Photographic gear, of course ;)
Maybe the professional doesn't need to worry that much about grain/noise. Modern and professional (expensive) cameras create noise free images on most situations ...
But I do worry about it, I can't afford top quality hardware so I have to work with what I have. Especially for those others facing this kind of issue, I decided to share some tips and tricks.
If you decide you absolutely need to reduce noise of a particular difficult image, go for it, Neat Image or Ninja Noise are/were great for that. But remember that there is visual information on grain/noise. It is a kind of chemical/electronic mechanism that overimposes on the image, but does not erase it, just makes it less clean. So, if you reduce grain/noise you'll also reduce visual info and you'll loose detail.
Learn to use those tools ... that is not what I want to talk about. I want to share some dirty tricks :)
I'll stick to the word noise from now on.
My camera's sensor is really noisy, darks are awfull. Cameras produce more noise under low light situations or in underexposed images, it's a natural thing of the digital world, there will always be noise and when you have less light you have less "signal" and the ratio between signal and noise will decrease creating noisy images.
This is why it's generally better to overexpose, just be carefull not to blow those highlights, but keeping the histogram balanced to the right side is a good thing.
Point 1: Working against noise begins when shooting!
Now, if you have large homogeneous areas on your images that is mostly where the noise will standout. That could be a huge blue sky, the dark night sky, or even large unfocused areas around your subject. (If you are into macro photography like I do you'll have lots of this) Those are the places where noise reduction has more impact. And those are also the places where there's little or no visual information, hence, in theory, you can apply all the noise reduction you want because there's no detail to loose! But software I know of don't have this option or don't do it right. (This is also an hint to software image programmers ;) )
Starting from here, always assuming photoshop use, we can just select those areas and reduce noise only inside the selection.
Hint: skies are usually very easy to select using the magic wand tool. Woopps, watch out for those clouds, you can't select them!
It's just a starting point, but not that good. Exact selection may be hard to get and hard selection edges will show a noticeable difference in image texture that might ruin the picture. We can "feather" the selection but just that will result in some detail lost (noise reduction) out of the kill (noise) zone. Contract your selection a bit before feathering. Values I might use, contract by 10 and feather by 5. If you magnify the image to 200% or 300% you'll notice the gradient of noise reduction around the selection, but being close to edges where you have details with lots of visual information it's perfectly negligible. Probably dificult to see, even if you're looking for it, at 100%.
Another issue that relates to what comes next, the out of focus areas. Some lenses' optics just create ugly out of focus details. They can turn white (out of focus) lines or bright spots into double "blurs" making this part of the image look fuzzy, sometimes like if your hand was not steady, just for the out of focus!
Reducing noise won't help much here, but the blur tool will! Remember? You have almost no details here, why not blur? In fact I found that blur is sometimes a better noise reduction tool than noise reduction itself! Noise reduction sometimes creates, not so random to the eye, patches of, previously more less random "uncleaness". Blur cleans that all away!
Wait, don't go blurring everything away just yet! Even inside a selection you'll always "blur" some details out of the selection into it! If you blur too much or around hard edges you'll create halos. Same as before aplies, contrat selection, feather and blur just a little, then contract more and blur a little more, and again ... and it should be enough. A clean, halo free, image, well not always, but things are definitely looking better. Gaussian blur values I use are between 1 and 3, very small amounts.
Now try this do both things, noise reduction and then blur! Select, contract, feather, reduce noise then blur (maybe contrating your selection a little bit more before). You'll need to use smaller amounts of noise reduction and smaller amounts of blur, and the image looks more natural. As a side note, don't overdo any of these things or will get washed out backgrounds and out of focus areas, not at all natural!
Another Blur problem might be banding! If you're working on a very neutral area, or using mostly only one the color channels, you might start seeing some banding! Blue skies easily create this if you overdo your blurring. If you can't avoid this effect in any other way, don't worry, just add some noise!
Yeap, after using blur to reduce noise, add some noise to create a kind of dithering effect and eliminate banding! But this is a different noise, it's photoshop created, very fine and smooth noise. I use gaussian noise values from 0.1 to 0.6. You might have to type those 'cause the slider won't get to these so small values. Also try the other options of this tool, some are better for this situation and some for that. Sometimes it looks like magic, your skies loose the banding effect and become more natural!
A little back now, about making selections.
Generally I use the line selection tool. There's no need to be very precise, just draw your selection a few pixels inside of the noise reduction area (you won't need to contract later) and then feather it.
Now imagine you have an image where the size of out of focus is realy large, but divided into thousands of little areas! Like a plant isolated with DOF against an bunch of other plants. The selection process might be a nightmare!
You can go one of several ways:
Do all your other processing on the image, create a Snapshot on your history folder, use whatever noise reduction technique you want all over, and then use the history brush tool (with a soft brush) to paint your original detail back into the picture.
Duplicate your layer, hide the one above and apply noise reduction on the other (I'll call it background). Make the first one visible again and apply a hide all
layer mask. Then select the mask, a soft brush, and paint this untoutched layer back again on top of the background.
You can also put the "original" on top and kill the noise out of the other layer. Mask the original with a show all
layer and paint, in the right places of the mask, black holes to show the noise free version below.
I prefer one of these last ones because: I can easily revert any actions, I can paint any level of grey to mix the noise free and original layers. I can even dessaturate or darken/lighten a little the background to smooth a too much cluttered back scene or to make the subject really stand out! (realy dirty trick!!)
When everything is ready, convert to 8 bits (I have been always working with 16 bits images), maybe sharpen a little and ... noise is back! Carefull with that sharpening! If you realy need it, set the threshold value to a little more than default (I use values around 1) and noise won't be back so easily. There are lots of other ways, but this is the simplest way I know of sharpening noise free!
Other things you can do with this tips ... try using the select and blur things selectively on your pictures ... for instance on a landscape select mountains further away and blur them just a little bit! Wow ... that might be a wonderful way of creating great depth in our images! :)
Sorry for so much text ... go on, have fun :)