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Old Aug 24, 2004, 3:15 PM   #1
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considering they have 4mp/5 i was wondering what the quality of the photos would turn out at 40x for example? i just tested 10x on a olympus (optical) and i expected to be able to get closer, so im just wondering if the quality is bad for digital!
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Old Aug 24, 2004, 5:26 PM   #2
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Hi Joe,

It depends on the field of view. Let's see if we can put it into perspective. When you use digital zoom you are actually cropping to the extent of the zoom then interpolating back to full resolution. When shooting things like landscapes, this would leave you with precious little resolution and the results would be terrible in general, but when shooting closeups such as shots of birds, headshots of animals, etc., there "may" be enough resolution and true detail capture to support the interpolaition.

Interpolation algorithms use existing information to create missing information. This means that when the algorithm encounters "good" data, it simply makes good "larger" data. Providing there was "sufficient" resolution to truly define data in the initial capture, then there are few practical limitations for doing a "digital zoom". On the other hand, if the original capture was lacking sufficient pixels to properly define boundaries of fine detail, then "marker" pixels are created. You may think of marker pixels as "place holders" which mark the position of features, the general shade and sometimes the rough shape, but really only "work" when the enlargement keeps these marker pixels below the threshold of human recognition.

Think of it like an oil painting of a forest with pine needles on the trees, grass, leaves, etc. As long as we don't have to look at a magnification of the painting with a loupe or microscope, we can readily accept a few brush strokes as quite adequate representation of pine needles, leaves, grass, etc. But once we are forced to see it under rather intense magnification, the illusion is shattered and we are forced to see the deception and realize that we are seeing brush strokes rather than what we "believed" these brush strokes to represent.

Interpolation algorithms used during digital enlargement sort of act like the magnifying glass. They simply look at what is really there and reproduce it faithfully but larger. When they find detail, they reproduce detail. When they find marker pixels they simply make larger marker pixels and the illusion is wrecked and we don't like the results.

Digital zoom takes away lots of resolution. When you use a 2x digital zoom, you reduce the size of the image under the microscope by two dimensions. This results in an image made with 1/4 the pixels. So if you start with 4 megapixels, with a 2x digital zoom you end up with a 1 megapixel resolution capture for the portion of the image representing the crop. When the camera interpolates this, it resizes back to the original 4 megapixel dimensions. Now if the area of the capture cropped represents a rather narrow field of view (not too much geographical real-estate) then there may indeed be enough pixels to properly represent the detail.

So, what does this mean in the real world? Let's say you use your 12x optical zoom to fill the frame with a bird and you use digital zoom to get a head and shoulders "portrait" of this bird. In this case you have expended quite a few pixels on a fairly small geographical frame and the chances for a digital zoom being useful is pretty good. But what if you were trying to capture one of a flock of 20 birds at a great distance and the "best" you could do with you 12x zoom was to get the entire flock. Now when you go to digital zoom you may have only 4 or 5 birds in the frame, but you are only interested in one. The results will not be satisfactory. Now carry this to the extreme and let's say you were trying to use digital zoom to try and identify a single individual in a crowd on a yacht far away. The full frame at 12x optical shows the yacht and several other boats, lots of ocean and waves and coast line. No way will digital zoom help you in this case, the "people" on the yacht are only represented by "marker pixels" and there simply will be zero detail in the enlargement.

To get a handle on what "marker pixels" are, think of a scenario like this. Imagine you have a camera with only a 16 pixel resolution. The file would be four pixels high and four pixels wide. Now assume you want to photograph the following:

You have sixteen pure white, plastic, smooth, featureless "discs" to be photographed on a pure black, smooth, featureless plastic backdrop. You zoom in and fill the frame with a single disk and snap the shutter. Sixteen pixels can define the basic shape and color of a single disc and the color of the backdrop. Now zoom out and get all sixteen discs into the frame. Snap the shutter. Now we have a big problem. We have sixteen discs and two colors to "define" but we only have enough pixels to represent "position". This, of course is an extreme example and not truly even "accurate" but it gives you in essence the definition of "marker pixel." All we can do in this case is define position - not even color or shape.

The essence of enlargeability is having sufficient pixels to keep marker pixels below the threshold of recognition at the desired enlargement. The more digital "resolution" in terms of pixel count we have to vest in a given frame, the larger we can blow up the image before reaching the treshold of recognition where we must either stop enlarging or greatly increase viewing distance to compensate and again bring the threshold of recognition below human visual acuity.

Bottom line? Digital zoom is sometimes useful, but is no substitute in any way for optical zoom.

Best regards,

Lin
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Old Aug 24, 2004, 7:58 PM   #3
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thanks lin very imformative and helpful! i appreciate the explanation
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Old Sep 9, 2005, 4:37 PM   #4
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Can I ask for an application to enlarging for prints? If I had a 4mp picture and wanted to enlarge to a 12x16 that would yeild about 150PPI? What is the PPI number were human recognition of the "marker pixels" would begin for the average person? Any ideas?
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Old Sep 10, 2005, 1:18 AM   #5
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not sure about where the average viewer would be able to see "marker pixels", but i've got one print on my wall that started at 5MP, was cropped down to about 3.5MP, then interpolated back up to 5.5MP and printed at 11x14. it came out just fine. granted, it's a close up of a monarch butterfly, but it's still a very clean image.

150ppi is probably the minimum you'd want to use. i've seen prints made from a 2MP camera (FZ1V2) printed at 8x10, and there is noticeable pixelation. interpolating this up to yield 175ppi seems to elimiinate that. most of the time, i try for at least 200 ppi.

a lot of it is literally "in the eye of the beholder". those with extremely good visual acuity may be able to see pixelation up to 175 ppi or more. my eyes aren't what they used to be, and to me, 175ppi produces prints as good as anything i ever shot with my 35mm SLR.


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Old Sep 10, 2005, 11:19 PM   #6
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I think the FZ20 digital zoom is amazing. Took this shot of my son at little league, at about 40X digital zoom, from about 70 yards away.
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Old Sep 11, 2005, 11:58 AM   #7
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corcoj wrote:
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I think the FZ20 digital zoom is amazing. Took this shot of my son at little league, at about 40X digital zoom, from about 70 yards away.
Uhm... The EXIF shows FULL ANALOG zoom - 432 mm equivalent and NO digital zoom.

Ian
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Old Sep 11, 2005, 12:58 PM   #8
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Ian48Harry wrote:
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corcoj wrote:
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I think the FZ20 digital zoom is amazing. Took this shot of my son at little league, at about 40X digital zoom, from about 70 yards away.
Uhm... The EXIF shows FULL ANALOG zoom - 432 mm equivalent and NO digital zoom.

Ian
Well, I'm glad I'm not on trial because this would be one of those Perry Mason moments.:? EXIF info certainly does show no digital zoom. My recollection of the zoom lengh is strictly from memory; but I always sit in the same spot, at the far end of the field and another sixty feet or so to the top of a hill. That's how I approximate about 70 yards to home plate. Either theEXIF is wrong or, if the FZ20 gets that close up with optical zoom from that far away, I'd expect to beable to count the umpire's nose hairs at full digital zoom. In any case, it's a heck of a camera. :-)
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Old Sep 11, 2005, 1:24 PM   #9
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nelmr wrote:
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Can I ask for an application to enlarging for prints? If I had a 4mp picture and wanted to enlarge to a 12x16 that would yeild about 150PPI? What is the PPI number were human recognition of the "marker pixels" would begin for the average person? Any ideas?
It's really not a matter of print dpi, it's more a matter of field of view and subject matter. If your four megapixel original capture was a telephoto image which covered a small field of view such as a full zoom telephoto of a rather close bird or a head and shoulders portrait, etc., you could get an excellent 12x16 print with no visible marker pixels. On the other hand, if your capture were a wide angle detailed landscape, it might even be possible to see them in an 8x10 upon close examination.

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Old Sep 11, 2005, 2:22 PM   #10
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corcoj wrote:
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In any case, it's a heck of a camera. :-)
Now there you and I agree!

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