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Graininess

Published : 7th July 2004


Okay - correct me if I'm wrong, and don't be afraid to use sarcasm:

The reason we see more grain in underexposed negatives is that the ratio of density to clear negative is much lower, so when we print at a lower printer light to make the highlights and mid-tones look proper more light passes through the clear, or "black" parts of the negative where only the largest grains are exposed (if at all), making the shadows appear grainy and gray, or "less black."

This is in contrast to a thicker negative where the ratio between density and clear film is greater, so when we print for the highlights and mid-tones the dark shadows are well down below the threshold of where the print film will see the grain, resulting in deep blacks.

Art Adams, DP [film|hdtv|sdtv]
Mountain View, California - "Silicon Valley"
http://www.artadams.net/



The thinnest parts of the negative are the grainiest (because they represent the shadows, where there was only enough light to expose the bigger, faster grains). Where there is more exposure, the smaller grains come into action as well, filling the gaps, reducing the graininess. By a very simple piece of logic, if you reduce the overall exposure, the entire frame will have fewer of the small, low-speed grains exposed, hereby increasing the average graininess over the whole image.

But that's not all.

When you print a well-exposed negative, those thinnest areas print to a good dark black. An underexposed negative must be printed at a lower printer light, with the result that the shadow areas, (now further down the negative characteristic curve, onto the toe) don't print to black, but a muddy grey. Now it turns out that we perceive graininess more in proportion to luminance: the brighter an area is, the grainier it seems (all other things being equal). So muddy greys _look_ grainier than equally grainy blacks.

And wait, there's more.

Psychologically, the eye looks for strong patterns. Strong deep blacks, and bright highlights (even a well-placed rim light) satisfy this need. In the absence of this (e.g. in flat, underexposed scenes) we settle for the next strongest pattern, which is often the grain structure.

And just for a sting in the tail . . . don't forget that when you look at a print from a negative, what you are seeing is not the grains, but the spaces in between the grains. In fact, the grain structure that you see is not due to individual grains, but the "clumpiness' due to the randomly distributed nature of the grain pattern.

You can see my attempt to illustrate that on page 63 of my book (it helps if you view the book about 2 arms-lengths away or put it on the floor!).

Dominic Case
Atlab Australia



> The thinnest parts of the negative are the grainiest

But isn't the opposite true for B&W negative?

Jeff Kreines



Jeff wrote :

>The thinnest parts of the negative are the grainiest. But isn't the >opposite true for B&W negative?

Several things are different about b/w negative.

Infectious development is one factor that might come into play. The fact that (afaik) there is only one emulsion layer of mixed grain sizes, rather than the mulitlayer approach of colour stocks (fast and slow layers for each colour) is another.

And it's certainly true that reversal emulsions work the opposite way. With reversal, the big grains are the ones that are exposed and therefore developed in the shadows, so that when the image is bleached and redeveloped, it's the smaller grains that are left over. Hence smaller grains in the shadows, larger ones in the highlights.

Dominic Case
Atlab Australia



>Hope that's clear and not too grainy.

Next time write more words and then we can pare it down to the important stuff. If you write less then I have to think harder and that's when the grain appears.

I think of this stuff fairly intuitively, and yes, now I get what you're describing. Thanks for making it make sense. I always knew the "thicker negative the better" process worked but not specifically how.

There's a reason I got "D's" in math and physics and "A's" in English and art.

Art Adams, DP [film|hdtv|sdtv]
Mountain View, California - "Silicon Valley"



>Okay- correct me if I'm wrong, and don't be afraid to use sarcasm :

What should I do if you're right? Say nothing?

In intent I think you're right. In the first part you mean to say "when we print at a lower light . . . .LESS* light passes through the clear parts of the negative where only the largest grains are exposed . . .making the shadows appear grainy and gray . . ."

*not MORE.

Hope that's clear and not too grainy.

Dominic Case
Atlab Australia