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Beecher's Handouts >

13 – Histograms

Beginners should come back to this section later.

Definition

Many cameras can display histograms.

A histogram is a graph of how many pixels there are at different brightness levels.

The bottom axis is brightness.

The shadows are to the left and highlights are to the right.

The left axis is the quantity of pixels at each brightness level.

Examples

Here's the histogram for white hydrangea flowers on sunny day.

The dark corner on the right side of the photograph is to the left on the histogram.

The leaf pixels are in the middle, as they have a medium brightness.

The flower pixels that are in the sun are to the right.

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Here's a histogram of eggs taken on an overcast day.

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Because the scene has a medium to medium-high brightness, the graph is taller in the middle and to the right.

Here's a histogram of black velvet.

Because the fabric is so dark, the graph is tall on the far left side.

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Histograms & Exposure

You can use histograms to judge exposure.

You don't want to under- or overexpose photographs.

Here's the histogram for the normal exposure for castor bean leaves.

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There are shadows (left side) and midtones (middle).

There are no highlights (right side).

There are no spikes at either end.

Therefore, there's no clipping.

It's a good exposure.

The next histogram shows pronounced overexposure of the leaves.

Note the tall spike at the right side of the histogram.

The spike is called clipping.

Clipping means that no image data has not being recorded.

You can't edit areas that are clipped.

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The next histogram shows severe underexposure.

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Note the tall spike at the left side of the histogram.

Again:

• The spike represents clipping.

• Image data has not been recorded.

• You can't edit in the clipped areas.

Note

Not all clipping is bad.

If the area that's clipped is unimportant, it's okay to be clipped.

Highlights

If the clipped highlights are on some dew drops, it doesn't matter.

You won't need to be editing those highlights.

However, if the clipped highlights are on someone's face, clipping does matter.

Shadows

If there's a clipped shadow under a car, it probably won't need to be edited.

Therefore, clipping is okay.

However, if there's an alligator in the clipped shadow, clipping does matter.