Convert the layer image format.
This method converts the image representation between "types with different image representations of layers but capable of similar representation", such as ltAlpha (dfAlpha) and ltAddAlpha (dfAddAlpha).
For example, simply changing the type of the layer displayed by ltAlpha to ltAddAlpha as it is will not be displayed correctly because the handling of the alpha channel and color information will be different. Therefore, you need to use this method to convert from dfAlpha to dfAddAlpha.
In this method, the image representation format of the conversion destination will be the format corresponding to the drawing method specified by the Layer.face property (note that it is not the layer type specified by Layer.type, but the drawing method).
For the from argument, specify the drawing method (constants starting with df; see Layer.face) corresponding to the image representation format of the conversion source. dfAuto cannot be specified in the from argument.
Currently supported conversions are dfAlpha → dfAddAlpha and dfAddAlpha → dfAlpha. In dfAddAlpha → dfAlpha, color information may be lost due to conversion.
This method is not affected by the drawing clip rectangle (always the entire layer image).