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Context<\/h2>\n\n\n\n
If an object were stationary, and one wasn’t in a hurry, one could just do a longer exposure in order to achieve an ideally saturated image. But the object in question is in fact moving. And it’s a line scan<\/a> application. Each line exposure is extremely fast, so there’s not much opportunity to accumulate sufficient light into the sensor.<\/p>\n\n\n\n Use “faster” sensor that is more sensitive in low light situations?<\/strong> Conceptually plausible but not always available relative to speed of motion and available light.<\/p>\n\n\n\n Introduce artificial light?<\/strong> Usually one already adds concentrated light with line scan, but for challenging applications it may not be sufficient… relative to the speeds one hopes to attain.<\/p>\n\n\n\n Use Time Delay Integration (TDI) to build up final image as composite from multiple exposures carefully synchronized to object’s motion.<\/strong> Key concept: the object is moving anyway, so take advantage of that movement as an opportunity to get multiple “looks” at the same slice of the object. A variation on “when given lemons make lemonade”.<\/p>\n\n\n\n See the video below for an illustrative simulation. The conceptual application is mail processing, where the goal is to read whether a letter is stamped, with which denomination of postage, all while the letter is moving at continuous speed along a conveyor belt, lit only by ambient or low intensity light.<\/p>\n\n\n\nCandidate solutions<\/h2>\n\n\n\n