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Old Jun 9, 2005, 4:12 PM   #1
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So far, my attitude so far has always been "digital zoom is just crop + zoom, don't bother".

However, I recently learned about the Genuine Fractals plugin for Photoshop that allows to zoom up to 700% WITHOUT IMAGE QUALITY LOSS! Hence, with my S1 IS, if I would take pictures at maximum optical zoom 10x (380mm equivalent) then apply GF to the maximum and crop the image again, I end up with a picture corresponding effectively to an image taken with a 2660mm (equivalent) lens!

Am I missing something here?

Instead of putting teleconverters in front of my lens, should I just wait until I process the pictures to get that full-frame-shot of a critter?
Sure, the software is expensive but hey, that's what a teleconverter would cost, too...

http://www.lizardtech.com/products/gf/overview.php
http://www.imaging-resource.com/SOFT/GF/GF.HTM
price: $160

How would using 3x digital zoom, scaling up with photoshop (bicubic of course), scaling up with Genuine Fractals and adding a teleconverter lens compare in terms of image quality?
Any thoughts?
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Old Jun 9, 2005, 6:07 PM   #2
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If you crop an image to make it look like you used twice as much optical zoom, you end up with 1/4 the original resolution.

Sure, you can interpolate it to reduce pixelation. But, that does not increase the detail captured by the sensor.

Optical zoom does increase the detail captured (you'll have more pixels representing your subject that are captured by the sensor).

Not losing quality, and adding more detail (as optical zoom does) are two different things. If you don't have enough pixels representing your subject to begin with, interpolation is not going to help. It's only adding pixels based on the values of adjacent pixels, and cannot increase the detail captured. BTW, 700% without seeing some degradation is "pushing it".

I've seen quite a few comparisons of interpolation algorithms, and I would expect to see a negligible difference between Genuine Fractals and other commonly used algorithms like Bicubic, provided you were resampling in small steps up.

Read through Lin Evans post in this thread for an explanation of why some subjects interpolate better than others:

http://www.stevesforums.com/forums/v...mp;forum_id=23



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Old Jun 10, 2005, 1:57 PM   #3
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JimC, thanks a lot for your very clear explanation! Makes perfect sense now.

One question that is still puzzling me though is why do people use digital zoom on their camera at all? Is there any situation that justifies using it?

I can only think that it's for people that do not want to process their images on a PC, but in terms of quality wouldn't it always be better to take the picture
at full optical zoom and then "zoom in" (if really needed) by scaling up and cropping with Photoshop/GF/whatever?
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Old Jun 10, 2005, 2:16 PM   #4
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MCSmarties wrote:
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JimC, thanks a lot for your very clear explanation! Makes perfect sense now.

One question that is still puzzling me though is why do people use digital zoom on their camera at all? Is there any situation that justifies using it?
I personally don't use digital zoom. But, there are some people that like it.

Somecameras do seem to have pretty decent interpolation algorithms now. Also, some claim better metering using Digital Zoom (the theory being that only the cropped portion of the image is being used forexposure and white balance purposes).

The other claim is that since the cropping and interpolation may be happening prior to JPEG Compression, theoritically, Digital Zoom could provide better results.

My thought is that you have more control over the cropping process later (more accurate cropping for composition purposes, based on the print/viewing sizes needed), versus trying to get it right with Digital Zoom while shooting.

You can use a much more powerful PC to do the interpolation (with a wide variety of algorithms and techniques available), versus the camera trying to perform this processing in a split second.

So, to each their own. ;-)


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Old Jun 13, 2005, 12:49 PM   #5
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Quote:
However, I recently learned about the Genuine Fractals plugin for Photoshop that allows to zoom up to 700% WITHOUT IMAGE QUALITY LOSS!
I have some Florida property you might be interested in. It is a little marshy, but one day it will be worth a fortune.

Seriously, I think that is bull. Every comparison I have seen shows stair interpolation with bicubic to be a little better than Genuine Fractals. Someone linked a long article about Sports Illustrated's image workflow. They have eleven pros in their New York offices whose job it is to perfect the images for publication. They have every big-buck program available plus state of the art Macs. They use SI for upsample rather than GF.

I use SI for upsamples I plan to print and it is just slightly better than using a straight bicubic or Lanczos filter. You can't upsample 110% without some loss – there is only photographic information for 100%. QImage has an upsample filter that is reported to be good, but I doubt it is magic either.

Cheap teleconverters aren't very good either. But high quality teleconverters will give you a real advantage in reach compared to using an upsample of a crop or using digital zoom.

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Old Jun 13, 2005, 1:11 PM   #6
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I have an older version of GF, and I find that plain photoshop CS doing several repeated 105% increases seems to do a better job.

Peter.
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Old Jun 13, 2005, 6:55 PM   #7
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I have an older version of GF, and I find that plain photoshop CS doing several repeated 105% increases seems to do a better job.
I was surprised that Sports Illustrated uses 110% steps for stair interpolation. I've compared them and 105% seems to be a tad better if you have plenty of RAM.

I have an action with four 105% increases and another action with four of the first action. I can get pretty close to what I am aiming for with the actions. I agree it is a little better than GF, but not by a lot. And GF isn't a lot better than a straight bicubic upsample.

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Old Jun 13, 2005, 7:01 PM   #8
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I use GF with Photoshop CS too & love it...especially when doing various image sizes for Web use, portfolio printing, etc. It's a pretty simple no brainer when it comes to saving large lossless files. For example, PShop(.psd) files that are 8mb can be saved with the same info by using GF(.stn) & they are only 3mb...a TIFF of the same image might be 16mb!

I'm sure if I was working for SI, I would use what they told me to use, but I'm very happy with the results GF provides.
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Old Jun 13, 2005, 8:37 PM   #9
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Is your version currentish?

The LizardTech guys probably have improved their code since I got my copy with an anceint scanner.
It is still a fair chunk of money to replace something that seems to work pretty good for free as an action in PS. :-)

Peter.
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