Wildlife photography by John Devries, Kent UK. Inspirational images
Basic image adjustments tutorial-
Levels and histograms
The histogram on the back of your camera is one of the most useful
but under-used features on a modern digital slr camera. I am surprised
that many seasoned photographers don't seem to understand it - or
it's benefit. It all looks a bit technical, so many shy away from
using it. In actual fact it is your best ally in getting correct exposures
in your pictures.By the end of this tutorial you will love it - trust
You will also come across the histogram again in Photoshop - both
in the RAW converter and in the Levels dialogue box - so there is
no escaping it - you are going to have to come to grips with these
mysterious looking graphs! But don't worry - they are not half as
bad as they look
If you have shot your images in RAW, then you will have already made
your basic image adjustments in the raw converter software as described
in the "art of raw conversion"
tutorial , you will already have come across the histogram and used
it to adjust your image's tonal values. What follows is useful for
subsequently tweaking your brightness/contrast and colour balance
to make your pictures really "pop".
If you shot the images in jpeg format, then the following is an essential
basic procedure as your images will look dull, washed out and lacking
contrast and impact without it. Additionally, your images may have
a colour cast if you did not get the white balance spot-on at the
time of shooting.
Adobe Photoshop's Levels command lets you correct the tonal range
and colour balance of an image by adjusting intensity levels of the
image's shadows, midtones, and highlights. In this tutorial, you'll
learn how easy it is to do in a simple three step process.
The levels dialogue box, first look at the histogram
and how to use it to adjust an image to look much punchier.
1. Open your image in Photoshop.
Choose File > Open or double-click a thumbnail in
the File Browser in Photoshop CS or Bridge in CS2.. Before you start
making adjustments, evaluate the image tonality. Is it too light or
dark? Does it have too much or too little contrast? Is there a color
2. Create a new Levels adjustment layer.
Choose Layer > New Adjustment Layer > Levels,
and then click OK in the New Layer dialog box. You can also open the
Levels command by choosing Image > Adjustments > Levels. However,
with an adjustment layer, you are applying the tonal correction on a
separate layer. The original image is untouched. If you decide you don't
like your changes, you can change them at any time or simply discard
the adjustment layer and return to your original image.
Enter the histogram....
A very useful tool for evaluating an image's tonality is the histogram
displayed in the Levels dialog box. A histogram illustrates graphically
how the pixels which go to make up an image are distributed, by mapping
the number of pixels at each color intensity level. In other words
it shows you the distribution of pixels in the image in graphic form.
The shadows are shown in the left part of the histogram, the midtones
are shown in the middle, and the highlights are shown in the right
part of the graph.
In this image of a mute swan you can see the distribution of pixels
in the histogram - those to the extreme left represent the very small
number of pixels that are very dark (the black on knob of the swan's
beak for example). The bulk of the pixels are in the midtones (which
represent the water and reeds). The area to the extreme right represents
the highlights - and notice that they are bunched right up to the
right of the graph and beyond. You may have noticed that there is
also a tall spike at the extreme right of the box.. This is indicative
of over-exposure, the highlights are "blown or clipped "
If you look at the swan itself, you can see that this area corresponds
to the wing and tail - which has burnt out to pure white and it is
not possible to distinguish the feathers - not good.
Now look at the shadow part of the graph. It is not clipped at this
exposure level, so in this example, it would have been better to have
underexposed the shot by around half to one f-stop at the time of
shooting it in order to retain the missing highlight detail. This
would have driven the graph to the left - at the expense of the shadow
detail. If we overdid it, the shadows would then start to clip !
This scene of the swan is very "contrasty" as it is in full
sunshine - i.e. has a very large dynamic range. That is to say, the
blacks are very black and the whites are very white and shadows are
strong and harsh under such conditions.
A bright-overcast day offers less contrast than full sunshine and
is often preferable for photographing white subjects - where your
aim is probably to retain detail in the shadow and highlight extremes.
On a really grey day, the contrast is lower still - blacks look greyer
and highlights also look greyer, so it becomes easy to capture the
full dynamic range of the scene, but as grey days offer very "flat"
lighting with few shadows, pictures tend to look bland and unexciting.
Another way of lowering contrast is to use a reflector or fill-flash
to lighten the shadows - but this would not have been very practical
with our swan example.
You will quite often find that you will come across scenes which have
a greater tonal range (dynamic range) than the camera can handle -
both shadows and highlights are clipping. Under these circumstances
you will have to decide which are more important to your image and
expose accordingly. It is possible to combine over and under-exposed
images together in Photoshop to produce a high-dynamic range (HDR
image) but this is beyond the scope of this tutorial.
If your camera is a digital slr, you should be able
to check the histogram on the back of the camera immediately after taking
the shot. Look for "clipped" highlights or shadows and adjust
the exposure accordingly and retake the shot if necessary. Some cameras
have a setting where you can set the highlights to blink in the areas
The correctly exposed shot
The next image of a collared dove is perfectly exposed - no clipped
highlights or shadows, it was easy for the camera to get this right
as the scene is predominantly mid-tones with no extreme highlights
or shadows to cause problems of clipping. The full "dynamic range"
of the scene has been captured. Even so, we can improve the look of
this image and give it far more "punch" by adjusting the
levels a bit. So let's pep it up:
Adjusting the levels by setting the shadow and highlight
1.0 Move the Black Point Input slider (located directly beneath the
histogram) inward from the edges of the histogram. Moving the Black
Point Input slider maps all image values at its position or below
to the Output Levels black point (set by default to 0, or pure black).
This will blacken up the shadows and add more of a contrasty feel
to your image, but don't overdo it - as you will losing shadow detail
in the process.
2.0 Similarly, moving the White Point Input slider maps image values
at its position or above to the Output Levels white point (set by
default to 255, or pure white). For example, if your image is too
dark, move the Input White Point slider to the left. This maps more
values in the image to 255 (the Output Levels white point), making
them lighter. If there are important highlight details in this part
of the histogram - such as subtle detail in the feathers of a swan,
you will loose them - as you are making these values pure white, so
be careful. In this example of the dove, the pale areas around the
bird's eye and chin will be sacrificed just a little to give the image
a little lift.
A good starting point for many images, is to adjust the sliders up to
where the histogram begins to rise steeply at each end as I have done
above example. Compare the two images of the dove and you will see how
washed-out the first image looks compared to the adjusted one.
As you move the highlight slider you will notice that the middle (midtone)
slider adjusts itself automatically - which is useful.
3.0. Adjust the midtones in the same way by moving the middle input
slider to the left to lighten the image or to the right to darken the
image in the mid-tones. The middle input slider actually adjusts the
image gamma. It moves the midtone (level 128) and changes the intensity
values of the middle range of grey tones without dramatically altering
the highlights and shadows.
That's all there is to it. When finished click OK to apply the
levels adjustments - job done.
4.0. Removing color casts within levels.
Select the Set Grey Point Eyedropper tool in the Levels dialog box.
Click an area in the image that contains only a grey tone, or an area
containing as few colors as possible. It's easier to color balance
an image by first identifying an area that should be neutral and then
removing the color cast from that area. With such a correction, all
other colors in the image should be color balanced, too. The eyedropper
tools work best on an image with easily identified neutrals.
If there are no easily identified neutrals in your image, the Levels
command may also be used to adjust individual colour channels (red,
green or blue) to remove a color cast. Choose a channel from the Channel
menu of the Levels dialogue box and then adjust the Input sliders
for either red, green or blue.Many images with a blue sky in the picture
benefit from moving the blue channel slider a little to the left in
the highlights - it really perks up the sky - try it for yourself.
The under-exposed shot
This image of a nuthatch was purposely under-exposed to illustrate
a point. (Well that's my excuse and I am sticking to it) :
See how the shadows are clipped off at the left hand side of the graph
? The mid-tones are bunched up to the left, and the highlights are most
definitely not clipped - they seem to drag on forever along the baseline.
Can the levels adjusters deal with this situation and retrieve the
image ? The answer is essentially yes, but there is a price to pay in
terms of " noise". Digital noise is the unsightly equivalent
of film grain and is usually concealed within the dark areas of the
image. If we open up the shadows and midtones using the levels sliders,
this will expose the noise to the detriment of the image. If the image
was really precious to us, there are several good noise-reduction filters
available (such as Neat Image, Noise Ninja and Photoshop's own noise
filter) which will help a lot in reducing noise without loosing too
much detail and sharpness in the image.
To demonstrate this noise, here is the adjusted image of the Nuthatch
at 200% so you can see the noise in the red-circled area .I have purposely
over-sharpened the image a bit to show it more clearly here.
Below is the equivalent from the correctly exposed image. Notice how
the noise in the circled area is much lower. It is difficult for me
to illustrate this very clearly on this website as the images are such
low resolution here, but hopefully you can get the general idea. The
examples are using images shot at low ISO (200). If they had been shot
at high ISO in order to gain shutter-speed on a dull day the noise would
have been much worse.
More histogram examples
Let's look at a few more histograms and endeavor to interpret what
they are telling us:
Here is an easy image for the camera to get right - it is predominantly
midtones (hence the huge mid-tone peak) - all the highlights are captured
without clipping. There is a bit of clipping in the extreme shadow area
to the left of the histogram - but this only represents the few black
shadows between the planks which I am more than happy to allow to go
to 100% black as they are non-critical and it even gives the image a
bit of punch.
This is an image of a Puffin. The histogram looks very different to
the last example. The three peaks to the right of the histogram represent
the white on the bird, the sky, and I am guessing here - the pale coloured
rocks. Notice that the three peaks are taller than the box ? This simply
means that they go outside the scale of the box - they are not actually
missing or clipped - and this is nothing to worry about.
The image looks a little bright at first, but the histogram tells us
that we have (just) captured the full dynamic range of the image. I
would simply adjust the midtone slider a little to darken the image
- which will minimise noise and make a great picture. This is a good
example of "exposing to the right " in action - click here
to see the tutorial on exposing to the right.
This example also illustrates that histograms can look very different
according to the scene - sometimes smooth and rounded - sometimes spiky
like this one. There is not a right and a wrong as such - histograms
just are !
This is a night image of Tower Bridge in London. At a first glance
at the histogram, it looks under-exposed.
The image has a lot of dark night sky which has clipped to black, but
I like the contrast that gives to this image - so that is fine by me.
The midtones are mainly to the left of the image - which would normally
suggest under-exposure, but look at the highlights - which are important
in this picture - they too are starting to clip at the extreme end (the
lights on the top of the building). I don't mind them clipping - as
I am happy with them being pure white on this occasion. What I don't
want is the light on tower bridge itself to clip - which it isn't .
So despite the initial appearance of this image being under-exposed,
it is not, at least it is not within the concept of what I am trying
to achieve with the image.
Now let's say that I wanted to show a bit more light in the sky rather
than the pure black that it is. Then I would say that the image is
under-exposed! I would have needed to have shot the image with a little
positive exposure compensation (say plus 2/3 of an f-stop). As I didn't
I could now try opening up the shadows with the midtone slider, but
I would soon start to expose unacceptable levels of noise in the image.
So which is it - underexposed or not underexposed ? The answer depends
entirely on what you are trying to achieve. Histograms are not always
showing you right and wrong - they just showing you how it is - and
you have to decide if it's right for you - this is supposed to be art
after all !
Hopefully this tutorial has given you an understanding of the histogram
and how you can harness it's power to make better pictures
Good luck !
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