Sunday, January 13, 2013

An 18% Grey World

18% Grey Card
18% Grey Card
Or why auto settings kill your photography.

Camera technology has come a long way over the decades, shutter speeds have gotten faster and more precise, films more sensitive, the advent of digital and so on. One aspect really has not changed much in the past fifty years - and it's a big one, that is the expectation of 18% grey. As smart as cameras have become there are two very important things that they are missing, an understanding of what your subject is, and more importantly how you want to portray your subject.

So what is 18% grey, where did it come from, and why does it matter. If you take a sample of 10,000 8x10s from ten thousand photographers (proffesional, hobbyist, neophyte, or otherwise) randomly select one square inch out of each photo and blend it all together you will get an average that is 18% grey. That average is why light meters whether in the camera or separate are calibrated to 18% grey. That expectation is what your camera uses to determine exposure, color temperature, and tint. Occasionally 18% grey is rightish, most of the time it is wrong.

Lets start with an example of where that expectation is rightish, landscapes. Landscapes are lit by a giant light source, the sun. Because of this they tend to be lit very evenly, making exposure throughout the frame more consistent, though in many cases the sky will be too bright compared to the land, hampering your camera's grey interpretation. Another issue, for example, your subject may be very green (trees, grass and such) effecting your cameras interpretation of tint, or very yellow like sand confusing the cameras color temperature. So while most all cameras do an ok job with landscapes, you have probably taken pictures of breathtaking scenes only to be disappointed with what the camera rendered. This can be particularly true with sunsets, the world on average is not as red as it is at sunset, so the camera will shift the tint towards green, and the world is not that yellow, so the camera will shift the color temperature towards the blues. It will also likely bleach out the color of the sky trying to properly expose the land, or may leave the land crushed by shadow as it exposes for the sky.

Because of these kinds of limitations camera manufacturers have started adding a broader range of auto functions to the camera, they may call them "scenes" or "styles". These give the camera a closer idea of what lays beyond the lens. So for a sunset you can set the camera settings to "sunset". This gets the rightish interpretation of 18% grey closer, but a sunset over a snow scape is still considerably different from one over rainforest, or one over the dessert.

So lets look at something that grey expectation gets very wrong, wedding photos. Particularly photos of brides in front of white backgrounds (high key) or tuxedos in front of dark backgrounds (low key). In both cases theses subjects fall outside of 18% grey (mid tones) the camera expects. Brides in front of white will come out dingy as the camera underexposes the image to push a very bright subject into an 18% grey world. It also does this to snowscapes and other high key subjects. The opposite happens to tuxedos, the camera overexposes them, again forcing them towards 18% grey. 

Once you understand what the camera is getting wrong you can then start to adjust your settings to get the images you want. If we go back to the example of the bride in front of a white wall and understand that what the camera is doing is under exposing that image, you can then correct it by upping the exposure. Or if your camera has a snowscape setting you should understand that you can us that as an approximation for any high key (mostly white) subject. You may find the snowscape setting better for white sand beaches then the beach setting which is expecting yellows and browns to make up the sand, likewise the beach setting is likely to fail on volcanic beaches where the sand is black.

Another area the cameras auto setting fails is action. This is an easier correction as the  "sports" setting will favor a fast shutter allowing you to freeze action. In general when the camera gets its meter reading it will set a shutter speed close to 1/60th of a second. This is the slowest shutter you can reasonably expect to hand hold the camera. It will actually be much higher, perhaps 1/120th if you are zoomed in on something. The camera will favor slower shutter speeds so it can close the aperture as far as possible to still get proper exposure while giving you the deepest depth of field on the lower ISO settings. The logic being if you can hand hold the camera with a low ISO and large depth of field it will give you properly exposed photos for the widest range of subjects while limiting noise (and creativity). I will discuss how shutter speed and aperture effect photos in much greater detail later, but it is important to understand how the 18% grey expectation effects the camera's prioritization of these settings. 

Looking at all of the things effected by the 18% expectation of the camera may seem quite daunting, it reaches into everything the camera does, understand that. But then break it into digestible pieces. Start with the ones that have the greatest effect on your photography and work out from there. Having this understanding of where the cameras expectations come from will let you correct for what you subject is and will immediately improve your shooting.

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