Cropping And Noise

Can cropping too much create noise in a photo, and if so, what is going on to cause that to happen.

A couple of weeks ago I took a picture of a Grey Catbird with my 5D, ISO 400. I used a flash, and as far as I could tell the exposure was okay. The only PP I did was to crop (and I can't remember how much) a bit of curve work, and some minimal sharpening.

Here's the EXIF data: f/6.3, 1/400, ISO 400, focal length 400mm, Flash - fired.

I'm sure the result of the noise is something I'm doing, but I don't know what it may be.

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It was either flash or that minimal sharpening...Not sure :P.

No, it looks as if you underexposed (easily done with that dark subject). Did you have to boost the darker tones with curves? That would have done it. Cropping can't by itself introduce noise although obviously it will apparently reduce resolution if you then enlarge to the same size. But if you shot as jpeg then cropped and resaved as a jpeg, that could introduce compression artefacts (although what you have here looks like sensor noise).

I don't know whether you shoot RAW or not - if not I would recommend it.

You can "rescue" this very nice shot using Noiseware or a similar plug-in. Here is the result of the auto settings on your jpeg:

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Although Canon's CMOS sensor are exceptional in high ISO noise performance any type of heavyish cropping will magnify said noise, especially ISOs 400 and up. Sharpening can also add to that noise if it was already present.