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-   -   Digital Zoom - does it exist? (https://forums.steves-digicams.com/newbie-help-16/digital-zoom-does-exist-21765/)

sstarless Mar 7, 2004 2:34 PM

Digital Zoom - does it exist?
 
When I take picture in maximum optical zoom and maximum optic plus maximum digital zoom and compare them in Photoshop both as their actual pixel sizes, they are absolutly same magnification (object size). Just the view is narrowed to the object in digitaly zoomed picture. So where is the digital zoom if both are the same zoomed?

iason Mar 7, 2004 2:47 PM

As I know, technically there is no much difference between digital zooming and zooming in PhotoShop. That's why value of optical zoom is much more important and a matter to be concerned.

Mr_Saginaw Mar 7, 2004 2:48 PM

Quote:

Originally Posted by iason
As I know, technically there is no much difference between digital zooming and zooming in PhotoShop. That's why value of optical zoom is much more important and a matter to be consirned.

That's exactly right... digital zoom is just like cropping on your pc... I have digital zoom TURNED OFF on all my cameras/video....

azpatrick2000 Mar 7, 2004 3:30 PM

Digital Zoom is 1) a selling point for the unaware or 2) for those that do not have (or use) photo editing software.

slipe Mar 7, 2004 5:18 PM

You will not get that result with all cameras. There is at least one 5Mp digital camera that will upsample the digital zoom shot back to 2560 X 1920. Therefore the object would be twice the height in pixels with a 2X digital zoom. I havenít bothered to take a digital zoom shot with my other cameras as I would prefer to crop and upsample myself, so I donít even know how they do it.

Some people claim there is a small advantage to the camera doing an upsample before it adds compression artifacts. The disadvantage is that it is taking up 4 times the space on a card as a 2X zoom shot would without upsample.

With either method you would get only 1Mp of resolution on a 4Mp camera using a 2X digital zoom. It is basically useless either way.

sstarless Mar 8, 2004 8:19 AM

Thanks for response guys but exept of "slipe" you are not exactly answering my question. Basicaly my problem is that when i take a picture without using digital zoom and look at it in fotoshop as its "actual pixels size", do I look to a digitaly zoomed image? Buecose if not then why my picture taken using digital zoom is of the same size?

JimC Mar 8, 2004 11:14 AM

The size of the photo in pixels with optical zoom versus digital zoom will be the same in most cameras (because Digital Zoom crops the photo, then interpolates it back to the original resolution).

This degrades quality, because the detail captured is only equal to the amount of detail captured after the cropping.

You can do the same thing with software later.

PKchopper Mar 8, 2004 4:48 PM

Quote:

Originally Posted by sstarless
Thanks for response guys but exept of "slipe" you are not exactly answering my question. Basicaly my problem is that when i take a picture without using digital zoom and look at it in fotoshop as its "actual pixels size", do I look to a digitaly zoomed image? Buecose if not then why my picture taken using digital zoom is of the same size?

the pictures in fotoshop will have the same exact number of pixils regardless of zoom or not. If you take a 5mp picture you have a 5mp picture, regardless if you took it with a fish-eye lens or a telephoto lens. The number of pixels do not change.

The digital zoom basically crops the picture then stretches (or upsamples) it out to the same number of pixels. The ratio of pixels, say 1024x768, is preserved but the new digitally zoomed 1024x768 picture should only show the middle of the non-zoomed picture.

I'm starting to confuse myself...I hope you get the idea.

slipe Mar 8, 2004 9:39 PM

I think some digital zooms do work the way sstarless describes without interpolating the image back. If his object size remains the same in pixels regardless of digital zoom then his camera is not doing the upsample. I have read other comments by people who found that an advantage of digital zoom is that their memory card gets a smaller file and doesnít have to store the part of the image they donít need. I donít know whether that is based on observation or their idea of how they think it should work.

But if the height of a person taken with and without digital zoom comes out to the same number of pixels it is obvious that the camera is not resampling back to the full Mp of the camera. With my camera that resamples, a person would be twice as many pixels tall after the camera resampled back to 5Mp using 2X digital zoom compared to the same shot without digital zoom.

Whether the camera resamples or not you still get only ľ the actual resolution with the 2X digital zoom. There might be a slight resolution disadvantage to resampling a compressed JPG yourself in an image editor compared to the camera resampling the raw data before the compression, but I doubt you could see it.

It would be easy enough to check the file sizes. If they are roughly the same the camera resampled back to full Mp. If the file is much smaller (like a quarter) it didn't.

JimC Mar 9, 2004 7:42 AM

Quote:

Originally Posted by slipe
I think some digital zooms do work the way sstarless describes without interpolating the image back.

Newer Sony models have a "smart zoom" feature that works this way (crops only, with no interpolation). It's only available in lower resolution modes (because the image size you end up with is simply a crop from the center of the larger image).


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