Chobial
Photography basics

Read a histogram and keep your highlights

Lesson 4 of 8

A phone screen is a poor judge of exposure. It's bright, it changes with the room you're in, and it can make a ruined sky look fine. The histogram is a graph of the photo's brightness that doesn't lie.

The idea

A histogram sorts every pixel by brightness. The left edge is pure black, the right edge pure white, and everything else is in between. The taller the graph at any point, the more of the photo is at that brightness.

Too dark Shadows crushed to black Well exposed Nothing piled at the edges Clipped highlights Sky and lights gone to white
What matters is the edges. A wall of pixels against either side means detail that's gone.

There's no single right shape. A photo of a black cat on a dark sofa should lean left; a beach at noon should lean right. The thing to look for is clipping: a pile-up hard against either edge. Everything in that pile is the same pure black or pure white, with no detail left in it.

Highlights first

The two edges aren't equally bad. A RAW file holds a surprising amount in the shadows: what looks black on screen can often be lifted with Exposure or Shadows in the editor. Highlights are different. Once the sensor is full, it's full. A clipped sky is white in the RAW too, and no editor can bring its clouds back.

That leads to the most useful rule for shooting RAW: expose so the important highlights are just safe, and lift the shadows later.

Zebras

A histogram tells you that something clipped. Zebra stripes show you where. They draw diagonal stripes over any part of the viewfinder brighter than a threshold. If the stripes are on a white shirt or the sky, that detail is at risk. If they're only on a lamp bulb or the sun, that's fine: those should be white.

In Chobial

  1. Open the controls and tap DISP. Four switches come up down the left.
  2. Turn on Histogram. It appears in the bottom corner, with the overall brightness and the red, green and blue channels.
  3. Turn on Zebra. Set how bright a highlight has to be before the stripes appear in Settings › Clipping Threshold.

The viewfinder's histogram measures what the sensor records, before the film is applied, because that's what ends up in your RAW. After the shot, open a photo and tap ••• › Show Histogram in the editor. That one measures the developed photo, film and edits included, so it shows what will clip in the file you export.

Expose for the sky

  1. Find a scene with bright sky and something darker in front: a tree, a building, a person in shade.
  2. Turn on Histogram and Zebra. Tap the dark subject. The camera brightens for it, and the sky probably fills with stripes.
  3. Drag the EXP dial down until the stripes on the sky disappear, or only cover the sun. Take the photo. It'll look too dark. That's expected.
  4. Open it, tap edit and use the Light tool: raise Shadows and Exposure until the subject looks right. The sky keeps its clouds.
Want the sky and the subject handled separately? A sky mask lets you edit the sky on its own, and a face mask brightens only a face.

Next, colour: why photos turn orange or blue, and how to decide which way they should lean.

Questions

Should the histogram be a hill in the middle?

Only if the scene is mostly mid-tones. A snowy field should sit to the right and a night street to the left. What matters is the edges: whether anything important is piled up against them.

Why do the red, green and blue channels differ?

Because the scene has colour. A red flower can clip in the red channel while the overall brightness looks fine, and the petals lose their detail. If one colour hits the right edge, bring exposure down a little.

Why doesn't the camera histogram change when I switch films?

On purpose. The viewfinder's histogram measures what the sensor records, before the film. That's what decides what's in your RAW. The editor's histogram measures the developed photo, film included.