Grey-level Vision Sensors

Friday, November 10th, 2017 - Photoconductors, Transducer/Sensor

Grey-level Vision Sensors

This class of sensor produces an output image whose pixel values are quantized into a number of discrete levels, achieved by converting the optical transducer analogue output into the appropriate number of digital levels.

An alternative to this method is necessary when using a DRAM camera as the imaging device because its output is inherently binary; a grey-level image can be produced with the help of some computing power (either within, as in the case of intelligent sensors, or without, by using the vision system main computer). This procedure is based on processing an appropriĀ­ ate number of binary images obtained using different exposure times, whose difference provides a measure of each pixel intensity in the object image.

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Figure 1. Example of grey-level image

Figure 1 shows the typical grey-level image of a bicycle chain link using eight intensity levels as provided by a 2-D grey level vision sensor based on a 256 x 128 cells DRAM camera. A comparison of this image with the one obtained using a binary sensor, shows how grey-level vision sensors (in conjunction with reflected illumination) provide more details of the object surface features. This, however, increases the amount of visual data and makes its processing more difficult, slower and computationally more expensive.

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