But zoom in to see the details, and it should be easy to tell which one is which:
Zoom in to see the real picture
Most photos with even a moderate amount of noise look just fine on a computer screen or when printed at a small size.
The threat of noise shouldn't scare you away from raising the ISO setting on your camera when you need to; when you're done, though, you should make a point of lowering the ISO to the camera's lowest setting. Most photos with even a moderate amount of noise look just fine on a computer screen or when printed at small size; noise becomes noticeable only when you make large prints or crop a photo to show smaller details.
In any event, the average camera's noise performance has improved dramatically in the past few years, enabling you to shoot at previously unheard-of, crazy-high ISOs and still get very usable photos. Some cameras today go as high as ISO 12800--seven stops faster than ISO 100, and strictly the stuff of science fiction as recently as a decade ago.
Not only will you get more noise in high-ISO photos, but you'll get more noise in low-light photos, such as those taken indoors or with long exposures at night.
If you're shooting at higher ISOs and you save your photos in JPG format (rather than in your camera's Raw mode), make sure that your camera's noise reduction feature is turned on. Your camera runs a basic noise-reduction filter on your photos to get rid of the worst of the noise when it saves them initially. Some cameras have a more thorough noise-reduction filter specifically for higher ISOs; check your camera's user guide to see whether yours does.
Software after the fact
If you're willing to do a little extra work, I highly recommend running a noise reduction filter on your computer. You can find noise removal filters for your favorite photo editor, for example, or you can try a stand-alone program. Noiseware Community Edition, for example, is a free noise-removal program for Windows (the full version by Imagenomic for both Mac and Windows costs $80). ND Noise, a Java-based application, is available cross-platform. If you're serious about fighting image noise, also check out Nik's Dfine or Neat Image for Mac and Windows. Many of these programs come as stand-alone packages and as plug-ins for software such as Adobe Photoshop, Lightroom, and Apple Aperture.
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