Another question about digital zoom (in video mode lossless zoom possible?)

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.

Does anybody know, which of these cases will happen? Or is the
software in these cameras flexibel enough to realize that it can do a
digital zoom without first down- and then upsizing?

If you dont know the answer, perhaps someone could try setting the
picture size to 640x480 and then do a digital zoom, and see what
happens. Thanks.

 

I expect the issue is not that people don't know the answer, but that
your larger paragraph borders on incomprehensible. No offense, I think
it's a useful thing to discuss - but in all honesty I can't make heads
or tails of what you're saying.

However - in my limited experience, digital zoom in cameras pales to
the result you'd get with Photoshop. I'd _never_ recommend people use
digital zoom if they're concerned about quality.

 

Referring to what post? Please leave enough so I can figure out what
you are on about.

 

Umm.

Most cameras only do 640x480 video by default. They don't start at 7mp
in vidoe, only still.

If you digital zoom on top of that, you still get image degradation on
all digial zoom operations. It is only taking the center part of the
image an blowing the pixels up to make the picture closer, while
showing no more detail.

Digital zoom is a marketing ploy, not a photography tool.

Go for one of the new 10 or 12x zoom cameras if you want to zoom,
digital zoom is a cheap gimmick.

 

Options instead of falling for "digital zoom" aka - cropping down to a
crappy image.

Fuji s5100, has a 10x OPTICAL zoom. It only starts at 4.0MP but please
don't fall into the Megapixel trap. You sound like a amatuer user, so
you'll not really need to have the extra millions of pixels to print
your 5x7's. Or even 8x10s. You might need 7MP for a 11-1/2x14 or
larger.... $250 from Amazon.com

The Canon powershot S2-IS is Probably your best choice, but is $450.
You get 5MP, 12x optical zoom, Image stabilization (I love this BTW,
totally worth the extra $$). THe Sony DSCH1 is VERY similar to this if
you like. Same price.

Go to dpreview.com and steves-digicams.com for some reviews.

 

: 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

 

I understand and agree with all you wrote. My motivation for my
question is this: The ex-z750 can not do optical zoom in video mode,
but it can do digital zoom, up to a factor of 4. S o I dont really
have a choice.

And, concerning processing power of the camera chip, I think it would
be very easy to just change the pixel-skip for digital zoom. As you
said, when the camera scales down from 3072 hirizontal pictures to
640, it will - so you assume - take only every 4th or 5th pixel from
the original 7MPixel picture. I I swith on digital zoom in this case,
the processor on the camera could perhapps take every 2nd or even
every pixel from the central area of the original 7M picture to achive
an enlarged digital zoom in 640 mode. Not much more processing power
required here.

But all that is theory, we dont know what the camera's imige processor
will do. Or has anybody tried it already?

 

I cannot see the point of trying to use my camera as a video camera
when a video camera does the job so much better. In my household my
wife and son do the video and I stick to stills.

 

Klausa,

Get it through your head.

It's not theory. You take a 640x480 video, apply a 4x digital crop
(stop calling it zoom, it's not) and you're enlarging a 160x120 section
in the middle of the screen. Get over it. This idea of yours does not
work.

You need a camera that does optical zoom while shooting video. Wrap
your head around the idea. Get comfy. Go save whatever money that you
need to buy whay you need. Or just buy this camera (because you have
obviously convinced yourself that you have to anyways) and stop buggin
out.

 

I don't think so. My understanding is that a digital camera always shoots at
its full (maximum) resolution, regardless of the resolution setting, and
then downsamples as necessary for a lower resolution image.

I think that's right, but his question is interesting because it should be
*possible* at least to keep the same resolution while digital zooming (to a
limited extent) by doing the downsampling (if any) after the digital zoom,
as he suggests.

My guess, though, is that digital cameras generally don't do that, and even
starting at 640x480 you'd begin immediately to get image degradation with a
digital zoom. I'll have to try that and see.

If you started at full resolution, yes.

But not if any downsampling occurs *after* the digital zoom, which is what
he's asking about.

Without having tried it yet, though, I'm inclined to agree with you; I don't
think digicams do it that way.

Depends. It's not of *much* use generally, that's true. However, if the
camera is tripod-mounted to avoid shake and the image is going to be viewed
only on a computer screen, which is relatively low resolution anyway,
digital zoom can be very useful. I have gotten some nice shots of birds
nesting in a tree outside my window that way, much more satisfactory than if
I hadn't used digital zoom. I wouldn't bother printing those shots as I'm
sure they wouldn't be sharp enough for that purpose, but on a computer
screen they're fine. And many people do view most of their shots that way,
on a computer monitor.

I suspect "the majority of people" who say digital zoom is worthless, say
that just because that's what *they* hear the majority of people saying, but
haven't tried it themselves (or tried it only hand-held, which is bound to
be a disaster). I would agree it's mostly an advertising gimmick, but it's
not worthless.

N.