Red rolling shutter redux

fans.jpgThere’s been a bit of discussion about the image distortion caused by the scanning (rolling) shutter used by CMOS chips which are starting to proliferate in the prosumer and professional video camera world. The key problem, as I have mentioned previously, is that the scanning imaging device is no longer sending the image solely to scanning displays- i.e. tube televisions. Today’s displays include plasma, LCD, DLP, OLED, etc. Most are progressive, but some include circuitry to display the image as if it were a scanning device.

Confused yet?

Mike Curtis, of HD For Indies, is very heavy into RED usage and promotion on his web site. RED is the video camera that I will agree is changing, or will change, the hardware business in the video industry. I checked in with Mike about the “rolling shutter” issue…

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Rolling shutter? – Pick the right tool for the job.

cmos.pngAt DVXuser, there’s a detailed article called Sensor Artifacts and CMOS Rolling Shutter by Barry Green. He discusses, and does a very good job at showing a phenomenon whereby the image captured by a camcorder’s imaging chip is not gathered all at once (what I’ll call “progressive” like a frame of film behind a shutter) but may end up being collected across the chip like a farmer collecting corn from his field. This can create footage that has unique problems. He says:

While CMOS and CCD sensors do the same basic job (gathering light and turning it into a video image), they go about it in different ways, and the differences can have very significant impact on your footage… CMOS sensors (equipped with “rolling shutters”) can exhibit skew, wobble, and partial exposure; CCD sensors are immune to those effects. And a CMOS sensor with a “global shutter” would also be immune to them, but since no current CMOS camcorders are equipped with global shutters, a camcorder buyer needs to be aware of what the implications of a rolling shutter would be.

As I read through his article, I thought back to using tube video cameras.

Continue reading “Rolling shutter? – Pick the right tool for the job.”

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