A method of analyzing a thermal image of a coated substrate to determine the presence of defects includes determining a defect temperature range based on a color of the coated substrate and the maximum temperature of the coated substrate in the thermal image. Thereafter, the thermal image is processed by determining a signal value of a pixel of interest based on a temperature of the pixel of interest, temperatures of pixels in a kernel of pixels surrounding the pixel of interest, and the color of the coated substrate. The signal value of the pixel of interest is then compared to the lower temperature threshold of the defect temperature range, wherein the pixel of interest is a defect location when the signal value of the pixel of interest is greater than or equal to the lower temperature threshold.