# alpha

The alpha element adds an alpha channel to a video stream. The values of the alpha channel can be either be set to a constant or can be dynamically calculated via chroma keying, e.g. blue can be set as the transparent color.

Sample pipeline:

     gst-launch-1.0 videotestsrc pattern=snow ! mixer.sink_0 \
       videotestsrc pattern=smpte75 ! alpha method=green ! mixer.sink_1 \
       videomixer name=mixer sink_0::zorder=0 sink_1::zorder=1 ! \
       videoconvert ! autovideosink

This pipeline adds a alpha channel to the SMPTE color bars with green as the transparent color and overlays the output on top of a snow video stream.

## Hierarchy

    GObject
        ╰──GInitiallyUnowned
            ╰──GstObject
                ╰──GstElement
                    ╰──GstBaseTransform
                        ╰──GstVideoFilter
                            ╰──alpha

## Factory details

Authors: – Wim Taymans , Edward Hervey , Jan Schmidt

Classification: – `Filter/Effect/Video`

Rank – none

Plugin – alpha

Package – GStreamer Good Plug-ins

## Pad Templates

### `sink`

    video/x-raw:
             format: { AYUV, ARGB, BGRA, ABGR, RGBA, Y444, xRGB, BGRx, xBGR, RGBx, RGB, BGR, Y42B, YUY2, YVYU, UYVY, I420, YV12, Y41B }
              width: [ 1, 2147483647 ]
             height: [ 1, 2147483647 ]
          framerate: [ 0/1, 2147483647/1 ]

Presence – always

Direction – sink

Object type – GstPad

### `src`

    video/x-raw:
             format: { AYUV, ARGB, BGRA, ABGR, RGBA, Y444, xRGB, BGRx, xBGR, RGBx, RGB, BGR, Y42B, YUY2, YVYU, UYVY, I420, YV12, Y41B }
              width: [ 1, 2147483647 ]
             height: [ 1, 2147483647 ]
          framerate: [ 0/1, 2147483647/1 ]

Presence – always

Direction – src

Object type – GstPad

## Properties

### alpha

    “alpha” gdouble

The value for the alpha channel

Flags : Read / Write

Default value : 1

### angle

    “angle” gfloat

Size of the colorcube to change

Flags : Read / Write

Default value : 20

### black-sensitivity

    “black-sensitivity” guint

Sensitivity to dark colors

Flags : Read / Write

Default value : 100

### method

    “method” GstAlphaMethod *

How the alpha channels should be created

Flags : Read / Write

Default value : set (0)

### noise-level

    “noise-level” gfloat

Size of noise radius

Flags : Read / Write

Default value : 2

### prefer-passthrough

    “prefer-passthrough” gboolean

Don't do any processing for alpha=1.0 if possible

Flags : Read / Write

Default value : false

### target-b

    “target-b” guint

The blue color value for custom RGB chroma keying

Flags : Read / Write

Default value : 0

### target-g

    “target-g” guint

The green color value for custom RGB chroma keying

Flags : Read / Write

Default value : 255

### target-r

    “target-r” guint

The red color value for custom RGB chroma keying

Flags : Read / Write

Default value : 0

### white-sensitivity

    “white-sensitivity” guint

Sensitivity to bright colors

Flags : Read / Write

Default value : 100

## Named constants

### GstAlphaMethod

#### Members

`set` (0) – Set/adjust alpha channel
`green` (1) – Chroma Key on pure green
`blue` (2) – Chroma Key on pure blue
`custom` (3) – Chroma Key on custom RGB values

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