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=== Effects - Alpha manipulation ===
=== Alpha manipulation ===


==== General Information about Alpha Manipulation  ====
==== General Information about Alpha Manipulation  ====  


As far as I am aware Alpha Manipulation effects are always used in combination with a [[Special:myLanguage/Kdenlive/Manual/Transitions/Composite|composite transition]]. This because Alpha Manipulation is 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 need a composite transition on the timeline to tell '''Kdenlive''' that you are compositing the videos from two different tracks into one image.  
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:
| [[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)
| [[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 composite transition but no alpha info to describe how to composite the picture the top track still takes precedence.
# [[Special:myLanguage/Kdenlive/Manual/Effects/Alpha manipulation/Color Selection|Color Selection]] (for complex chroma key effects)
|}


{|
| [[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 tracks image now shows through where the alpha channel says the image should be transparent.
|}


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 [[Special:myLanguage/Kdenlive/Manual/Transitions/Composite|composite transition]] page for details.


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 ====
The preview in Project monitor might go all strange when you select the composite transition in the time line or the video 1 in the time line.  (Reported at bug [http://www.kdenlive.org/mantis/view.php?id=2990 2990])
[[File:Weird preview look.png|400px|left]]
What the project monitor looks like when you have just selected the composite transition in the time line. This is not what the rendered video will look like.
To get a look at what the video will render as you need to click Video 1 and then Video 2 in the timeline.
<br style="clear: both;"/>
[[File:Two tracks composite transition with alpha info.png|400px|left]] What the preview looks like once you select Video 2 in the timeline. This is what the rendered file will look like
<br style="clear: both;"/>
<br />


==== Effects in the Alpha Manipulation Category ====
==== Effects in the Alpha Manipulation Category ====
# [[Special:myLanguage/Kdenlive/Manual/Effects/Alpha manipulation/Alpha gradient|Alpha gradient]]
# [[Special:myLanguage/Kdenlive/Manual/Effects/Alpha manipulation/Alpha gradient|Alpha gradient]]
# [[Special:myLanguage/Kdenlive/Manual/Effects/Alpha manipulation/Alpha operations|Alpha operations]]
# [[Special:myLanguage/Kdenlive/Manual/Effects/Alpha manipulation/Alpha operations|Alpha operations]]
# [[Special:myLanguage/Kdenlive/Manual/Effects/Alpha manipulation/Alpha shapes|Alpha shapes]]
# [[Special:myLanguage/Kdenlive/Manual/Effects/Alpha manipulation/Alpha shapes|Alpha shapes]]
# [[Special:myLanguage/Kdenlive/Manual/Effects/Alpha manipulation/Blue Screen|Blue Screen]]
# [[Special:myLanguage/Kdenlive/Manual/Effects/Alpha manipulation/Blue Screen|Chroma Key ]]
# [[Special:myLanguage/Kdenlive/Manual/Effects/Alpha manipulation/Color Selection|Color Selection]]
# [[Special:myLanguage/Kdenlive/Manual/Effects/Alpha manipulation/Color Selection|Color Selection]]  
# [[Special:myLanguage/Kdenlive/Manual/Effects/Alpha manipulation/Mask0Mate|Mask0Mate]]
# [[Special:myLanguage/Kdenlive/Manual/Effects/Alpha manipulation/Mask0Mate|Rectangular Alpha mask]]  
# [[Special:myLanguage/Kdenlive/Manual/Effects/Alpha manipulation/Rotoscoping|Rotoscoping]]
# [[Special:myLanguage/Kdenlive/Manual/Effects/Alpha manipulation/Rotoscoping|Rotoscoping]]
# [[Special:myLanguage/Kdenlive/Manual/Effects/Misc/keysplillm0pup|keysplillm0pup]]
# [[Special:myLanguage/Kdenlive/Manual/Effects/Misc/keysplillm0pup|Key Spill Mop Up]]


==== Compositing Reference Material ====
==== Compositing Reference Material ====


For some background the Wikipedia article in [http://en.wikipedia.org/wiki/Alpha_compositing alpha compositing] is usefull. See also Porter, Thomas; Tom Duff (1984). "Compositing Digital Images". Computer Graphics 18 (3): p253–259 1984 [http://keithp.com/~keithp/porterduff/p253-porter.pdf pdf]
For some background, the Wikipedia article in [http://en.wikipedia.org/wiki/Alpha_compositing alpha compositing] is useful. See also Porter, Thomas; Tom Duff (1984). "Compositing Digital Images". Computer Graphics 18 (3): p253–259 1984 [http://keithp.com/~keithp/porterduff/p253-porter.pdf pdf]


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[[Category:Kdenlive]]
[[Category:Kdenlive]]

Latest revision as of 12:59, 15 August 2023

Other languages:

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)



Effects in the Alpha Manipulation Category

  1. Alpha gradient
  2. Alpha operations
  3. Alpha shapes
  4. Chroma Key
  5. Color Selection
  6. Rectangular Alpha mask
  7. Rotoscoping
  8. Key Spill Mop Up

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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