digital zoom vs computer cropping

[Shinnen]

This question has probably been raised many times, but I would like to find out what the current consensus is.
Is there a prevailing opinion one way or the other wrt IQ; or is it dependent on too many factors to be generally true one way or the other?
Thanks,
..... john

[Ozzie_Traveller]

G'day John
A decade ago with my original Fuji 5000 camera, it offered 10x optical zoom with choices of 1,4x or 1,8x or 2,2x digital zoom. The 1,4x zoom occurred with zero reduction of pixels, the others occurred via dropping from native 3mpx to 2mpx to 1mpx. I loved the 1,4x zoom and shot heaps & heaps of images this way.

What I also discovered was that Mr Fuji also altered the JPG compression as the digital zoom took place, increasing the image quality in the process ... ie: from 'normal' IQ to 'fine' to 'superfine'. Even though it was a 3mpx camera, I had many magazine covers and A4 full page images displayed in damn-good quality. There was no discernable image quality loss on the magazine prints at 600DPI.

Today's Panasonic cameras that we use - the FZ200 & the G2 slr, each offer an option called 'EziZoom' whereby when I drop mpx from max of 12mpx to 6mpx, the camera invokes the Panny 'EziZoom' to extend the optical zoom by 1,4x, and it is something that I use nearly all the time.

So back to your Q
I have printed [via the local print shop] Fuji 1,4x digi-zoomed images to 8" x 12" with zero visible loss of quality; 8" x 12" prints at 1mpx - 2,2x digi-zoom certainly showed pixellation, but not until it was pointed out to the viewer. I have printed Panny G2 slr EziZoom 6mpx images to 20" x 30" with zero visible loss of quality

From the above & for me ... if the camera is saving images in 'best' JPG quality and also digi-zooming you will get a better result than if the camera was saving as 'economy' JPG quality [I take that as a given].

However I have found to my horror that some image manipulation software automatically saves cropped images at JPG 'medium' quality format, while others [like PS/PSE] offer you a scale of 1 to 12 for the saved IQ. This would, I presume, make a difference with the printed result when printed as a 'decent-sized' enlargement.

Where does this take me? With the cameras set to max mpx and 'best' JPG image quality, and using PSE for cropping, I am comfortable cropping in the computer -IF- I didn't manage it in the camera. But as I do enjoy in-camera digi-zoom, I will continue to use it whenever appropriate

Hope this helps
Phil

[TCav]

First, in my dining room are two 8x10 photos hanging on the wall showing my wife competing at different Dressage events. One was taken with a Canon film SLR, and the other was taken by me with my 3MP Nikon Coolpix 880, and cropped to about 2 MP. You need an eye loupe to tell which is which.

Second, in general, digital zoom and image cropping are different methods of doing the same thing. But as Ozzie_Traveller pointed out, different camera manufacturers may have different methods of improving the general image quality of their digitally zoomed images. For instance, in addition to digital zoom, Sony cameras also have a feature called "Clear Image Zoom". What the difference is, I couldn't tell you, nor could I distinguish between images that use it and images that use the conventional digital zoom, but I suspect that the images are processed differently, even though I can't verify the voracity of their claims of improved image quality.

What I can tell you is that you're always better off with optical zoom than with digital zoom in its many guises.

[Shinnen]

Hi Phil/TCav,
Thanks for your help.
I'm trying to discern if my F70exr produces better images by cropping the 10X optical image to 400%, or going with the 10x optical with 4x digital. My initial assumption was that the digital x optical would produce a better result than cropping the optical, because the manufacture would know more about how to blow up the image than any software; but my initial tests suggest that cropping the optical zoom produces a better image. I'll have to do more testing.
...... john

[TCav]

Any in-camera settings for sharpness and contrast could affect the image quality of digitally zoomed images too. So before you go forward with your own testing, I suggest you set those to their default values.

[Hawgwild]

Here's a discussion we had a while back about this very subject, you might find helpful/interesting.

http://forums.steves-digicams.com/so...lear-zoom.html

[TCav]

Thanks for reminding me of that topic.

I'll add one more observation to those I posted in that topic:

The Acutance was increased in the CIZ shots. Unfortunately, acutance tries to pass itself off as genuine sharpness.

[Shinnen]

Well, I took a few shots with the full (10X) optical zoom, then the same subject (a shed with ornaments) with the digital (6x) on top of it (all on tripod).
Then I resized the optical zooms to take in the same area as the optical+digital.
WRT to IQ the digital zoomed has more noise, as evidenced by somewhat brighter edges. They also showed detail a smidge better.
But I think I'll turn off the digital zoom, since they looked a little over processed. All in all though, there's not really a great deal of difference.
.... john

[Shinnen]

Hi Mary,
Thanks for the explanation.
.... john

[Shinnen]

That's good to hear.
..... john