Sensor defects, like dead pixels or even dust, are difficult to spot during production, but can annoy viewers. Broadcasters have had little option but to perform acceptance tests visually, but “detecting rogue pixels by eye among the six million RGB elements in images from HD cameras is almost impossible”, said Cel-Soft managing director Robin Palmer. High-end cameras are usually calibrated to map defects, and offending pixels can be masked by digitally averaging the signals from neighbouring pixels. “Cheaper cameras use no such masking,” Palmer explained. “In any case, once a camera gets into the studio or the field, pixel defects can appear at any time as a result of age or temperature. “An uncorrected pixel error can show as a coloured or black dots,” said Palmer. “In single-sensor cameras, it can appear as tiny cross because of the way the pixels are spatially sampled.” The Pixel-Probe algorithm automatically generates a statistical log of every pixel. It can then work out, over a short period of fluctuating footage from the camera, if any pixels are not working properly. It also identifies pixel changes since a previous check, or between different shots in post. “The increasing use of digital single-lens-reflex cameras for broadcast and even cinema production, along with other low-cost cameras, will make this sort of test process essential. Bigger and better high-resolution displays are also making uncorrected pixel defects more obvious to television viewers,” Palmer added. Pixel-Probe is compatible with Cel-Soft’s Reel-Check SoloQC live source or file analyser and Cel-Scope 3D realtime stereoscopic test and measurement system. – David Fox10.C49
