Different from traditional electrical readout infrared imaging, optical readout infrared imaging system readout the thermo-mechanical response of focal plane array via visible light. Due to the different parameters of the optical system, usually，the infrared thermal image pixel corresponding to the thermal element of focal plane array is not consistent. And the substrate-free focal plane array brings thermal crosstalk, the image blur. This manuscript analyzes the optical readout infrared imaging principle, proposes an one to one correspondence method between the infrared thermal image pixel and the thermal element of focal plane array, optimizes the digital infrared image by the thermal crosstalk on substrate-free focal plane array. Simulation and experiments show that the algorithm can effectively enhance the contours of the infrared image detail, enhancing image quality.