How do you distinguish film grain from digital artifacts on DVD? (1 Viewer)

[Dave H]

If I'm not mistaken, film grain is a bit "thicker" while artifacts blink more and are smaller. Or, is this even true? I'm curious to know the differences and wonder how reviewers know.

 

[Jeff D]

I'd say experience.

You should be able to see the difference. There are many factors for noticing this. The most important in the size of the viewing screen. On a small display you most likely won't see anything.

Film grain really looks like grains of say sand or something, they are random in posisition, but exist everywhere. If the film is grainy it will show through out.

If you know any photographers have them show you prints for slow speed and fast speed film. Fast speed film has larger grains and you'll be able to see them on a large enough print.

Digital artifacts are more random and infrequent. Although they exist everywhere. Encoding is done in a grid of squares 8x8 pixels, you may have seen this with a dirty disc or something. The probem may exist in one part of the frame and only that one block might have a problem.

Digital artifacts are very obvious in scenes with smoke or fog.

I'd sum it up as this... grain is constant and digital artifacts are random.

 

[Patrick McCart]

Pixelation (or digital artifacts) looks "squarish" and grain is globular.

 

[Mark Zimmer]

I'd dispute the notion that grain is constant. Film shot in lower light conditions will be grainier than that shot in higher light conditions. Different film stocks would probably be used in these circumstances. These different stocks could be cut together into the same movie, and thus leave you with some scenes that are grainy, but certainly not all of them, or differing levels of grain.

 

[Dave Koch]

I think a good, text-book example of film grain is the party scene at the top of Eyes Wide Shut.
dave

 

[Jeff Kleist]

A textbook of craptastic Super35 and moronic lighting designer induced grain will be the opening of the Harry Potter DVD

 

[Holadem]

I'd dispute the notion that grain is constant.

Mark, I believe they mean it for any given frame. Grain is consistent surface wise. Digital artefacts will appear at different (seemingly random) part of the picture.
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Holadem

 

[Jeff D]

I'd dispute the notion that grain is constant. Film shot in lower light conditions will be grainier than that shot in higher light conditions. Different film stocks would probably be used in these circumstances. These different stocks could be cut together into the same movie, and thus leave you with some scenes that are grainy, but certainly not all of them, or differing levels of grain.

Mark I think my point may not of been clear. All film has grain, that's what film is made of. There are many factors which cause the grain to be visible or not. There are fast and slow speed films with fine grain, but generally the higher the speed film, the larger the grain, you need larger grains, they are more sensitive to light.

What I ment by the constant was not throught out a film, but more a scene. If you have a 40 second clip and there is a constant grainy look that would be caused by the film stock.

Digital artifacts seem to come in an out and vary from frame to frame. This errors are a side effect of encoding. There are many different reasons for this too. MPEG is a delta compression with key frames. This means that the changes (delta) from frame A to frame B are what are kept track of, then a new frame is constructed from frame A plus the changes. If too much changes in a single frame the encoder much cut corners.

Bit rates limitations come from the encoder, decoder or DVD space or transfer from the DVD. This is by far the biggest culprit of the garbage. For example the Eagels Hell freezes over dvd which was shot on video had encoding problems. But, the reason is not because of the encoder. The problem is the audio. PCM data takes a lot of space becuase it isn't compressed (it's regular CD data). The space needed on the disc for PCM and DTS audio tracks left very little space for the video. The video suffered at the expense of great audio.