Content-Aware Grain

Assuming one is trying to simulate film grain the S/W needs to account for some basic facts of where film grain arises and the fact that different film produces different grain profiles.  In B&W the developer also has an impact on the grain.  For example classic D76 contains "silver solvents" which smooth off the sharp edges of the grain while Rodinal has no silver solvents and the grain edges are sharp.  The reason why film developed in Rodinal appears to have more grain than D76.

Grain arises through the development process where in the exposed areas, the silver halides in the emulsion is converted to silver.  The higher the exposure the more silver (denser negative).  In the shadows there is little silver and the fixer removes the unexposed silver halide leaving only the transformed silver.  In the shadows there is little grain in film and in the highlights is where the grain appears. Grain depend on the emulation type.  Thick emulsion films like TriX will have contain bigger clumps of grain in a mix of sizes.  Think emulsion films (classic show films like Ilford Pan F) contains much smaller crystals in the emulsion so much smaller grain with no large clumps.  The Tabular grain films, Kodak T-max, Ilford Delta and Fuji Neopan, the silver halides are flatter and tabular. They tend to be finer grained but have less exposure and development latitude than the traditional grain films.

Film grain is just the opposite of digital noise since digital noise is higher in the shadows than the highlights.

For me the Nik collection provides the optimal tool for film simulations in among other things its ability to simulate realistic grain based on the film selected.  I find Silver Efex to be by far the best S/W for emulating classic and the newer B&W emulsions with a very realistic grain structure with the flexibility to tweak the grain structure to taste.  Granted I am partial to B&W but the few times I have used Analog Efex - it provides a comparable capability for color as Silver Efex does for B&W.