Tutorials
Reducing noise
Noise levels depend on one side on your camera and the other on how you use it. The most important thing to minimizing noise is making correct exposures. Make sure your subject is well lit, and that you are shooting at the lowest ISO possible. Generally noise is more visible in shadows and areas with little texture. Out of focus areas are especially good at revealing noise. If you do did take an otherwise stunning photo which suffers from noise, then either put it in the trash or try to fix it.
How I do it:
- Duplicate the image layer
- Reduce the noise on the new layer
- Mask out the parts which should have maximum sharpness and detail
Lets get started!
Figure 1
For this tutorial I will use this image of a card house. It's no masterpiece but will do for the purpose of this tutorial.
Figure 2
As you can see it has some bad noise in the shadows.
Figure 3
Duplicate the layer. On this new layer reduce the noise. If you have Photoshop CS2 or later there is a filter called Reduce Noise, which you'll find in the menu Filters>Noise>Reduce Noise. It works okay, if you can also use software like NeatImage or NoiseNinja to do this. Use as high value you have to to get rid of the noise. The image can become a bit muddy and soft in places but dont worry about that now. If needed, use the blur tool 
on out of focus areas where noise is the most visible because you have no texture to hide it. Watch the edges near the subject or you might get an ulgy glow.
If you don't have this filter you can use gaussian blur on a low radius setting, or preferably use the blur tool manually.
Figure 4
Now you should have no noise in the picture, but its soft and might have lost some of it color because of the Reduce Noise filter. We need to mask the top layer to bring out the sharp, low noise areas from our original image.
Figure 5
Make a layer mask by clicking the rectangle with a circle in it in the layers palette.
Figure 6
Start bringing back the first layer by painting with black on the layer mask. This takes some technique and can be done in other ways such as channel masks, but thats not in the scope of this tutorial. Paint with black on all bright noiseless areas. You can always use white to bring back the top layer. On straight lines such as the cards you can click once with the brush, then hold shift and click again to paint a straight line, it can be very handy. You can see the layer mask by holding Alt/Option and clicking the layer mask in the layers palette. (that's what I've done in Figure 6 to show you my mask)
Look at the iamge at 100% to make sure there is no noise in the image. If there is noise paint with a white brush on low opacity on the layer mask to get rid of it.
Figure 7
Here I have made the mask a quickmask just to show you what it looks like and what areas are from the original image.
Thank you for reading this tutorial, hope you learned something!
Roll over the image to see the original
Coming soon:
Isolating with the pen tool
Isolating with channel masks
Correcting white balance
Correcting purple fringing