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98 lines
3.9 KiB
Markdown
98 lines
3.9 KiB
Markdown
```
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______ __ ______ __ __ ______
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/\ __ \ /\ \ /\ == \ /\ \_\ \ /\ __ \
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\ \ __ \ \ \ \____ \ \ _-/ \ \ __ \ \ \ __ \
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\ \_\ \_\ \ \_____\ \ \_\ \ \_\ \_\ \ \_\ \_\
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\/_/\/_/ \/_____/ \/_/ \/_/\/_/ \/_/\/_/
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______ __ __ ______ __ __ __ __ ______ __
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/\ ___\ /\ \_\ \ /\ __ \ /\ "-.\ \ /\ "-.\ \ /\ ___\ /\ \
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\ \ \____ \ \ __ \ \ \ __ \ \ \ \-. \ \ \ \-. \ \ \ __\ \ \ \____
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\ \_____\ \ \_\ \_\ \ \_\ \_\ \ \_\\"\_\ \ \_\\"\_\ \ \_____\ \ \_____\
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\/_____/ \/_/\/_/ \/_/\/_/ \/_/ \/_/ \/_/ \/_/ \/_____/ \/_____/
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in veejay
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```
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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
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stream by using one of the "Alpha:" filters in veejay.
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Then, the alpha channel will be combined used FX that can deal with Alpha. Some
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effects have a mode parameter `Alpha` that functions like an on/off switch but
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others require an extra alpha channel to work.
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By default, the alpha channel is set to `0` (completely invisible) so such effects
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will always result in a black screen if you have not added an alpha channel.
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In Reloaded, you can toggle the white button next to 'Alpha Clear' to switch
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between `0` (completely invisible) and `255` (completely visible)
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Also, you can toggle the alpha-button to set the fade method to alpha blending
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in the (manual) chain fader
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The chain fader fades the original (unchanged) image to the image that is rendered
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by the FX chain, either with an opacity value or by using alpha channel information
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In Reloaded, the chain fader is located next to the FX chain (the vertical slider).
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_Alpha compositing is still in development and feedback is of course welcome_
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List of "Alpha:" FX
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-------------------
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* **The 'Set by Color Key' operator**
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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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* **The 'Select by Chroma Key' operator**
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Use this filter to create an alpha channel from the foreground object.
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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.
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* **Luma Key**
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Luma Key in `Mode 3` will composite-in pixels from source B using its alpha channel
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* **Alpha Blend**
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Image in source B will be blended on top of source A using its alpha channel
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* **Black and White Mask by Threshold**
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This filter creates a black/white image from a minimum and maximum threshold value.
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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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This filter is a port of the [frei0r](https://frei0r.dyne.org/) 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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Use this to multiply the alpha channel against a black background
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* **Alpha Fill**
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Solid value fill of the alpha channel into `0 - 255` range
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* **Set from Image / Mixing source**
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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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Use this FX to display the alpha channel as a greyscale image.
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* **Transition Map**
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Use this FX to blend over time using a greyscale image as an opacity map
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