SX50: thoughts on digital zoom

Started Jun 17, 2013 | Discussions thread
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Don_Campbell
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SX50: thoughts on digital zoom
Jun 17, 2013

Digital zoom is a quick and handy way to get even more magnification that full optical zoom with these amazing cameras--that's an obvious "given." How much do you give up in IQ using digital zoom was a question that ran through my mind yesterday as I spent several hours watching big, beautiful birds sit still and do nothing more interesting than scratch their heads or ruffle their feathers--while I waited for interesting behavior.

I decided to to a test: take an image shot raw and then processed for a good final image, crop it and then upscale it 4x to compare with a full digital zoom image taken of the same scene at the same time of day, same exposure and same ISO.

Immediately there are all the quibbles anyone can dream up: how can you say that this is a fair comparison if you get to tweak it from the raw through the final JPG and the DZ photo doesn't get that treatment? Well, that's sort of the issue isn't it? When the camera does it the camera limits what you get by applying its algorithms not the ones available to me and my software. So--no comparison is "fair" by some measures but if the question is what is given up just accepting the DZ image it seems fair enough.

First: full digitial zoom to "200%" of the falcon of some of my other photos:

Digital zoom image.

Next, a raw file converted by dpp with slight contrast adjustment, then gently processed for a little more NR in raw therapee. That image was then cropped to 1000 x 750 px and upscaled to 4000x3000 using GIMP's sinc (Lanczos3) scaling and finally slight sharpening using GIMP's "smart sharpening" plugin. It sounds more complicated than it is in practice. It took about 2 minutes to get it to GIMP and another minute or two to crop, upscale and sharpen.

Upscaled image converted from raw and tweaked.

The answer (for me) is that yes, I can do better by performing my own "digital zoom" outside the camera. Alternatively, the camera's DZ image is pretty good and it's ready to go as soon as it is taken, which is a clear convenience.

There is one way that DZ is very much superior--it actually allows you to see in the viewfinder objects that are so far away that you can't really tell what is happening if you are not digitally zoomed. I've generally "looked" by taking a photo and then magnifying in the LCD display and DZ is way more convenient and faster than that.

Thanks for looking.

Don

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