Just a historical or nostalgic addition: The Outline Object effect in combination with an additional fill and the Offset Path effect once was the only speedy way to apply correct Drop Shadow effects to transparent raster images as the Outline Object effect was (and still is) able to detect transparent (or non-transparent) areas inside transparent raster images. You can still create an appearance set to see how those drop shadows could be done in former times (Illustrator 9, 10 and probably the first version of Illustrator CS as well). For example, draw a filled heart, then draw a filled circle on top of the heart, select both and create a compound path. Go to Object > Rasterize and choose the Transparent Background option in the Rasterize dialog. Add a new fill to the rasterized heart with a hole and drag that fill below the image item in the Appearance palette. Apply the Outline Object effect to the additional fill, then apply the Offset Path effect to the fill and take a small negative offset value (-0,5 mm for example). Apply the Drop Shadow effect to the fill. Save the entire appearance set as a graphic style, so that you can apply nostalgic shadows to other transparent raster images in the future.
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