Photography & exposure: Subject brightness range (SBR)

If there was no such thing as light, subjects would have no contrast. Light creates subject contrast which is obvious between the lightest and darkest parts of the subject.

If one subject was, lets say, an over-all neutral toned one, then it would have no contrast of its own. If that subject was lit by two lights with varying intensities, it would then have lighting contrast which would be evident in the difference between the brightly and dimly lit areas of that subject.

Playing with and/or incorporating different light sources with varying intensities would help you contract or expand the contrast range of your subject. If it was evenly lit, the only contrast range it would have would be that between the highest and the lowest reflectance parts of your subject. The greater the difference of brightness between different light sources, the greater the contrast will be.

The combination of the subject contrast and the lighting contrast defines the subject brightness range (SBR).

An 8-bit image file can theoretically accommodate an 8-stop difference scene range (256:1 difference between the lightest and the darkest part). A RAW file can theoretically accommodate up to 12 stops difference. As this is not always the case, it is always safer to assume a 7-stop difference for an 8-bit image, and an 11 stop difference for a RAW file image.

Why do we need to learn about subject brightness range?

Within one photographed scene, there are always different levels of brightness between different objects or between different parts of one object. An ideal scenario would be to be able to accommodate all brightness levels in one shot. Though this is not always, or even rarely, the case, being able to meter different parts of your scene and map those to the possible range your camera can capture can take you a long way.

Dynamic range is defined as the difference in light between the brightest value and the darkest value that the camera can capture. The human eye can see 24 different stops of light difference, taking into account the pupil dilation and contraction as a result of variation in light levels from highlights to shadows.

Cameras, however, only make instantaneous exposures, with film and expensive medium format digital cameras being able to capture 12 different stops of light variations, while most other digital cameras can only capture about 5 stops of light variations or even less.

Digital photography has made it easier nowadays for the photographer to capture his or her scene efficiently. The LCD display which shows blinking highlight areas when clipped, along with the histogram can help you determine if you have blown out any highlights or lost any image details on either side of the histogram.

A general rule photographers follow is making sure their image details only touches the left-most and the right-most points on a histogram. Going beyond the left-most hand-side of your histogram would mean that you’re losing shadow details of your image. Going beyond the right-most hand-side of your histogram would mean that you’re losing highlight details of your image.

If the scene or subject brightness range was not too wide, such as on foggy misty days, you would have enough room to manipulate image info distribution along the histogram. You can expose to the highlights, so that your image info is shifted all the way towards the right side of the histogram, without expanding beyond that. In such case, you can drag shadow details in post back to its appropriate position on the histogram so that they more occupy the left side towards the darks. You can also expose to the shadows without expanding beyond that. In such case, you can drag highlight details in post back to its appropriate position on the histogram so they more occupy the right side towards the lights.

Keep in mind though that exposing for your highlights is always better. Because if you do the opposite and then try to bring back your highlight details, your image would be prone to extra image noise especially apparent in the dark regions of your photograph.

A method that I always use in my photography to make sure I get the perfect exposure in every situation is using The Zone System.

The Zone System is a technique that was formulated by Ansel Adams and Fred Archer back in the 1930′s. It is an approach to a standardized way of working that guarantees a correct exposure in every situation, even in the trickiest lighting conditions such as back lighting, extreme difference between light and shadow areas of a scene, and many similar conditions that are most likely going to throw off your camera’s metering giving you a completely incorrect exposure.

I strongly urge you to read this article about the Zone System that I’ve written a while back for Phototuts+. The zone system works like a charm each and every time, 100% guaranteed, and in my personal humble opinion, it is something every photography (professional or not) should learn and get the grasp of before going any further with their photography.

Please do make sure you read this article, and comprehend everything it has to say. Here’s the link:

Understanding & Using Ansel Adam’s Zone System

And if you have any questions what so ever after you’ve finished reading, please ask them here in the comments below and I will be sure to answer them all.