alpha and the latter is called pre-multiplied alpha.
Query 26.3: Use the terminology introduced in the handout's Figure 17.7 to describe the following scene:
A cloud passes over the sun, which is shining in the midst of a blue sky. On the horizon are mountains, and a pine tree stands in the foreground. You can see the clouds, sun, sky and mountains through the tree's branches. A house has a window-shaped hole cut it in, through which you can see the mountains.
Your objects: sun, cloud, sky, mountain, tree, house, window. The tree and cloud are partially transparent.
Query 26.4: Explain the visual difference between a progressive darken operation and a progressive fade operation. Illustrate with an example of a bright red foreground object.
Adobe Premier is an accessible (i. e., affordable) package that runs on Wintel and Macintosh computers. The features it supports include:
assembly editing
transitions
motion
transparency
titling
sound synchronization
Rough Cut: just assemble the pieces in order, no transitions. For quick look-see. Set in points and out points. This way you don't have to discard the beginnings and endings of your clips, as you may later want to move an in point back or an out point forward.
Moving a pair of clips backward and forward across the transition is called scrubbing it, and is done by a slider control.
You can change a clip's speed - (but how? Where do the new frames come from?)
You can vary the opacity of a manipulate filters such as a blur using keyframes.
You can specify a key color and associate it with a particular clip, in which the named color becomes transparent. This is sometimes called chroma keying.
You can animate one clip's position, orientation and scale with respect to the frame (or anything else underneath or above it.)
Transitions - there are 75 different kinds of transitions available in Premier! Image Mask transitions, for instance, allow you to select an image file. The white portions of the image mask cause data to be selected from one clip, and the black portions receive data from the other clip.
You can even specify custom transitions by using arithm,etic expressions to describe how alpha, r g and b are to be affected. The tool is called the Transition Factory.
Projects are used (just like in Visual Studio) to keep all the clips, sounds and timing information (in an edit decision list, or EDL file) for a movie in one place. You render the final movie into a single coherent file, but you can also keep all the pieces for subsequent editing. You can render into Quicktime, MPEG, .MOV
You can use an EDL that is originally made on a low cost (PC) system, with low resolution clips, to control a high priced system with broadcast quality clips. Ergo, time and money saving.
Time and Frames
What do we do about the fact that film is shot at 24 frames a second and video is 30 frames/sec (actually 29.97)? For that matter, how do we show a movie on TV? Well, you just have to show some film frames more than once. The human eye, it turns out, doesn't notice the small duplication, because the rate of change in the scene remains constant.
Capturing Analog information
You have a VCR tape; how do you get it into Premier? Gotta buy a video capture board, or borrow one.
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