Photography question

To: "Birding-aus" <>
Subject: Photography question
From: "Peter Shute (NUW)" <>
Date: Thu, 21 Sep 2006 10:31:39 +1000
On Wednesday, September 20, 2006 9:52 PM Terry Bishop wrote:

Also use the least
digital zoom as possible.

That's the advice I always hear, but is it strictly true? Most people seem to be of the opinion that if you're going to digitally enlarge a photo, then it's better to do it with the more powerful software available on your computer.

I have a theory that this may not be true if your camera can only save photos as jpg's. These are compressed and some information has been lost from the image that was captured. So enlarging the compressed image later may not give as good a result as allowing the camera to do the same operation on the raw image before compressing it, if it does indeed do it that way.

My camera (Canon Powershot A40) appears to do the digital zoom operation using the raw image before saving it as a jpg. I've proven it to myself by taking a photo of a newspaper at a distance where the writing was barely legible on the final image. Taking another photo from twice as far, but with 2x digital zoom, resulted in an image that was noticeably easier to read. I've never actually tested it on a real subject, bird or otherwise, because they tend to move while you're moving back for the digital zoom shot, and the differences can be too subtle to allow you to decide which image is better anyway.

I guess it depends on your camera. If it can save raw images, then it seems it would be better to enlarge them later. If it only saves jpg's then it depends whether its digital zoom enlarges them before or after compressing. I suspect they probably all do it before, but you'd want to do the same test I did before trusting it.

It could also depend on the quality of the algorithm used for the digital zoom. A camera with a slow processor may use a quicker, low quality algorithm, negating the advantages of enlarging before compressing. But then again, such a camera may also have a low quality compression algorithm, making the digital zoom advantageous. There are no standards for jpg compression: what some cameras do with what they call "super fine" may lose a lot more information than another camera's ""fine" mode.

Summary: Using digital zoom *can* be better than enlarging later with software, but you'll have to test it with your camera to be sure.

It goes without saying that setting the camera to the highest resolution and best quality compression can only help too.

Peter Shute

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