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Old Dec 2, 2003, 12:23 PM   #1
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Default digital zoom and megapixels

Hi everyone,

From what I understand the reason digital zoom is worthless is because it just blows up the middle pixels, thus causing a degradation in picture quality. If this would be so, would the problem be less the more mp my camera has? Can I use digital zoom on my 5mp and still get the same quality as a close-up of 2 or 3 mp?

TIA

Shraga
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Old Dec 2, 2003, 12:32 PM   #2
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that would be true but you would still be degrading the image. its the equivelent of cropping an image in a program like PS
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Old Dec 2, 2003, 12:47 PM   #3
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Well, that is one of the main reason for having higher mp's, isn't it? So I guess it would be accurate to say that higher mp's have TWO advantages:

1. You can crop
2. You can use the dgital zoom!
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Old Dec 2, 2003, 12:57 PM   #4
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thats all relevent to the size of image you wish to produce and the quality too.
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Old Dec 2, 2003, 1:18 PM   #5
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I would rather have a 2mp camera with a 3X optical zoom than a 3mp with 5X digital zoom. When you use the digital zoom your quality will diminish.
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Old Dec 2, 2003, 1:49 PM   #6
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Quote:
Originally Posted by gibsonpd3620
I would rather have a 2mp camera with a 3X optical zoom than a 3mp with 5X digital zoom. When you use the digital zoom your quality will diminish.
But that's exactly my question! How MUCH will it diminish? Will it diminish to the point where it's worse than a picture taken by a 2mp camera?

In my case my 5mp has 3 optical and 3 digital zoom. Would I be better off with a 2mp 6 optical zoom? Let's not forget that the 5mp still has the advantage of being able to crop a lot when NOT using the digital zoom!
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Old Dec 2, 2003, 3:57 PM   #7
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I started the same discussion - with no conclusion, a while ago. Basically I said, if you could buy an XMpix cam without much optical zoom, and with image stabilisation, would there be a 'sweetspot' where you had a compact camera with equivalent performance to an optical zoom without the bulk and weight? For those that decry digital zoom, don't forget you might lose geometry distortion which is all to prevalent in optical zoom lenses.

I think the answer is in the resolution performance of a 'standard' lens. You can use 'digital zoom' (with sufficient pixels) until you hit the performance limitation of the standard lens. That's my 3 pence worth! VOX
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Old Dec 2, 2003, 4:15 PM   #8
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Back to the square root.

As an example, if you double the focal length of a lens, you halve the field of view, i.e., equiv to cropping half the linear dimension or using 1/4 of the available pixels. Or the other way around, if you quadruple the pixels, you can crop half the linear dimension and retain the original number of pixels.

In general, the extra "zoom" you gain from more pixels is the square root of the pixel ratio. e.g., going from 3 to 5Mp gives an extra 29% zoom - from 100mm to 129mm equv. To double the "zoom", you have to increse the pixel count by a factor of four.
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Old Dec 2, 2003, 4:17 PM   #9
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Here is a table from Digital_Ray_Of Light, based on formulas described by Rodger Carter and Rick Matthews (Telephoto Figure of Merit: Explanation and Uses) with popular long zoom models.

http://www.geocities.com/digital_ray...oomzoomv3.html

You may find it interesting in comparing resolving power of different resolution models. You'll also see links to formulas and explanations.

P.S. watch out for the pop-up advertisements (apparently his host uses them).

Also, I would personally not use the interpolated results for the newer Fuji models. Reviews that I've seen show no "real" resolution advantage to shooting in the interpolated modes (detail captured).

The older models Fujis were a little better in this respect (with 3 Megapixel Models performing more like 4 Megapixel Models on resolution charts). The denser "4th Generation" Fuji Sensors don't seem to perform as well.

Update:

It looks like the links to the formula explanations are not working now. Basically, it's what Bill Drew is saying. You have to quadruple the pixels to double the equivalent zoom.
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Old Dec 2, 2003, 4:31 PM   #10
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I understand BillDrew's theory. But let's assume the future is infinite megapixel resolution - that's cheap electronics and digital processing. What is the resolution limit of an affordable high quality compact camera 'standard' lens? There has to be a reasonable point (for a compact camera) where increase in Mpix will give no further gain due to optical limitations. VOX
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