microcapsules 14 are not visible to the unaided eye since the mean size of the microcapsules generally ranges from approximately 1 25 microns exposure of the imaging web 10 by transmission imaging is shown in fig1 b a source of radiant energy 22 is positioned above the surface of the imaging web 10 with a mask 24 positioned therebetween as illustrated the substrate 12 is opaque and the photosensitive material within the microcapsules 14 is a positive working radiation curable material i e the viscosity of the material increases upon exposure to actinic radiation the radiation of the exposed areas 26 causes the radiation curable composition in the internal phase 16 of the microcapsules 14 to polymerize thereby gelling solidifying or otherwise immobilizing the chromogenic material and preventing the chromogenic material from reacting with the developer material 20 to simplify the illustration internal phase 16 39 in the exposed areas 26 is shown as a solid whereas the internal phase 16 remains liquid in the unexposed areas 28 the imaging web 10 is next processed by subjecting the imaging web to a uniform rupturing force by means of a pair of pressure rollers in resilient pressure engagement with the imaging web along a nip the imaging web is moved between the rollers such that the rollers supply a uniform force to substantially the entire width of the imaging web to rupture the microcapsules 14 such that the chromogenic material contained within the microcapsules 14 or otherwise associated therewith can interact with the developer material 20 as shown in fig1 c the necessary developer material 20 is formed as a layer of developer material on a separate substrate or receiver sheet 32 the receiver sheet 32 is aligned and in facing.