NSNumber object containing the duration (in seconds) of the current frame for an animated GIF image.
The frame duration can be a floating-point value. It is used when reading in, but not when writing out.
static let fallbackBackgroundColor: NSBitmapImageRep.PropertyKey
Specifies the background color to use when writing to an image format (such as JPEG) that doesn't support alpha. The color's alpha value is ignored. The default background color, when this property is not specified, is white. The value of the property should be an
NSColor object. This constant corresponds to the kCGImageDestinationBackgroundColor constant in Quartz.