You noticed a bear inside a cave just before evening. You recall seeing a duplicate of this shot in the last National Geographic magazine. You bring your thousand dollar camera up with a proud telephoto lens sticking out a couple feet and set ISO to 200 only to find shutter speed showing 4 seconds. Okay, no problem, Set ISO to 800. Still a shutter speed of 1 second. But the bear is licking its belly. Stock photo sites usually don't tolerate tongue blurs. No worries. ISO 25600. Now you got a shutter speed of 1/32. Okay, manageable. So you shot away 20 continuous shots and got 2 or 3 sharp enough. Happy ending for most newbies, especially those with cameras boasting sensitivities up to ISO 25600.
Then comes the clutching your hair and moaning when you start up Photoshop and hit "100% view".
Then the optimist grasps the reign again and you apply a noise reduction. Nothing significant. Maybe apply it twice?
After 4 cycles, there is no noise. But there is no hair on the bear either.
So what went wrong? What can you do in such hopeless situations?
Noise reduction has a separate workflow in shots with excess noise:
Smarter post processing: Decide the severity of noise. If it is intense and unbearable, do NOT process the RAW for noise. If you have Canon's DPP for RAW processing, turn the noise reduction OFF. Transfer the file to a 16-bit TIFF. Open in Photoshop.
I guess you know about the method of removing chromatic aberrations using a blurred layer set to color mode and then using mask? Do the same thing but use the brush to remove noise in noisier parts like sky or dark parts. This is very effective and efficient in removing chroma noise. You can merge the layers and redo this any number of times without affecting the main colors of the image and without softening the image at all. Better method of chroma noise removal than most commercial software including Topaz and Noise Ninja.
Next the grainy part of noise. For this, use whatever noise reduction software you use. Then read below about reducing the image size. It is a MUST step for severe noise shots, otherwise you get artifacts on your image. You can also try resizing the image first and applying noise reduction later. Usually works better for some images.
If you didn't have excessive noise, you can just use the RAW processing software's noise reduction tools. I suggest you use the original camera manufacturer's software for initial RAW processing instead of Photoshop or third party software. Believe me, the camera makers understand their cameras best.
After this noise removal with the RAW processor, make a TIFF out of the file and resize it to something smaller. Keep it random. Example, reduce a 1000X500 file to 259X129, not 500X250 or 750X375. That reduces noise noise grains slightly better. And use the Bicubic smoother etc. Never use bicubic sharper for images with high noise levels.
Smarter shooting: Understand your camera and how it works. First thing you should understand is that noise is directly caused by sensor's internal heat and ISO sensitivity. If you are shooting a photo at ISO 12800, it would be better to make sure your camera is cool. Don't use ISO 12800 after an hour of live view shooting. It makes things worse, even if slightly.
Second thing, the ISO. Keep it low, whatever happens. You need a higher shutter speed? Then use Aperture priority mode and use the widest aperture (smallest f-number). If you still don't get enough shutter speed, do NOT increase the ISO. Better to just decrease the EV to -2 or sometimes even -3. That would give you a higher shutter speed. And when you increase exposure of images in post processing, you'd still have low noise compared to the same shot captured with extremely high ISO and EV 0.
Look at your subject carefully, if there are no risks of overexposing and your subject has no white areas, you can reduce noise with another smart move. Suppose you can afford a slightly slower shutter speed and you are shooting at moderate ISO like 800 or 1600, then you should set EV to +1/3 or 2/3...whatever you can use without blowing the highlights. That reduces the noise to signal ratio and you get lower noise.
These methods can help you out in helpless situations that you may encounter when you are not ready or when the use of flash is not allowed, like in caves with archaeological artifacts or during wildlife photography at sunset or sunrise.
Below are some shots that looked attractive and were shot using these techniques. (please ignore the shooting parameters shown by DT. They are random values in most cases)