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

Revision as of 20:40, 31 March 2019

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:

Chroma Key (formerly Blue Screen)
Color Selection

Alpha gradient
Alpha operations
Alpha shapes
[[Special:myLanguage/Kdenlive/Manual/Effects/Alpha manipulation/Blue Screen|Chroma Key ]
Color Selection
Rectangular Alpha mask (Formerly Mask0Mate)
Rotoscoping
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

@@ Line 5: / Line 5: @@
 ==== General Information about Alpha Manipulation  ====
-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.
+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.
-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.
+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.
-|}
-<br/>
-{|
+# [[Special:myLanguage/Kdenlive/Manual/Effects/Alpha manipulation/Blue Screen|Chroma Key ]] (formerly Blue Screen)
-| [[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.
+# [[Special:myLanguage/Kdenlive/Manual/Effects/Alpha manipulation/Color Selection|Color Selection]]
-|}
-{|
-| [[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.
-|}
-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.
-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 timeline or the Video 1 in the timeline.  (Reported at bug [http://www.kdenlive.org/mantis/view.php?id=2990 2990] and fixed in ver >=0.9.5 of Kdenlive)
-[[File:Weird preview look.png|400px|left]]
-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.
-<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 ====
 # [[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 shapes|Alpha shapes]]
-# [[Special:myLanguage/Kdenlive/Manual/Effects/Alpha manipulation/Blue Screen|Chroma Key ]] (formerly 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/Mask0Mate|Rectangular Alpha mask]]  (Formerly Mask0Mate)
 # [[Special:myLanguage/Kdenlive/Manual/Effects/Alpha manipulation/Rotoscoping|Rotoscoping]]
 # [[Special:myLanguage/Kdenlive/Manual/Effects/Misc/keysplillm0pup|Key Spill Mop Up]]
 ==== Compositing Reference Material ====