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veejay/veejay-current/veejay-server/doc/README.alpha
2015-11-30 00:02:47 +01:00

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\ \ __ \ \ \ \____ \ \ _-/ \ \ __ \ \ \ __ \
\ \_\ \_\ \ \_____\ \ \_\ \ \_\ \_\ \ \_\ \_\
\/_/\/_/ \/_____/ \/_/ \/_/\/_/ \/_/\/_/
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/\ ___\ /\ \_\ \ /\ __ \ /\ "-.\ \ /\ "-.\ \ /\ ___\ /\ \
\ \ \____ \ \ __ \ \ \ __ \ \ \ \-. \ \ \ \-. \ \ \ __\ \ \ \____
\ \_____\ \ \_\ \_\ \ \_\ \_\ \ \_\\"\_\ \ \_\\"\_\ \ \_____\ \ \_____\
\/_____/ \/_/\/_/ \/_/\/_/ \/_/ \/_/ \/_/ \/_/ \/_____/ \/_____/
in veejay
Veejay has some support for alpha channel compositing
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
Then, the alpha channel will be combined used FX that can deal with Alpha. Some effects have a mode parameter "Alpha" that functions like an on/off switch but others require an alpha channel to work.
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.
In Reloaded, you can toggle the white button next to 'Alpha Clear' to switch between 0 (completely invisible) and 255 (completely visible)
Also, you can toggle the alpha-button to set the fade method to alpha blending in the (manual) chain fader
The chain fader fades the original (unchanged) image to the image that is rendered by the FX chain, either with an opacity value or by using alpha channel information
The chain fader is located next to the FX chain (the vertical slider).
Everything related to alpha compositing is in development and feedback is ofcourse welcome
List of Alpha: FX
==================
The 'Set by Color Key' operator
-----------------------------------
Use this filter to create an alpha channel from the foreground object.
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.
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.
The 'Select by Chroma Key' operator
-----------------------------------
Use this filter to create an alpha channel from the foreground object.
The filter may use an existing alpha channel to decide which pixel from source B to composite in. Pixels with an alpha of 0 are skipped optionally.
Luma Key
--------
Luma Key in Mode 3 will composite-in pixels from source B using its alpha channel
Alpha Blend
------------
Image in source B will be blended on top of source A using its alpha channel
Black and White Mask by Threshold
---------------------------------
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
LVD Scale0Tilt / Crop,Scale,Tilt
---------------------------------
This filter is a port of the frei0r filter "scale0tilt.so"
You can use it to crop,scale, tilt an image from source B over source A
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
Flatten Image
-------------
Use this to multiply the alpha channel against a black background
Alpha Fill
----------
Solid value fill of the alpha channel, 0 - 255
Set from Image / Mixing source
------------------------------
Use the luminance channel of the image as a new Alpha channel
You can use the FX switch parameter to scale the values to full range (0-255) if needed.
If you have no result in the Alpha channel, flip this parameter.
Alpha to Greyscale
-------------------
Use this FX to display the alpha channel as a greyscale image.
Transition Map
--------------
Use this FX to blend over time using a greyscale image as an opacity map