A photo of sunlight split into spectra was the source image for this Liquib example.  The Bloom Tool has been applied multiple times with the Petal Shape set to Captured Stencil, which bases the Petal shapes on stencils created according to the relative lightness/darkness of the source image.  Also, the Bloom Style was set to Cloned From Image, causing the Petal contents to be copied from the source image.