Expose to the right
The darkest tone available is zero, and shown at the left-hand side of the graph. The lightest, whitest tone achievable is 255 on the scale – and is shown on the extreme right of the graph.
The steps along the x-axis then fill in all the possible shades in between. The vertical y-axis then simply shows the number of pixels of each brightness.
Contrary to popular opinion, there is no such thing as an ‘ideal’ histogram. Some subjects will give shots that simply have more brighter tones than others – and ultimately no two histograms will be identical.
It’s the overall shape of the graph that is your secret weapon for assessing the shot’s exposure and contrast.
To get the best tonal range, and to avoid problems with underexposed shadows or overexposed highlights, the histogram should be vaguely bell-shaped. That is, the graph should drop down to baseline towards both left-hand and right-hand extremes.
What you should try to avoid is an image with the graph stacked to the extreme right or left – as this suggests that detail has been lost or ‘clipped’ in the highlights or shadows.
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