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 Post subject: Video on Sensors
PostPosted: Sun Feb 21, 2010 9:43 pm 
I can't seem to find a direct description or diagram of this by Googling, so if somebody can direct me to material on it, or explain, I'd be most grateful.

When a digital still-image camera uses a video mode, the frame size is much smaller than the largest still image size available. Is the camera then using just a small area of the sensor, or does it use the whole sensor, but a very reduced number of pixels?

The question arises when comparing video from a camcorder, with a very small (comparatively) - sensor, and video from a still-image camera, at about the same frame size. The video from the camcorder seems to be of rather better quality, despite the smaller sensor.

Thanks, Dave.


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 Post subject:
PostPosted: Mon Feb 22, 2010 7:59 pm 
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One immediate giveaway if it were a crop would be a correspoding reduction in the field of view - like a digital zoom. So if you see no reduction when switching from stills to movie mode, then it's certainly using the full sensor width and height - well obviously some of the height is cropped for a 16:9 aspect ratio, but you know what I mean.

I've noticed some cameras slightly reduce the field of view in their movie modes, but not by a great deal, so it implies most of the sensor area is being used.

The question then is whether the movie mode ignores pixels it doesn't need to deliver a lower resolution video frame, or bins them for higher sensitivity. Hopefully it's the latter, but the manufacturers are always cagey about giving out the full details.

As for a camcorder being better quality, what are you describing? Noise, resolution, something else? And are you comparing it to a DSLR with video, or a compact camera movie mode?


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PostPosted: Mon Feb 22, 2010 10:18 pm 
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I know for a fact that Nikon DSLRs drop every 8th line from the sensor to further decrease the output size, which results in massive stairstepping.

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