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. RAW images have around 1 stop more headroom
in the highlights than jpegs.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
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. However, in this image, there are a lot
of dark tones in the fence rail too, and if I under-expose the
image, I would reveal noise in the shadows and midtones as I re-adjust
the Exposure and Shadow sliders back up again in the RAW converter.
In later versions of Photoshop there is a highlight Recovery slider
beneath the Exposure slider which works really well at retrieving
seemingly lost highlight detail.
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
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
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.
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.
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.