Reading A Histogram Correctly
Digital technologies make photographer's work more efficient and quick.
Today digital cameras can even perform analysis of the shots that
you've just taken, showing us overexposed areas on the histogram (general histogram and separate for each of the 3 RGB
channels).
A histogram allows a photographer to carry out initial
image analysis and make corrections in the shooting process. It would
help you not to stick to additional post-processing in RAW Converter
and Photoshop.
A histogram
is a graphical representation of the tonal distribution in a digital
image. The horizontal axis of the graph represents tonal variations,
while the vertical axis represents the number of pixels in that
particular tone. For example, if on the left there aren't any pixels, so there will be no black areas on the photo.
A histogram is read from left to right, from black to white.
Look at the following examples below, and you will understand how we
can read the histogram.
There are no 100% dark
areas in the image.
But on the right some highlighted areas are shown.
In general our histogram is distributed evenly along the whole range of
brightnesses. We do find some overexposed and underexposed areas, but
they are not so critical.
In the next example you can see how we can read underexposed and overexposed areas on the histogram.
On the display it won't be possible to see, how much depth of white you
have in the background. The histogram shows a complete blacks on the
laptop screen, white and gray tones of its body and
white background around the object.
Looking
at the camera screen it is difficult to understand if we have any information falls on the car body. The histogram is showing clearly that there are
no 100% dark areas, but we do see overexposure on the white objects.
A histogram helps you during post processing in Photoshop in Levels mode.
Look at how the histogram is changed after the contrast increase. It stretches the histogram and adds dark and light areas.
The original photo and the photo with the increased contrast level.
Why do we need a histogram
Almost
every modern camera has a large display. But every display has its own
brightness level, and its perception depends on surrounding light.
If you look at the display at night, your picture would look brighter than
if it was at the day light. Thankfully, histogram shows an image as a
graph, being absolutely independent from viewing conditions.
The
quality of displays in cameras is generally on the high level, but still
not enough to reflect the difference between almost white and
absolutely white color, just as the difference between almost black and
absolutely black color.
Look at this photo. As
you see, there are no over- or underexposed areas here, that's proved
by the histogram. At the borders there are short columns,
indicating overexposure from the street lights and dark areas on the showcases. We can admit that these areas should have such an exposition. But the rest of the information is given in the mid tones in our histogram. So,
one glance on the graph would be enough to assess the right exposure and keep on shooting.
As you understand, each image has its own
histogram, so we cannot say there are right or wrong histograms. It
should be considered as a handy tool of quick image assessment during
shooting or photo editing.
When do we need a histogram
It's quite difficult to define the right brightness and contrast of an image when there's a lack of external lighting.
If you shoot in the studio and you don't have a meter at
hand, you can try to set up the right power mode of the equipment by
looking at the histogram results.
Objects are most commonly photographed on the white background. While a photo can show only the overexposed areas, the histogram will
help you to understand, how much depth of white you have actually got in your
image.
As you see, a histogram is a powerful and handy tool for photographer's
work. Besides, it is an absolutely essential step to create the "right"
pictures from the technical point of view.
You are welcome to ask your questions on our photoforum!
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