alpha channel

[Donna Kuhn]

i just do not understand what an alpha channel is. i have just discovered painting with my own msg effects, not just applying the effect but really painting with them and i was thrilled. still trying to grasp what all the different brushes do. i came across jean's tutorial regarding using multiple source images and was wondering if there was a way to do this with a canvas movie. i think i could do it with a movie stream but with a canvas movie it seemed i would have to keep unloading and loading the movie back in.

[beyond materials]

An alpha channel is a special kind of mask (like an acetate overlay) that allows you to control with great precision what shows through the channel (or overlay). For me, the easiest way to understand them is to look at alpha channels that got created for me in Photoshop, and try adding different levels of gray to the channel and see what it does to your image.

One common application of alpha channels is if you are blending two source images and using the alpha channel to selectively let some areas of one source image to mix into the composite image.

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[Synthetik]

You can associate different images or movies with the source or the canvas layers using the source or content keyframes in the layers window. so you could have a different source for each layer or you could have default content backgrounds for different layers. The content keyframes load into the layer whenever the timeline changes frame times, but you could then easily overwrite the image or movie frame by doing something in a paseq, so you need to be aware of what you are doing when using them.

the main canvas movie kind of sits on top of all the layers and you can move images back and forth to it from the layer stack. so you could be working with multiple source images and adding the results to a loaded canvas movie. but you can't really have multiple loaded canvas movies. you could kind of fake it out manually using content keyframes for the various movies, but you would have to hand load them when you changes layers.

the best way to think of alpha is to think of it as a mask that can have soft edges or transparency. it is typically used to define percent coverage for all the pixels in an object or layer. so if you wanted to add a soft edged circle you could paint a hard edged square with an alpha channel mask that defines the transparency at the soft edges of the circle.

[Donna Kuhn]

thank you for your reply. i think i will watch videos re. layers and keyframes so i can understand your answer! as far as the loaded canvas movie, i am usually handpainting a movie. when i add a source image the source movie goes away. i also wanted to check if i am correct in thinking that a movie stream records the actual process of painting but the loaded canvas movie shows just the final results of the process. also, when painting with msg effects do all the brushes besides the region fill and auto region use a paint synthesizer patch in addition to the effect?

[Synthetik]

A movie stream is basically an open quicktime file you created that you can stream frames to. IF you have the autowrite option turned on in movie stream preferences then yes it is a way to record the actual painting process.

The loaded canvas movie is an already existing quicktime movie that has been opened in the canvas that you can playback, single step through, and add or modify frames. So its a way to edit already existing quicktime files. And you can't record the actual painting process into it, you can just add or replace a frame.

If you are using a msg brush load paint preset, then the brush load image is created with the msg preset but everything else in the paint synth works the way it normally does, so all of the other paint synthesizer parameters are active and can be adjusted.