Tech question on imagers

Does anyone know the answer to this technical question:

In camers (like the ELPHs) that shoot movies, the movies are only 640X480. Does that mean they are only using 640 pixels by 480 pixels to capture the movie image, or do they use the whole CCD chip and downscale it in the camera to 640X480.

Also, on a related topic, given that a movie might by 30 frames per second, is the shutter speed for each frame that (slow) 1/30, or is the shutter speed possibly higher (say 1/60 or even 1/250)

Thanks in advance if anyone knows the answers. Also, if anyone knows of a good Q&A site that might be able to answer such a question, that's be really helpful.

They are downsized; you can reason this out for yourself by comparing the coverage of a video with that of a still of the same scene.

And there's not really a discrete "shutter" used during video; just a capture off the sensor at the stipulated frame rate.

Jon wrote in post #5034113
They are downsized; you can reason this out for yourself by comparing the coverage of a video with that of a still of the same scene.

And there's not really a discrete "shutter" used during video; just a capture off the sensor at the stipulated frame rate.

Thanks for responding.

I didn't quite understand, though, the bit on your first response. I think you meant to say that they are only using a physical 640X480 group of pixes, and not downscaling? Or, did I misinterpret

On on the second bit, although I understand there is no shutter, does that mean the pixels are exposed to the scene at a 1/30th second rate? That is, if I could have a camera that does 60 frames per second, and potential blur in a fast moving scene would be reduced??

No, they use the whole sensor and downsize the image to 640x480. If they used a 640x480 crop, it would be like using a telephoto lens; you'd only get a fraction of what a still at the same physical setting would capture.

Yes - the sensor's dumped 30x a second. Newer models offer a 60 fps capability, but with a shorter recording time and/or lower resolution.However due to a number of factors, the actual exposure is somewhat less than that. And due to the way the videos are recorded, I doubt you could tell; remember - they aren't recorded as discrete frames, rather (in a manner analogous to JPEG data compression) as deltas to the previous frame.

Thanks again. The downscaling makes sense. It also should mean that the G9 (with a 1/1.6 CCD) should get better movies than an SD800 (with a 1/2.5" CCD) all other things being equal, because the larger sensor collects more light. And this seems the case in comparing movies from my two cameras (800 and G9).

Regarding movie compression, you are correct for intra-frame compression, but the canons use motion jpeg, which uses only inter-frame compression. Each frame is a Key-frame. So, each frame actually is discreet. This is the same typically with DV and MJPEG, but not for like h264 or MP4, as examples.

I am just trying to figure out how they capture each frame, as some of my movies seem blurry with high action (that is, each individual frame is blurry -- taken together it looks smooth), which would suggest to me a 1/30 sec. exposure time. This is not the case if I shoot the same movie in a traditional camcorder in DV. So, that's the reason for my question re: exposure time in the canons.