(PECL gmagick >= Unknown)
Gmagick::setimagetype — Sets the image type
imgTypeThe image type: UndefinedType, BilevelType, GrayscaleType, GrayscaleMatteType, PaletteType, PaletteMatteType, TrueColorType, TrueColorMatteType, ColorSeparationType, ColorSeparationMatteType, or OptimizeType.
The Gmagick object on success.
错误时抛出 GmagickException。