GdkPixbuf.Pixbuf.add_alpha

### Method

# GdkPixbuf Pixbufadd_alpha

#### Declaration [src]

    GdkPixbuf*
    gdk_pixbuf_add_alpha (
      const GdkPixbuf* pixbuf,
      gboolean substitute_color,
      guchar r,
      guchar g,
      guchar b
    )

#### Description [src]

Takes an existing pixbuf and adds an alpha channel to it.

If the existing pixbuf already had an alpha channel, the channel values are copied from the original; otherwise, the alpha channel is initialized to 255 (full opacity).

If `substitute_color` is `TRUE`, then the color specified by the (`r`, `g`, `b`) arguments will be assigned zero opacity. That is, if you pass `(255, 255, 255)` for the substitute color, all white pixels will become fully transparent.

If `substitute_color` is `FALSE`, then the (`r`, `g`, `b`) arguments will be ignored.

#### Parameters

`substitute_color`

  Type: `gboolean`

  Whether to set a color to zero opacity.

`r`

  Type: `guchar`

  Red value to substitute.

`g`

  Type: `guchar`

  Green value to substitute.

`b`

  Type: `guchar`

  Blue value to substitute.

#### Return value

Type: `GdkPixbuf`

A newly-created pixbuf.

The caller of the method takes ownership of the returned data, and is responsible for freeing it.
The return value can be `NULL`.