Exposure metering: how the camera decides how bright a photo will be

Exposure metering is the process in which the camera measures how much light is in the scene and picks the shutter speed, aperture and ISO so the photo is neither too dark nor blown out. Modes include matrix (evaluative), centre-weighted and spot metering.

Metering point on a face

In plain words

Imagine deciding whether to switch off the lights in a room by looking at just one spot: if it is the window, it will seem there is too much light. Matrix metering is like glancing round the whole room. Spot metering is like looking at one particular face so that it comes out well.

How it works

The sensor assesses the brightness of different parts of the frame.
Matrix metering analyses the whole frame and recognises the scene.
Centre-weighted metering gives priority to the centre.
Spot metering measures a tiny area - a face, for example.
On a phone, tapping the screen sets the metering point and a slider adjusts exposure compensation.

Matrix, centre-weighted and spot metering

Where you'll see it

In the camera's Pro mode, the Metering setting. In auto mode, tap a face so the phone meters from it, and drag the sun slider to adjust.

Does it matter when buying

It is useful in backlight (a person against a window or sunset): tap the face and it will not be a dark silhouette. Or the opposite - lower the exposure to get a nice silhouette and sky.

Myths

Myth: The camera always gets the brightness right. Reality: In tricky light, auto mode makes mistakes.
Myth: HDR completely removes the need for metering. Reality: HDR helps, but the metering point still affects the result.

FAQ

How do I make a face brighter against a window?

Tap the face on the screen and raise the brightness slider.

What is exposure compensation?

Manually making the image brighter or darker than auto mode chose.

What does "blown out" mean?

Areas that have turned completely white with no detail.