A new high speed thermal imaging concept based on a logarithmic CMOS imager technology

ABSTRACT HDRC “ (high dynamic range CMOS) allows for more than 120 dB signal range in image processing. Scene details with both very high and extremely low radiant flux may thus appear within the same image. Color constancy over the entire signal range and good high speed performance are further asp ects of this logarithmic imager technology. These features qualify HDRC “ cameras for thermography, since the signal range of Planck’s temperature radiation in a two dimensional array is comparable to HDRC’s intensity range. Especially in material welding and laser cutting processes, in high power light sources and in high temperature material processing, fast monitoring of the spacial and dynamic temperature distributions present a challenge to conventional thermal imaging and thus call for innovative concepts. A particular challenge is in the compensation of th e emissivity of the radiating surface. Here, we present a new concept based on a modified HDRC “ VGA color camera, allowing for visualization and measurement of temperatures from about 800 °C up to 2300 °C. The modifications include an optical filter for minimizing UV and IR straylight and a notch filter for clipping off the green optical range in order to separate the blue and red RGB regions. An enhanced and adapted software provides a division of the neighboured red and blue pixel signals by means of simply subtracting the HDRC