Abstract　 　　
　 We demonstrate that, for galaxies, the total flux in Spitzer IRAC 8 um (dominated by emission from Polycyclic Aromatic Hydrocarbons or PAHs) or MIPS 24 um (dominated by emission from very small dust grains or VSGs) band can be decomposed into two components, a "warm" component that scales with the flux of some independent measure of current star formation, and a "cold" component that scales with the flux of a measure of diffuse emission from cold large dust grains. Application of this to a large sample of IRAS galaxies shows that the warm PAH component dominates only in IR-warm galaxies of starburst characteristics. With the newly available Herschel SPIRE images at 250 - 500 um, we apply this method to the disks of nearby large galaxies, using (a) the SPIRE fluxes as measures of cold dust continuum emission of large dust grains heated by evolved stars and (b) H-alpha line emission as a measure of current star formation. As an example, we show that in the case of M81, about 67% (48%) of the 8 um (24 um) emission derives its heating from evolved stars, with the remainder attributed to heating by radiation field associated with ionizing stars.