When shooting slide film, many photographers intentionally under-expose by around 1/3 f-stop in order to saturate colours and prevent highlights blowing. Slide film is extremely unforgiving of inaccurate exposure and a 1/3 of a stop latitude is about all you will get before your slide ends up in the bin.

Digital is much more forgiving in this respect and over/under exposed images can be rescued to a surprising degree - particularly if you shoot in RAW. This aspect of digital photography differs radically from film camera technique, so in this tutorial we will explore how to get the very best out of our exposure settings when shooting digital.

So why not under-expose everything on purpose in digital? The answer is that we don't want to expose noise (the digital equivalent of film grain ) in the dark areas of our image (particularly if using high ISO settings on the camera) when we come to adjust the levels in post processing on the computer.

With digital it is often better to lean a little more towards over-exposure (within reason) and adjust the highlights back down again later in the RAW conversion process (or in "Levels" if you are still shooting jpegs). You can see the effect of opening up the shadows and exposing ugly noise in the background of this under-exposed image of a nuthatch.

Now, I am not suggesting that you just start over-exposing images intentionally all the time to reduce noise, as there is a tightrope to walk between either clipping important highlight detail and exposing noise - so do try what I am about to suggest, but don't overdo it !

Check your camera's histogram

When you take a test image of a subject to check exposure on the back of your camera, switch to the histogram mode (often called info or something similar) and look at the graph. If there is any gap between the right of the graph and the right hand edge of the box, retake the image after adding more positive exposure compensation - that is dial in +1/3 or +2/3 etc until your graph is pushed to the right as far as you dare go without blowing critical highlights.

This method is known by some digital photographers as "exposing to the right" - in other words applying a little more exposure than the histogram suggests to push the pixels further to the right in the graph.

As you close the midtone slider back down in the RAW converter or in Levels, the noise remains wonderfully concealed. This is yet another reason why shooting RAW is hugely beneficial over shooting jpegs. There is a surprisingly large latitude for highlight and shadow retrieval from the original RAW image - far greater than trying to do it in levels later. Just don't push your luck too far - or you will irretrievably loose your highlight detail - even RAW has it's limits !

The technique of "exposing to the right" works best when your image has a lot of midtone and shadow detail (where noise can lurk) and not too many highlights that are critical to the image within it. An example of non-important highlights could be specular highlights - such as those that you would get from flecks of sunlight on water. You will probably not be too upset if these go to pure white.An example of critical highlights could be feather detail in a white bird.

The white bird is a big test of exposing to the right, so in case you are skeptical , let me put my money where my mouth is and have a go.....

Lets look at an example.

Here is a white dove on a dark fence rail. From the histogram in the Photoshop CS2 RAW converter you can see that the image excedes the dynamic range of the camera - as both the shadow and highlights are clipped. If the bird was surrounded by foliage and other midtones, I would probably have elected to have under-exposed the image by a further 1/3 stop to guarantee not loosing highlight detail in the feathers. However, in this image, there are a lot of dark tones in the fence rail too, and if I under-exposed the image any more, I would expose noise in the shadows and midtones as I re-adjust the Exposure and Shadow sliders back up again in the RAW converter.

Little known facts

It is a little known fact that camera histograms do not show you the actual RAW image in the preview screen on the back of the camera. What you are looking at is a tiny, embeded jpeg of the same image.This has been converted from the unreadable RAW file to the jpeg using the camera's chosen approximate parameter settings. can you see what am getting at here - the camera may not have got it right, and there may be more highlight information available beyond the end of the graph !

Also, the camera manufacturers usually set the histogram to display very conservatively at the highlight end - so you can usually push the highlights a bit more than the camera histogram is suggesting and still get away with it. Use this information to your advantage - but don't blame me if you overcook it !

Before we go on, go back and just take a look at the histogram of the dove in the above image again and you will see that the very brightest highlights have just blown on the extreme right of the graph (sharp narrow peak circled in red). Also look at the bird's breast feathers - they look a bit blown don't they ? Has this guy gone mad ? ....Please just bear with me for one more moment........

The next step

The next step is to adjust the exposure and shadows sliders to pull the graph back into the frame of the histogram box at each end. Look at the red circled areas of the graph - See that the image no longer looks clipped at either end ? If you hold down the Alt key as you adjust the exposure slider you can actually see at what point the highlights just start to clip. This is the setting to adopt. If the image looks a bit dull in the midtones, you can now brighten it up again with the brightness slider.

So has it worked ?

I clicked Open to open the image in Photoshop, and then selected Image>image adjustments>levels. Now lets take a look at what we have got ....

I have set view to 100% (i.e. "Actual pixels" as you always should to view critically) and sharpened the image a little in unsharp mask. Now, first look at that levels histogram - it looks perfect ! Now look at the breast feathers of the dove - do they look over-exposed to you ? No - me neither. Finally - look at the background - grainless !

This is a great example of "exposing to the right" in action. It can be extremely effective - I use it often and whenever I can if the conditions appear right to benefit from it. But as I said before, and I will say it again, although there is a surprisingly large latitude for "correcting" images in the RAW converter don't overdo it, or you will irretrievably lose important highlight detail. If in doubt, and if your subject gives you the time to do it, bracket the exposure of your images just to be safe.

Limitations

The shovellers below were taken on a sunny day - when the contrast was very high. This situation is a nightmare to expose correctly - they and the water are predominantly midtones and shadows - but those white feathers will easily clip to the point that they will saturate the camera's sensor and not be retrievable if you expose too hard to the right. If you under-expose to maintain detail in the whites you will invite noise and end up with a dingy image, so it is difficult to win under these circumstances - so be satisfied with a compromise. The image has more dynamic range than the camera can handle - the only real option is to retake the image on a more overcast day when contrast will be lower.

Let's just hope that the camera manufacturers find ways of increasing the dynamic range of digital sensors to more closely match the range that our eyes can comprehend and our brains interpret.

TIP

If you found this tutorial useful, I strongly recommend that you next read my tutorial on
Working at high ISO - as it makes maximum use of exposing-to-the-right to achieve high
shutter speeds without incurring the penalty of large amounts of digital noise in your images.