alpha

alpha — Adds an alpha channel to video - uniform or via chroma-keying

Synopsis

struct              GstAlpha;
enum                GstAlphaMethod;

Object Hierarchy

  GObject
   +----GInitiallyUnowned
         +----GstObject
               +----GstElement
                     +----GstBaseTransform
                           +----GstVideoFilter
                                 +----GstAlpha

Properties

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

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=smpte75 ! alpha method=green ! \
  videomixer name=mixer ! videoconvert ! autovideosink     \
  videotestsrc pattern=snow ! mixer.

This pipeline adds a alpha channel to the SMPTE color bars with green as the transparent color and mixes the output with 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 ]

Details

struct GstAlpha

struct GstAlpha;


enum GstAlphaMethod

typedef enum {
  ALPHA_METHOD_SET,
  ALPHA_METHOD_GREEN,
  ALPHA_METHOD_BLUE,
  ALPHA_METHOD_CUSTOM,
} GstAlphaMethod;

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               : Read / Write

The value for the alpha channel.

Allowed values: [0,1]

Default value: 1


The "angle" property

  "angle"                    gfloat                : Read / Write

Size of the colorcube to change.

Allowed values: [0,90]

Default value: 20


The "method" property

  "method"                   GstAlphaMethod        : Read / Write

How the alpha channels should be created.

Default value: Set/adjust alpha channel


The "noise-level" property

  "noise-level"              gfloat                : Read / Write

Size of noise radius.

Allowed values: [0,64]

Default value: 2


The "target-b" property

  "target-b"                 guint                 : Read / Write

The blue color value for custom RGB chroma keying.

Allowed values: <= 255

Default value: 0


The "target-g" property

  "target-g"                 guint                 : Read / Write

The green color value for custom RGB chroma keying.

Allowed values: <= 255

Default value: 255


The "target-r" property

  "target-r"                 guint                 : Read / Write

The red color value for custom RGB chroma keying.

Allowed values: <= 255

Default value: 0


The "black-sensitivity" property

  "black-sensitivity"        guint                 : Read / Write

Sensitivity to dark colors.

Allowed values: <= 128

Default value: 100


The "white-sensitivity" property

  "white-sensitivity"        guint                 : Read / Write

Sensitivity to bright colors.

Allowed values: <= 128

Default value: 100


The "prefer-passthrough" property

  "prefer-passthrough"       gboolean              : Read / Write

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

Default value: FALSE