Noise/Grain

[x264]

How do i differentiate between grain and noise?
Is this grain or noise?

[hech54]

Just buy the Blu Ray.
http://www.blu-ray.com/movies/The-Terminator-Blu-ray/61372/

[sanlyn]

Grain is noise.

[jagabo]

If it's from film it's grain (actual grains of silver iodide). If it's from video it's noise.

[sanlyn]

True. If you go to a movie theater and watch a real movie ( a movie made with film cameras, not with video gear), the natural grain of film is evident. However, transferring film to analog media (tape) or digital media can add digital noise effects to the effects of film grain. From the still image you posted, the soft-grained effect appears to have been part of the film, and sometimes movie directors will process film in such a way as to exaggerate or even change the character of film grain. Encoding that grain effect into digital form adds digital effects in the form of chroma noise. How much of those two effects (film + added digital grain or random chroma noise) are in the image posted would be difficult to say. But some of it is there to prevent banding while encoding. If you remove all of the tiny specs 100%, several things will happen:

a) A lot of fine, soft detail will disappear or turn to mush. The image will begin to look plastic.
b) Barroom smoke or haze effect will dissipate, which might not be what the movie's producer wanted.
c) Color banding and block noise will appear rather than smooth color transitions, especially in large areas with little or no hard detail. This is partly due to the inability of digital encoding to maintain clarity in dim, low-acutance areas without taking special measures during the encoding process;and because fine color gradations usually require a greater range and variety of hues between areas of gradual color transition, and the range of hues in film surpasses that of video. This includes black-and-white.

This article on digital noise gives a few samples: http://www.cambridgeincolour.com/tutorials/image-noise.htm