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I own a 10.2MP Sony A230, and I like to take it with me to important family and friends events...

I rarely print my photos, and even then never more than around A4 size, they generally end up on facebook or zipped up and sent to whomever asks to see them. I was wondering whether it would be worth it to downscale these 10MP images, for the sake of image quality, to something around 6MP... and, if so, should I simply set my DSLR to take photos at a lower resolution or take them at 10MP and then downscale afterwards using some PC software?

Also, given the effects oversampling can have on noise (or, at least the effects I have been led to understand it has) would this allow me to get better quality images in low light using higher ISOs?

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Keep your photos in 10MP, you can always downsample them later, but you can't effectively upsample them again if you do decide you want to make a large print. Likewise leave your camera set it it's maximum resolution.

Downsampling does indeed reduce per pixel noise, but then when comparing at the same output size, all you've effectively done is reduce the amplitude of the noise but increased it's coarseness. I always prefer more finer grained noise. Plus when you upload them to facebook they get downsampled anyway.

The short answer being there's very little to be gained by reducing the size of your photos. If you're really concerned about noise, invest in a good piece of noise reduction software.

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    \$\begingroup\$ re: the downsampling done by facebook and similar apps. I've noticed that if I do the downsampling to my own images before uploading them to facebook I seem to get better results in terms of tonal gradation, especially with deep shadows, dark skys, etc. \$\endgroup\$
    – Michael C
    Aug 16, 2013 at 6:07
  • \$\begingroup\$ I have accepted this answer because it was first, and it was helpful. Though that is not to say that AJ Henderson's answer wasn't helpful too, it was just later. Thanks to you both. And thanks, Michael for the suggestion of down-scaling before uploading. \$\endgroup\$
    – Luke
    Aug 19, 2013 at 11:25
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You can still shoot at full quality and then apply it later. The gain is because of averaging. If one pixel happens to be hot then the next one may be cold. When you average them, you get something that is smoother and should minimize the noise in theory. It does make an impact on low light performance, which can be seen with the way HTC recently did their "UltraPixels" which are really just applying this principal to the images that it captures.

If you are shooting to JPEG, then a little bit might be lost, but if you can shoot to RAW at full quality, then there isn't any reason not to just do it after the fact if you need to.

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