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70 lines
2.2 KiB
Plaintext
70 lines
2.2 KiB
Plaintext
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Veejay has some support for alpha channel compositing
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In general, you will need to add an alpha channel to your playing sample or stream by using one of the "Alpha:" filters in veejay
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Then, the alpha channel will be combined by FX that can deal with Alpha. Some of such effects have a mode parameter "Alpha" that functions like an on/off switch but others require an alpha channel to work.
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By default, the alpha channel is set to 0 (completely invisible) so such effects will always result in a black screen if you have not added an alpha channel
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The 'Select by Color Key' operator
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-----------------------------------
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Use this filter to create an alpha channel from the foreground object.
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The filter requires an existing alpha channel to decide which pixel from source B to composite in. Pixels with an alpha of 0 are skipped.
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Using the parameters R,G,B and Angle you can select which pixels belong to the background and key them out, leaving a mask of the foreground object.
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Luma Key
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--------
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Luma Key in Mode 3 will not composite-in pixels from source B if its alpha channel value is 0
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Black and White Mask by Threshold
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---------------------------------
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This filter creates a black/white image from a minimum and maximum threshold value. You can set a mode parameter so that the render result is written as an Alpha channel
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LVD Scale0Tilt / Crop,Scale,Tilt
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---------------------------------
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This filter is a port of the frei0r filter "scale0tilt.so"
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You can use it to crop,scale, tilt an image from source B over source A
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If the Alpha paramater is set to 1, the final result will be an opaque pixel with the transparency of each pixel determined by the alpha channel values
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Flatten Image
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-------------
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Use this to multiply the alpha channel against a black background
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Alpha Fill
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----------
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Solid value fill of the alpha channel, 0 - 255
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Set from Image / Mixing source
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------------------------------
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Use the luminance channel of the image as a new Alpha channel
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You can use the FX switch parameter to scale the values to full range (0-255) if needed.
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If you have no result in the Alpha channel, flip this parameter.
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Alpha to Greyscale
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-------------------
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Use this FX to display the alpha channel as a greyscale image.
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