Strengths and weaknesses of a phone

Learning goal

You will be able to say, with concrete examples, in which conditions a phone camera can compete with a camera and in which it falls behind. You will recognize where the problems that appear in the dark, with distant subjects and with fast movement come from, and the traces the phone's processing leaves on the photo when it tries to hide those problems; and by drawing a limitation map for your own phone, you will be ready for the solutions you will learn in the next lessons of this module.

The question

Imagine going to your child's football match on a Saturday. In the morning warm-up the sun is shining; the photos you take with your phone are great: vivid colors, sharp faces, bright green grass. In the evening the match continues under floodlights. In the frames you take with the same phone, the players have turned into blurry trails, the goal-scoring moment at the far end of the pitch is a small, smudgy image, and one player's arm appears twice.

Where does your phone camera let you down? Both the morning's success and the evening's disappointment come from the same phone. In this lesson we will map in detail where the phone is strong and the three situations in which it struggles: darkness, distance and fast movement. A photographer who knows their limit can change course before hitting it.

Context

For many people today, taking a photo means taking the phone out of their pocket. There is a good reason for that: the phone is always with you, it is easy to use and in most situations it gives surprising results. In the previous modules you saw why a small sensor and densely packed pixels create limits. In this module we turn that knowledge into practice: using the phone like a camera, deliberately and to suit your purpose.

The first step to using a phone well is getting to know its character. Phone makers try to make up for the small sensor with powerful processors and clever software. That compensation often works, but not always. Being able to tell the situations where the software succeeds from those where it fails is the most important knowledge for the quality of a photo taken with a phone. This lesson is the map of that distinction; the following lessons will show in detail what to do in each region.

Simple explanation

Where is a phone strong?

A smartphone camera's biggest strength is that it is ready. It is in your pocket, it opens in a few seconds and nobody finds it as eye-catching as a camera. On the street, at a family dinner or during a child's game, people behave more naturally in front of a phone. This is an advantage a professional camera often can't provide.

In plenty of light, the phone's small sensor creates almost no disadvantage. When enough light falls on the sensor, noise isn't a problem, and the phone's processor adjusts colors, contrast and sharpness skillfully. One side effect of the small sensor also helps here: a wide area stays sharp from front to back. In a landscape, a document photo or a group photo, having everyone and everything sharp is easy with a phone. Phones can also focus very close; you can photograph the inside of a flower or the texture of a fabric from a few centimeters away. Combining several frames to balance a bright sky and a shaded foreground in the same frame is another of the phone's strengths; we will open this up in Lesson 4.5.

Why does it struggle in the dark and at a distance?

When light falls, the small sensor's limit shows at once. To hide the noise that comes with little light, the phone either stacks and combines several frames or smooths the image. If you or the subject move during the combining, the image blurs. Smoothing, on the other hand, wipes out fine details: strands of hair turn into a mass, the texture of fabric into a flat surface. The trace of smoothing shows most on a dark cheek in shadow: the pores and fine hairs are wiped away, and the skin turns into a surface as smooth as wax but lifeless. Some manufacturers have announced in recent years that they have recalibrated their processing software to show different skin tones more accurately; even so, checking the result with your own eyes is the most reliable way.

With distant subjects the problem comes from somewhere else. Most phones have more than one camera, and one of them may carry a lens that brings distant things closer; but that lens has a limit too. When you go beyond that limit, the phone turns to digital zoom, that is, it cuts out part of the image and enlarges it. The result is a smudgy image without detail. You will see separately in Lesson 4.6 which camera comes into play when, and how to switch to the right one.

Why does it struggle with fast movement?

Movement is the phone weakness we talk about least. The main cause is light again: as light falls, the time the phone spends gathering light grows longer, and a running foot draws an arc in that time. But other factors are involved too. Most phones read the sensor not all at once but line by line, from top to bottom; this is called a rolling shutter. This reading takes a very short time, but something moving very fast, such as a propeller or a train rushing past, changes position during that time and looks bent and twisted in the image.

Moving subjects also confuse multi-frame processing. If a player's arm is in a different place in each frame while the phone combines several frames, in the final photo the arm can appear twice or as a semi-transparent ghost trail; this is called ghosting. The double arm you saw in the evening match photo is why. There are ways to reduce these problems: adding as much light as possible, catching the moment when the movement starts or stops, using the phone's burst or sports mode. But first you need to know that this limit exists.

Visual evidence

Picture two photos from match day side by side. In the frame taken during the morning warm-up, the sun hits from the side. The players' faces are sharp, the numbers on their shirts can be read, individual blades of grass can be made out. The trees and the stand in the background are sharp too; because everything is sharp the frame is a little crowded, but lively. It is hard to tell apart from a photo taken with a camera.

In the frame taken in the evening under the floodlights, the same players are running fast. The faces are soft and without detail; the face of the goalkeeper, who has dark skin, is almost a flat smudge in the shadow. The foot of the player kicking the ball is a blurry arc, and their arm appears twice, along with a semi-transparent ghost. In the frame where you zoomed in on the goal-scoring moment at the far end of the pitch, the players are small, colored smudges; the goal nets can't be made out. The same phone, the same patience. The strength of the morning frame comes from plenty of light, while the problems of the evening frame come from darkness, distance and speed arriving together.

Common mistakes

Summary

A phone camera is strong in plenty of light, in scenes that need a wide sharp area and in close-ups; being always with you and putting people at ease is also a big advantage. It struggles in the dark because of its small sensor, at a distance because of digital zoom, and with fast movement because of line-by-line reading and multi-frame combining; knowing these limits is the first step to using a phone deliberately.

Mini assignment

In this assignment you draw the limitation map of your own phone.

1. On the same day, take four frames: one in daylight, one in a dim room, one zooming in on a distant subject, and one of a moving subject, for example a running child or a cyclist.
2. Zoom in on the four frames on the screen and note in each where the detail is lost and where noise or smoothing begins.
3. In the moving frame, look for ghost trails, double images or bending.
4. Write in a single sentence the situation where your phone is strongest and the one where it is weakest, and guess which lesson of this module will give a solution to that weakness.

Check yourself

• Were you able to shoot all four conditions with the same phone and compare them?
• In each frame, could you tell whether the problem came from darkness, distance or movement?
• Did you save your limitation map on your phone or in a notebook?

Glossary

Mini quiz

1. In which condition does a phone camera compete most easily with a camera?

• A) When photographing moving people in a dim hall
• B) When photographing still or slow subjects in daylight
• C) When photographing a very distant bird
• D) When photographing a car speeding past at night

2. Why can a moving subject leave a ghost trail in night mode?

• A) Because night mode turns the photo black and white
• B) Because the phone takes only a single frame
• C) Because while the phone combines several frames, the subject is in a different place in each one
• D) Because the screen brightness is low

3. Why does a fast-spinning propeller look bent in a phone photo?

• A) The lens is dirty
• B) The propeller changes position while the sensor is read line by line
• C) The photo is saved as a JPEG
• D) The propeller really is bent

4. How can the phone's smoothing in low light affect a darker-skinned face?

• A) It always makes the face sharper
• B) It makes the face look completely white
• C) It has no effect
• D) It can wipe out the pores and fine texture and leave the skin waxy and lifeless

Answers

1. B — In plenty of light the small sensor isn't pushed into noise and the phone's processor adjusts colors and sharpness skillfully; darkness, distance and speed are what push the phone.
2. C — Night mode gathers frames over several seconds; when the subject moves, it stands in a different position in each frame and appears doubled or semi-transparent in the combined image.
3. B — A phone sensor is read line by line from top to bottom; in that short time a fast-spinning propeller changes position, so it looks bent and twisted in the image.
4. D — The smoothing done to hide noise wipes out fine detail; on a dark cheek that gets little light, pores and fine hairs are the first details to disappear.

Summary card

• The phone's strength: always with you, brilliant in plenty of light, a wide sharp area, very close focus.
• Darkness: small sensor → noise → smoothing or combining.
• Distance: digital enlargement past the limit of the zoom lens.
• Movement: long exposure, line-by-line reading and ghost trails.
• Zoom in on important frames and look closely at the faces.

Bridge to the next lesson

You have mapped the phone's limits. But sometimes the problem is neither darkness, nor distance, nor movement; the photo comes out behind a misty veil and the cause is much simpler. The next lesson asks: why do phone photos sometimes come out hazy? There you will see how the most common killer of quality hides on the glass of the phone in your pocket.