Re: Another question about digital zoom (in video mode lossless zoom possible?)
- From: Randy Berbaum <rberbaum@xxxxxxxxxxxxxxxxxxxxxxx>
- Date: Sat, 30 Jul 2005 04:28:25 +0000 (UTC)
klausa <iIdont@xxxxxxxxxxxxxxx> wrote:
: I am considering buying the Casio EX-Z750, a 7MPixel camera. The
: picture size is 3072 x 2304. Now, If I do a digital zoom of say 3, my
: effective Picture size will be 1024 x 768, but will be recalculated to
: 7 MPixel. Of course, the picture contains no more information than
: 1024 x 768. So, by using the digital zoom, I will loose information.
: BUT WHAT IF....
: I use zhe camera in 640 x 480 mode all the time? That is the video
: mode of the camera. In that case the camera has to downsample all the
: time from 7 MPixel to 307KPixel. And if I use the a digital zoom of 3
: the effective picture size is still larger than 640x480, so, the
: camera COULD do a digital zoom without loosing information, relativ to
: my choosen size of 640x480. But the camera may be too stupid to do
: that. Perhaps it will downsize to 640x480 first, because that is the
: chosen format, without loosing information. And, if I then use digital
: zoom, will start upsizing again from a fraction of that 640x480
: picture, giving an effective information of less then 640x480.
I don't know for sure, as even when I had a camera with digital zoom I
never used it, but my impression is that to make the 640x480 image the
camera only looks at a percentage of the pixels (every 5th pixel and every
5th line for example). This is done before any digital zoom is applied.
Thus if you have a setting of 640x and then do a d-zoom that takes the
center portion of the image and expands the pixels there to reconstruct
the 640x dimensions. So you would have a low res image cut down to even
more low res.
So lets put this all in the same terms. If you take an image at the
highest res and crop to just the 640x480 pixels at the center of the image
you have just completed the majority of what a d-zoom does. So if you
apply this same effect to a 640x image you have cropped down to the center
120x pixels. This is all the image info that has been collected. In either
case the camera then processes the resulting crop to expand it to fill the
original dimensions, but the true captured data is still only the smaller
pixel count. Now concider that the computing power of the chip in the
camera that does the expansion is many times less powerful than the
processor in your home computer. Also this processing must be done in a
very short period of time in the camera (as long processing delays make
photogs nervous), while doing the same thing on your computer can be done
for a longer process with less frustration. So the process in the computer
will be likely to give a much more smooth and acceptable "expanded" image
than the camera (greater processing speed + Longer processing time tends
to give a better resultant image). Even tho they both are doing
essentially the same thing.
This is why the majority of people I have talked to, that take their
photography serious, count d-zoom as a gimick that has little or no use.
About the only use I have used it for is as a way to zoom into the image
for aiming accuracy (as an enhanced viewfinder), but then zoomed back to
the max optical zoom only for the actual photo capture.
Of course now that I am mostly working with my DSLR and my lens selections
give me the range of about 43x optical zoom (over a series of zooms). :)
Randy
==========
Randy Berbaum
Champaign, IL
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