AlphaChannelType

Enable the image's transparency channel. Note normally SetAlphaChannel should be used instead of this, unless you specifically need to preserve existing (but specifically turned Off) transparency channel.

Set any fully-transparent pixel to the background color, while leaving it fully-transparent. This can make some image file formats, such as PNG, smaller as the RGB values of transparent pixels are more uniform, and thus can compress better.

Turns On the alpha/matte channel, then copies the gray-scale intensity of the image, into the alpha channel, converting a gray-scale mask into a transparent shaped mask ready to be colored appropriately. The color channels are not modified.

Disables the image's transparency channel. Does not delete or change the existing data, just turns off the use of that data.

Copies the alpha channel values into all the color channels and turns 'Off' the the image's transparency, so as to generate a gray-scale mask of the image's shape. The alpha channel data is left intact just deactivated. This is the inverse of CopyAlphaChannel.

Enables the alpha/matte channel and forces it to be fully opaque.

Activates the alpha/matte channel. If it was previously turned off then it also resets the channel to opaque. If the image already had the alpha channel turned on, it will have no effect.

As per CopyAlphaChannel but also colors the resulting shape mask with the current background color. That is the RGB color channels is replaced, with appropriate alpha shape.

Activates the alpha/matte channel and forces it to be fully transparent. This effectively creates a fully transparent image the same size as the original and with all its original RGB data still intact, but fully transparent.

Flatten image pixels over the background pixels.

Since: ImageMagick 6.7.6.

ditto