o-Chloro-hexaarylbiimidazole (o-C1-HABI) can be sensitized efficiently by cyanine dyes, the cyclopentanone and cyclohexanone dyes, when exposed to xenon lamp (use filter cut λ _< 400 nm). The photoreaction between the photoinitiator and the dyes was completed through an electron transfer process. Excellent results have been obtained in photoimaging studies, e.g. the resolution of the image can reach 7 μm. The influence of the content of the dyes and the heat after the exposure on the resolution of the image was investigated.