NOISE-ANALYSIS IN REAL-TIME PORTAL IMAGING .1. QUANTIZATION NOISE

The limit at which quantization noise becomes dominant in video-based real-time portal imaging has been studied. Quantization noise due to t runcation in integer frame averaging is shown to be dominant over the input analog-to-digital converter (A/D) quantization noise, unless ima ge addition is used in video-based real-time portal imaging systems. P ortal images acquired with the Newvicon camera by averaging more than 64 frames are found to be dominated by the quantization noise due to t runcation. It has shown that the signal-to-noise ratio (SNR) is limite d to 886.8 when using an 8-bit A/D with digital frame averaging, but h igher values can be achieved with digital frame addition. It is also s hown that digital frame addition together with 16-bit processing can a chieve higher contrast resolution than digital frame averaging and 8-b it processing.