The alpha value ranges from 0.0 to 1.0 for each pixel.
If you use SetAlpha 0.5, then any alpha values in your image that are brighter than `half` will determine which pixels are masked in/out when using it for SetBlend MASKEDBLEND. Usually, pixels in your alpha channel will be either 1.0 or 0, where 1.0 means include the pixel and 0 means exclude it, so by setting the value at 0.5 (the default) it would only include the 1.0 pixels.
You can set the level higher or lower so that you mask in/out different levels of color. You could effectively have a loop ranging from 0 to 0.5 or whatever which would gradually dissolve the image in.
If you use SetAlpha 0.5, then any alpha values in your image that are brighter than `half` will determine which pixels are masked in/out when using it for SetBlend MASKEDBLEND. Usually, pixels in your alpha channel will be either 1.0 or 0, where 1.0 means include the pixel and 0 means exclude it, so by setting the value at 0.5 (the default) it would only include the 1.0 pixels.
You can set the level higher or lower so that you mask in/out different levels of color. You could effectively have a loop ranging from 0 to 0.5 or whatever which would gradually dissolve the image in.