ImageGamma#

ImageGamma(value[, property_name])

gamma correction applied to the image

Graphic Feature value, must be implemented in subclass

`ImageGamma.add_event_handler`(handler)	Add an event handler.
`ImageGamma.block_events`(val)	Block all events from this feature
`ImageGamma.clear_event_handlers`()	Clear all event handlers
`ImageGamma.remove_event_handler`(handler)	Remove a registered event `handler`.
`ImageGamma.set_value`(graphic_or_key, value, ...)	wraps GraphicFeature.set_value