Posts Tagged ‘Propeller Distortion’

Now days, everyone with a digital camera considers himself as a professional. No doubt I also have a love for photography. So I thought putting something about sensors used in cameras on the blog. Most digital (rather almost all) use sensors from CMOS family or CCD family.
Both the technologies keep on improving. CCD (charged coupled device) may be better from CMOS (complementary metal oxide semiconductor) in one aspect while CMOS might be better in another. Each has unique strength and weaknesses.
Both these sensors convert light into electric charge. In a CCD, every pixel is transferred through a very limited number of output nodes (often just one) to be converted to voltage buffered, and sent off-chop as an analog signal. All of the pixels can be devoted to light capture, and the output’s uniformity is high. In CMOS, each pixel has its own charge-to-voltage conversion, and the sensor often also includes amplifiers, noise-correction, and digitization circuits, so that the chip outputs digital bits. With each pixel doing its own conversion uniformity is lower.

But the point why I am concerned about the sensor is little application dependent. Let’s understand it. Now suppose I have a camera on a plane taking images of propeller regularly. Both kinds of sensors produce different types of distortions or artifacts when they click images of rotating propeller.
In one of the form, the image contains curly rippling lines while in the other it produces a sort of a propeller which keeps moving in consecutive frames. Curvy image is generally produced by CMOS sensors. While the other distortion is produced by CCD sensors.

These artifacts are majorly due to different e shutter methods used. CMOS sensor uses a rolling e-shutter while a CCD sensor uses an uniform e-shutter. To get a better image fps could be increased. It is seen that at a particular fps rate, sensor produces images showing stable propeller even though it is rotating. SO now i know what I am going to lose (or gain) if i use a CMOS based camera with low fps rate.
So this was propeller distortion. This is a major concern while talking about the aerial image acquisition.