Kdenlive/Manual/Effects/Alpha manipulation: Difference between revisions

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==== General Information about Alpha Manipulation  ==== <!--T:25-->  
==== General Information about Alpha Manipulation  ==== <!--T:25-->  


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Alpha Manipulation, more commonly known as Chroma Key compositing is an effect that changes the background of the picture to a different background the editor may want.
In previous versions of Kdenlive (<17.04 ??) Alpha Manipulation effects  always needed to be used in combination with a [[Special:myLanguage/Kdenlive/Manual/Transitions/Composite|composite transition]] or an [[Special:myLanguage/Kdenlive/Manual/Transitions/Affine|Affine transition]] . This is because Alpha Manipulation has to do with manipulating the so called "alpha-channel" of images and videos. The alpha channel is data that describes how two images are to be combined (or composited) into one. So you needed a composite (or affine) transition on the timeline to tell '''Kdenlive''' that you are compositing the videos from two different tracks into one image.  


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More information can be found on the pages for the effects themselves:
However, in version 17.04 of kdenlive an option was introduced that automatically composited two tracks that have Alpha channel data in them.  You turn this feature on by selecting either [[Special:myLanguage/Kdenlive/Manual/Timeline/Editing#Track_Compositing_-_HighQuality|High Quality]] or or [[Special:myLanguage/Kdenlive/Manual/Timeline/Editing#Track_Compositing_-_Preview|Preview]] from the Compositing Option drop down found under the Project Bin. Select None from this drop down to turn this feature off.
 
{|
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| [[File:Two tracks no transition.png|left]] || This image shows two video tracks with no transition.<br />The project monitor shows how the upper track takes precedence when no transition is in play.
# [[Special:myLanguage/Kdenlive/Manual/Effects/Alpha manipulation/Blue Screen|Chroma Key ]] (for simple chroma key effects)</translate>
|}
<translate>
<br/>
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# [[Special:myLanguage/Kdenlive/Manual/Effects/Alpha manipulation/Color Selection|Color Selection]] (for complex chroma key effects)</translate>
<translate>


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{|
| [[File:Two tracks composite transition no alpha info.png|400px|left]] || This image shows two video tracks with a composite transition in place but with no alpha information to tell '''Kdenlive''' how to combine the images.<br />With a composite transition but no alpha info to describe how to composite the picture, the top track still takes precedence.
|}


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{|
| [[File:Two tracks composite transition with alpha info.png|400px|left]] || This image shows the situation with alpha info now added via the blue screen method.<br />The blue screen effect is also known as "Color to alpha" [http://www.mltframework.org/bin/view/MLT/FilterFrei0r-bluescreen0r] and all the blue screen effect does is say that where the video is blue, the alpha value is 0 (i.e. transparent).<br />So now that we have alpha information, the second track's image shows through where the alpha channel says the image should be transparent.
|}


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# [[Special:myLanguage/Kdenlive/Manual/Effects/Alpha manipulation/Rotoscoping|Rotoscoping]]
Once you have some alpha channel data in play you can alter the settings in your [[Special:myLanguage/Kdenlive/Manual/Transitions/Composite|composite transition]] to change how the images will combine. See the [[Special:myLanguage/Kdenlive/Manual/Transitions/Composite|composite transition]] page for details.
# [[Special:myLanguage/Kdenlive/Manual/Effects/Misc/keysplillm0pup|Key Spill Mop Up]]


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You can also combine two video tracks together using the [[Special:myLanguage/Kdenlive/Manual/Transitions/screen|screen]] transition (if one of them is filmed on a black background).


==== Hint for previewing the alpha manipulation effects ==== <!--T:9-->
==== Hint for previewing the alpha manipulation effects ==== <!--T:9-->
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==== Effects in the Alpha Manipulation Category ==== <!--T:13-->
==== Effects in the Alpha Manipulation Category ====  
 
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# [[Special:myLanguage/Kdenlive/Manual/Effects/Alpha manipulation/Alpha gradient|Alpha gradient]]</translate>
# [[Special:myLanguage/Kdenlive/Manual/Effects/Alpha manipulation/Alpha gradient|Alpha gradient]]</translate>
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<translate>
<translate>
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# [[Special:myLanguage/Kdenlive/Manual/Effects/Alpha manipulation/Blue Screen|Chroma Key ]] (formerly Blue Screen)</translate>
# [[Special:myLanguage/Kdenlive/Manual/Effects/Alpha manipulation/Blue Screen|Chroma Key ]] (for simple chroma key effects)</translate>
<translate>
<translate>
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# [[Special:myLanguage/Kdenlive/Manual/Effects/Alpha manipulation/Color Selection|Color Selection]]</translate>
# [[Special:myLanguage/Kdenlive/Manual/Effects/Alpha manipulation/Color Selection|Color Selection]] (for complex chroma key effects)</translate>
<translate>
<translate>
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# [[Special:myLanguage/Kdenlive/Manual/Effects/Alpha manipulation/Mask0Mate|Rectangular Alpha mask]]  (Formerly Mask0Mate)</translate>
# [[Special:myLanguage/Kdenlive/Manual/Effects/Alpha manipulation/Mask0Mate|Rectangular Alpha mask]]  (Formerly Mask0Mate)</translate>
<translate>
<translate>
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# [[Special:myLanguage/Kdenlive/Manual/Effects/Alpha manipulation/Rotoscoping|Rotoscoping]]
# [[Special:myLanguage/Kdenlive/Manual/Effects/Misc/keysplillm0pup|Key Spill Mop Up]]


==== Compositing Reference Material ==== <!--T:15-->
==== Compositing Reference Material ==== <!--T:15-->

Revision as of 13:00, 31 March 2019

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Effects - Alpha manipulation

General Information about Alpha Manipulation

Alpha Manipulation, more commonly known as Chroma Key compositing is an effect that changes the background of the picture to a different background the editor may want.

More information can be found on the pages for the effects themselves:

  1. Chroma Key (for simple chroma key effects)
  2. Color Selection (for complex chroma key effects)


  1. Rotoscoping
  2. Key Spill Mop Up


Hint for previewing the alpha manipulation effects

The preview in Project monitor might go all strange when you select the composite transition in the timeline or the Video 1 in the timeline. (Reported at bug 2990 and fixed in ver >=0.9.5 of Kdenlive)

This is what the project monitor looks like when you have just selected the composite transition in the timeline. This is not what the rendered video will look like. To get a preview of what the rendered video will look like, you need to click Video 1 and then Video 2 in the timeline.

What the preview looks like once you select Video 2 in the timeline. This is what the rendered file will look like



Effects in the Alpha Manipulation Category

  1. Alpha gradient
  2. Alpha operations
  3. Alpha shapes
  4. Chroma Key (for simple chroma key effects)
  5. Color Selection (for complex chroma key effects)
  6. Rectangular Alpha mask (Formerly Mask0Mate)

Compositing Reference Material

For some background, the Wikipedia article in alpha compositing is useful. See also Porter, Thomas; Tom Duff (1984). "Compositing Digital Images". Computer Graphics 18 (3): p253–259 1984 pdf

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