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-   -   crazy idea...digital zoom (https://www.dvinfo.net/forum/open-dv-discussion/41673-crazy-idea-digital-zoom.html)

Robert Mann Z. March 23rd, 2005 10:46 AM

crazy idea...digital zoom
 
i'm in the market for low cost pocket dv camera, shopping around and looking at features has been fun, its much easier to buy high end stuff due to the limited choices...

after going through my 8th choice i noticed all the cams have stupid digital zoom ratings, really absurd figures, so i tried some out...if the optical zoom is 10 and you zoom to 11 the image looks bad on a cam thats getting a little over 700 lines of resolution...

my crazy idea is this, it seems all the cams do the digital zooming after the image has gone through compression...

why not digitally zoom before compression for a cleaner image, i cannot be the first one to mention this...?

Mathieu Ghekiere March 23rd, 2005 11:39 AM

I think I'll be wrong, as I don't know a lot about it, but isn't that just the principle from the digital zoom what sets it apart from a optical zoom? That you don't zoom with the lens, but IN your image?
And dv is compressed, so I wouldn't know how they would zoom before compression. I think either way it looks bad.

But, as I said, I don't know really much about it, it's just what I think, probably someone will proove me wrong here.

Ed Smith March 23rd, 2005 12:46 PM

Mathieu you’re right.

The optical zoom, as it suggests uses optical lens to zoom in and out mechanically. Therefore the resolution from the widest point to the telephoto point will (should) be the same.

The digital zoom simply 'crops' into the image at certain increments, giving the illusion of zooming. Therefore the more you zoom in, the more the picture quality reduces.

Robert Mann Z. March 23rd, 2005 02:12 PM

it is my understanding that the image a ccd reads before compression is huge, you can very easily zoom in on a hig rez 2 or 4 meg image with no loss of resolution down to ntsc spec...isn't that what http://www.reel-stream.com/ is all about

...pretty soon we will liquid lenses anyway, but one can question

Jack Smith March 23rd, 2005 07:35 PM

I believe I read that they do , do the zoom prior to compression.
a progressively smaller area of the ccd is used to image then the image is stretch to the full screen size.But as digital zoom is incresed the effective pixel count diminshes.
Turn off the digital zoom, it's not very useful at present.I think finding a camera with better optics and no digital zoom would serve you better

Brandon Greenlee March 23rd, 2005 08:03 PM

I found a hi8 camera the other day with 990x digital zoom on top of a 12x optical.

What does that work out to.... like 20 lines of resolution?

Jimmy McKenzie March 23rd, 2005 08:07 PM

I suppose this point cannot be stressed enough since even some pro-sumer cams have digital zoom built in. I think it is a menu option on my xl1's but I forget.

The operative word in the preceding sentance: "forget"

Forget digital zoom. Just like vacuums that can pick up bowling balls, this is a silly size war among marketing departments at the various companies. Compressed dv is already soft enough.

Boyd Ostroff March 23rd, 2005 08:19 PM

But Robert was talking about inexpensive 1 chip cameras, and as he notes, some of them have pretty high resolution CCD's now. It's worth taking a look at the digital zoom on these, there's a chance it might actually be useful. Remember an NTSC frame only needs about 350,000 pixels so you have some room to play on a 3,000,000 pixel CCD.

Jimmy McKenzie March 24th, 2005 06:59 AM

Mostly agree...
 
Absolutely correct on the math Boyd. No argument here. But it comes down to the technology in place to capture the image in the first place. My digital camera was one of the first out of the gate at 8 megapix, and at 1300 bucks it looked like a decent buy. It is garbage. This is a paperweight useful only for vacationers.

So for a 2 megapixel array with a single cmos chip picking up the image from plastic? or sub-prosumer glass, me thinks that the result from pixel panning or re-sizing will offer little benefit.

I guess I'm more in the camp to pay a little more and get closer to how the pros work. But for holidaying and other not-for-production purposes, there is obviously a market need for this kind of tech. Otherwise they wouldn't offer it.

Boyd Ostroff March 24th, 2005 07:18 AM

Oh I agree that pixel count doesn't mean much if it isn't part of an overall good design and decent optics. Plastic lenses in and of themselves don't have to be bad... quite a sizeable part of the population sees the whole world through plastic glasses or contact lenses!

I really don't have any experience with these cheap camcorders, so I don't know how well they implement things like digital zoom. But higher pixel count CCD's can offer real benefits, especially in shooting 16:9 at full resolution. I have a Sony PDX-10 which uses three CCD's with about 1 megapixel each. This gives terrific 16:9 quality. And the digital zoom effect - while no match for optical - is pretty well implemented and I've found it handy a couple times for doubling the image size. Of course you can do this in post, but I think you gain a bit by performing the scaling prior to DV compression in the camera.

As always, "your mileage may vary."


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