cmos rolling shutter--i assume they can't just make them like this... at DVinfo.net

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Old July 2nd, 2010, 03:56 PM   #1
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cmos rolling shutter--i assume they can't just make them like this...

would it be possible for a cmos chip to scan random pixels instead of going down the frame line by line? let's say that the cmos sensor has 1920x1080 pixels. when it scans line 1, it's scanning 1920 pixels, line 2--another 1920, until it gets down to the 1080th line at the bottom. right? maybe not, but that's how i understand it.

so why can't the chip scan 1920 random pixels at a time, like maybe it scans 34 pixels of the first line, 13 of the second, 182 of the 19th line..i mean you could come up with some kind of pattern or something so that it scanned 1920 pixels 1080 times per frame but never did it the same way twice in a row.

that way, when you moved the camera from right to left really fast, instead of vertical things coming out diagonal, wouldn't they just look blurry? or maybe it would look really weird and cause a whole new set of problems.

i assume that if it were a good idea, it would already be happening, so what makes it impossible/impractical?
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Old July 3rd, 2010, 05:56 PM   #2
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because that would result in a ridiculously distorted image, with some pixels duplicated, but mostly you would have what would normally be motion blur or skew blur randomly found as noise everywhere in the image.

add to the fact you cant really record random pixels at will; they scan line by line, so you would not really be able to randomly scan 1920 pixels.

on the other hand, perhaps if they scanned VERTICAL lines, the effect would not be so great, as most pans and action tend to be horizontal.
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Old July 3rd, 2010, 08:43 PM   #3
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yeah scanning vertical lines would eliminate the scew/wobble issue for pans, but i guess you could still get the effect where you're 'racing' the sensor--so it scans some things repeatedly or not at all. seems like that would require faster movement though so it would probably be less common.

so if you could make the scanning mode switchable from horizontal to vertical with a button or something, you could pan and tilt fast without worrying about wobble.

i suppose the real solution would be to make the chip just scan faster (a complete scan takes 25ms i think?), so you couldn't move fast enough to distort the image. i don't know. they'll figure it out.
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Old July 4th, 2010, 02:32 AM   #4
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The higher end cameras have a high refresh rate, so you get much lower skew levels. It didn't seem that noticeable on some scenes I saw from the Arri Alexa, when they were tracking along a fence made up of vertical posts.
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Old July 10th, 2010, 09:34 PM   #5
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Yeah, the $10k and below you have to really test first. Panny HPX-300 is fairly worthless at 1080p, but quite good at 720p for instance. the Sony EX1 and EX3 seem to be pretty good, if you want a 6-8 palm corder...(I don't) where you looking at a price range or just a general question about Cmos?
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