Tutorial: adding grain to b&w

There are of course several ways to approach the subject of added grain. I'm talking about adding noise to an image that looks more like film grain and less like digital noise. So basically, we are simulating film grain. The distinction that I'd like to make between the two is that

1) Digital noise produced in-camera rarely looks pleasing to the eye and it is not "random" in the way that the eye easily accepts. It is an annatural pattern created by various factors, but usually the excessive noise is due to increasing the sensitivity (ISO) of the sensor in the digital camera.

2)In film-like noise, the pattern of the noise can be made more natural looking (softer and more random for a start) - i.e. something that's not as "harsh" and doesn't immediately look like it doesn't belong to the image.

There's some noise generators built into most post processing programs, but the effect they produce doesn't look very much like the effect we are going for here. You might want to add grain for several reasons.

Why add noise?
One reason for added noise/grain is to create a certain mood to the image. But added noise is also good for adding texture to an image. This may sound weird, but sometimes if you have an image (especially from a digicam) and it suffers from excessive noise reduction, it may look better and more natural if you ADD noise in one of the following ways. The image's noise reduction could be due to heavy in-camera noise reduction or noise reduction done in post processing to a high-ISO image. In either case, the idea is to add some texture back to the image so that it does not look too flat. The main disadvantage of noise reduction is, that it tends to remove details and natural texture from an image and leaves the image looking "flat" and unnatural - with areas that are too smooth.

You might want to take look at this good primer to b&w pics by Petteri sulonen:
http://www.prime-junta.net/pont/How_to/n_Digital_BW/a_Digital_Black_and_White.html
the part about grain begins here:
http://www.prime-junta.net/pont/How_to/n_Digital_BW/a_Digital_Black_and_White.html?page=5

Now, how to add grain step by step. Method #1.

1a) One of the ways is to make a white layer and add noise trough filter -> noise -> add noise (amount ~4.0) and then blur it with gaussian blur amount ~ 0.2- 0.5. Then INVERT the layer and change blending mode to screen and expriment with different opacities. You can make several such layers with different amounts of blur and different opacities and you can duplicate the layers to make the effect more intense. You can also resize the grain layers to affect the appearance of noise and size of the particles.

Some other blending modes like ´linear dodge´ work too.

1b) part two of the first way:
make additional layers but do NOT invert them
DO change the blending mode to multiply.
These levels must not have the same grain pattern as some of the ´screen´ noise layeres, or they will cancel each other out...

Some other blending modes like ´darken´ work too. And you can experiment with levels, curves, etc to change the appearance of the noise layers.

2) Then there is of course the way explained by Petteri - scanning slides for noise, which may be a bit of work but gives good results.

3) Third way, "from the can" solution (and a horribly expensive one) is using the Photoshop plugin ´Grain Surgery´ http://www.visinf.com/