alpha: GStreamer Good Plugins 1.0 Plugins Reference Manual

## alpha alpha |

## Properties

gdouble | alpha | Read / Write
gfloat | angle | Read / Write
GstAlphaMethod | method | Read / Write
gfloat | noise-level | Read / Write
guint | target-b | Read / Write
guint | target-g | Read / Write
guint | target-r | Read / Write
guint | black-sensitivity | Read / Write
guint | white-sensitivity | Read / Write
gboolean | prefer-passthrough | Read / Write

## Types and Values

struct | GstAlpha
enum | GstAlphaMethod

## Object Hierarchy

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

## Description

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:

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    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.

## Synopsis

### Element Information

plugin | alpha
author | Wim Taymans <wim.taymans@gmail.com> Edward Hervey <edward.hervey@collabora.co.uk> Jan Schmidt <thaytan@noraisin.net>
class | Filter/Effect/Video

### Element Pads

name | sink
direction | sink
presence | always
details | video/x-raw, format=(string){ AYUV, ARGB, BGRA, ABGR, RGBA, Y444, xRGB, BGRx, xBGR, RGBx, RGB, BGR, Y42B, YUY2, YVYU, UYVY, I420, YV12, Y41B }, width=(int)[ 1, 2147483647 ], height=(int)[ 1, 2147483647 ], framerate=(fraction)[ 0/1, 2147483647/1 ]

name | src
direction | source
presence | always
details | video/x-raw, format=(string){ AYUV, ARGB, BGRA, ABGR, RGBA, Y444, xRGB, BGRx, xBGR, RGBx, RGB, BGR, Y42B, YUY2, YVYU, UYVY, I420, YV12, Y41B }, width=(int)[ 1, 2147483647 ], height=(int)[ 1, 2147483647 ], framerate=(fraction)[ 0/1, 2147483647/1 ]

## Functions

## Types and Values

### struct GstAlpha

    struct GstAlpha;

### enum GstAlphaMethod

#### Members

ALPHA_METHOD_SET | Set/adjust alpha channel |
ALPHA_METHOD_GREEN | Chroma Key green |
ALPHA_METHOD_BLUE | Chroma Key blue |
ALPHA_METHOD_CUSTOM | Chroma Key on target_r/g/b |

## Property Details

### The `“alpha”` property

      “alpha”                    gdouble

The value for the alpha channel.

Flags: Read / Write

Allowed values: [0,1]

Default value: 1

### The `“angle”` property

      “angle”                    gfloat

Size of the colorcube to change.

Flags: Read / Write

Allowed values: [0,90]

Default value: 20

### The `“method”` property

      “method”                   GstAlphaMethod

How the alpha channels should be created.

Flags: Read / Write

Default value: Set/adjust alpha channel

### The `“noise-level”` property

      “noise-level”              gfloat

Size of noise radius.

Flags: Read / Write

Allowed values: [0,64]

Default value: 2

### The `“target-b”` property

      “target-b”                 guint

The blue color value for custom RGB chroma keying.

Flags: Read / Write

Allowed values: <= 255

Default value: 0

### The `“target-g”` property

      “target-g”                 guint

The green color value for custom RGB chroma keying.

Flags: Read / Write

Allowed values: <= 255

Default value: 255

### The `“target-r”` property

      “target-r”                 guint

The red color value for custom RGB chroma keying.

Flags: Read / Write

Allowed values: <= 255

Default value: 0

### The `“black-sensitivity”` property

      “black-sensitivity”        guint

Sensitivity to dark colors.

Flags: Read / Write

Allowed values: <= 128

Default value: 100

### The `“white-sensitivity”` property

      “white-sensitivity”        guint

Sensitivity to bright colors.

Flags: Read / Write

Allowed values: <= 128

Default value: 100

### The `“prefer-passthrough”` property

      “prefer-passthrough”       gboolean

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

Flags: Read / Write

Default value: FALSE