Archive:Kdenlive/Manual/Effects/Alpha manipulation/Alpha operations

Alpha operations

This is Frei0r alpha0ps - Display and manipulation of the alpha channel

Use this to shrink, grow, threshold and visualize the alpha channel.

From the Frei0r-alpha0p readme file:

This plugin can shrink, grow, threshold and invert the alpha channel. It is mainly intended to improve keying edges. It can also display the alpha channel in various ways, to enable quick assessment of the effect. It is cascadable, so for example one can do a soft shrink first and then threshold, which gives a slightly different result than a hard shrink.

Parameters:

Display:
what to display. Choices are seven: Image, Alpha as gray, Gray+red, Selection on black, Selection on gray, Selection on white and Selection on checkers.

This is intended for monitoring during adjustment mostly. After adjusting the parameters, it should be left on "Image", which lets the unchanged input image through - this plugin is intended to change only the alpha channel...

Display input alpha:
use input alpha for the display function above. (Check what alpha we are getting on the input)

'Operation:
select the operation to be done on the alpha channel. Currently there are six choices: NO OP, Shave, Shrink hard, Shrink soft, Grow hard, Grow soft, Threshold.

"Shave" try to remove the "hairy" stuff, and also shrinks the selecton a bit.

The "hard" operations introduce no new values to the alpha channel, so if you have a "hard" key (only 0 and 255) it will stay that way. The "soft" operations will introduce interpolated values, making the edge softer. NOTE: the shave, shrink and grow operations are quite slow, because they do many conditional operations on each pixel.

Threshold:
this is only used for the Threshold operation.

Shrink/grow amount:
how far the shrinking/growing will extend.

Invert:
Inverts the input alpha channel, transparent will become opaque and vice versa.

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Display Menu Options

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Operation Menu Options

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Tutorial 1

See this tutorial that describes how to use

• Alpha Manipution>Blue Screen
• rotoscoping
• Composite Transition
• Crop and Transform>Pan and Zoom effect
• Enhancment>Sharpen Effect
• Alpha Manipution>Alpha Operations

Tutorial 2

Shows usage of alpha operations - shrinkhard as well as the following effects: blue screen, denoiser and keysplillm0pup {{#ev:youtube|l43Hz7YEcYU}}