Glance at the summary firstThe summary from the end of the lesson, as a road map before you start reading.
At the bright end, areas that reach the sensor's limit get the same pure white value and their detail doesn't come back; at the dark end, detail can be rescued to some extent even if it is mixed with noise, but completely black areas are lost too. The highlight warning shows areas about to blow out after the shot, and zebra stripes during the shot; what matters is deciding whether the blinking area is a detail to protect or an acceptable glint. On faces, you need to keep bright points such as the forehead and nose from blowing out on every skin tone, and protect the shadows of dark skin without pushing them to the left edge; when rescuing both ends at once isn't possible, you need to change the light or consciously decide which end to protect.
Learning goal
You will be able to see the limits of overexposure and underexposure at the moment of shooting. You will explain why an area recorded as completely white can't be rescued, and why a dark area can be opened up to some extent; you will turn on and read the blown-highlight warning on the review screen and the striped pattern at the moment of shooting; you will decide whether the blowout the warning shows is in an important area or in an acceptable glint; and on faces, whatever the skin's tone, you will make sure the shining points and the shadows are recorded without getting lost.
The question
You are looking at a photo, and part of the sky is a pure white void; no cloud, no color. You open the editing app and pull the highlights slider, but that area only turns into a flat gray. In the same photo there is a dark corner; when you open up the shadows, a chair and a cat appear there, a little grainy but visible.
Can a blown-out photo be rescued? The answer to this question is different in the two directions: detail lost at the bright end usually doesn't come back, while detail left at the dark end can be brought back at a price. In this lesson we will talk about this asymmetry, how the camera warns you against blowouts, and how to use these warnings at the moment of shooting.
Context
In the editing module you saw that a window blown out to pure white doesn't come back, and in the exposure module that overflowing buckets lose detail. In the previous lesson you learned that the histogram pressing against an edge is this loss's trace on the graph. This lesson carries that knowledge to the moment of shooting: seeing the loss while shooting instead of noticing it after the photo is taken.
Cameras and many phones have two tools for this. One is the highlight warning, which shows blown-out areas with a blinking pattern when you review a photo you have taken. The other tool is zebra stripes, a striped pattern that appears on the screen or in the viewfinder before the shot. Both usually come switched off in the menu and need to be turned on once. Once they are on, they show exactly where in the photo the thing the histogram tells you is.
Simple explanation
Why don't blown areas come back, and why do shadows?
Each point of the sensor can record a certain amount of light. All the points that reach that limit get the same value, that is, pure white. A light cloud and a bright sky can no longer be told apart once they reach the limit; both are the same number. Pulling down the highlights in editing only turns this number gray, because there is no detail inside it. These are called blown highlights. RAW files can leave a little more room at the bright end than the JPEG preview shown on the screen; but even they can't rescue an area that has reached the sensor's own limit.
At the dark end the situation is different. Points that get little light record not zero but a small value; there is detail in these values, but it is mixed with noise. When you open up the shadows, this detail comes back, but the noise grows along with it. That is why there is shadow latitude at the dark end: up to a certain point you can rescue it, and beyond that, grain drowns the detail. Areas recorded as completely black, just like blown whites, don't come back. The difference is this: the bright end stops at a sharp wall, while the dark end is a slope that slowly breaks down into noise.
How do you read the highlight warning?
When you review a photo you have taken on the camera's screen, the highlight warning shows blown-out areas with a blinking black or colored pattern. On many cameras it is turned on in the playback menu. Once it is on, every time you look at a photo, the areas recorded as pure white blink as if winking. This warning shows exactly where in the photo is the place where the histogram says it presses against the right edge.
When you see the warning, the question to ask is: does the blinking area matter? The sun itself, the filament of a bulb, small glints on water or a reflection on a car's chrome may be blown out; these should look pure white anyway. But if the lace of a wedding dress, the clouds of a sky or the forehead of a face is blinking, that detail is being lost, and you need to bring the exposure down a little. Because the warning is calculated from the JPEG preview, it is a little cautious when you shoot RAW; still, using it as a safety margin is the safest way.
What are zebra stripes for?
Before the shot, on the screen or in the electronic viewfinder, zebra stripes draw a striped pattern over areas above a certain brightness. They are common on mirrorless cameras and video cameras; they are also found in the pro modes of some phones. The difference from the highlight warning is that they show the result without shooting: the moment you see the stripes you adjust the exposure, then you shoot.
On many cameras the zebra threshold can be adjusted. When you set the threshold to the highest value, the stripes appear only in areas about to blow out; this is a live counterpart of the highlight warning. Some photographers, and especially people who shoot video, set the threshold to a lower value and use it to watch the bright points on faces; when the stripes start to appear on the brightest part of the face, they know the exposure is generous enough for the face. Which value to set the threshold to changes with the camera and the shooting style; you should find it on your own camera with a few tries.
What can get lost on faces?
The places on a face that blow out most easily are the small areas that reflect the most light: the forehead, the tip of the nose, the cheekbones. On light skin these areas quickly turn into pure white patches, and the highlight warning makes them blink. On dark skin too, a sweaty or oily forehead can give a bright reflection under strong light and blow out in the same way; this specular highlight can blink even if the rest of the skin is correctly exposed. You decide whether a reflection is a small glint or a patch whose texture has been lost by zooming in on the face and looking.
In underexposure, on the other hand, the risk is in the shadows. The shaded cheek of a dark face comes closer to the left edge as the exposure is brought down; when it is opened up later, it gets blotchy with color noise. That is why, while bringing the exposure down to prevent blowouts, you must not overdo it: bring it down enough to rescue an important blinking area, but not so much that it pushes the shadow of dark skin to jet black. Sometimes rescuing both ends at once isn't possible; then either you change the light, for example by moving the person into the shade, or you consciously decide which end to protect.
Visual evidence
Imagine photographing a fishing boat at dawn. The boat's hull is white, and behind it is a sky glowing with the rising sun; on deck, a fisher with sun-darkened skin is gathering in their nets. As you review the photo you took in auto mode, the highlight warning blinks over both a large part of the sky and the boat's hull. A small point on the fisher's forehead is blinking too.
You set compensation to minus one and shoot again. In the sky only the area around the sun is blinking; the clouds and the texture of the boat's paint have come back. The point on the fisher's forehead is now a reflection, and its texture can be made out. But the shaded side of their face is dark; the histogram has come closer to the left. In editing you open up the shadows with restraint; the face appears with the skin's own warmth, with a slight grain that doesn't catch the eye. When, out of curiosity, you also try minus two, the shadow of the face sticks to jet black, and when opened up it turns into a blotchy gray. In this scene, the right point was the balance between a blown sky and a lost shadow.
Common mistakes
Common mistakeTrying to rescue a blown sky in editing.
No detail is recorded in a completely white area; whatever the setting, it stays a flat surface. The fix: turn on the highlight warning and shoot without important areas blinking.
Common mistakeTrying to fix every blinking point.
The sun, bulbs and small glints should be white anyway. The fix: prevent blowouts only in areas whose detail matters.
Common mistakeBringing the exposure down too far to prevent blowouts.
Shadows stick to jet black, and when opened up, dark skin turns into a blotchy gray. The fix: bring it down enough to rescue the important bright area, but not so much that the shadow sticks to the left edge.
Summary
At the bright end, areas that reach the sensor's limit get the same pure white value and their detail doesn't come back; at the dark end, detail can be rescued to some extent even if it is mixed with noise, but completely black areas are lost too. The highlight warning shows areas about to blow out after the shot, and zebra stripes during the shot; what matters is deciding whether the blinking area is a detail to protect or an acceptable glint. On faces, you need to keep bright points such as the forehead and nose from blowing out on every skin tone, and protect the shadows of dark skin without pushing them to the left edge; when rescuing both ends at once isn't possible, you need to change the light or consciously decide which end to protect.
Mini assignment
In this assignment you will turn on the blowout warnings and use them.
- Turn on the highlight warning on your camera, and zebra stripes too if it has them; look for a similar option on your phone.
- Shoot a scene containing a bright sky or a white surface in auto mode, and note the blinking areas.
- Shift compensation step by step toward minus and keep shooting until important areas stop blinking; at each step, look at how much the shadows darken.
- Shoot a portrait of a friend in bright light and check whether there are blinking points on their forehead and nose, and whether their shaded cheek drops to jet black.
Check yourself
- Were you able to tell which of the areas the highlight warning made blink were important and which were acceptable?
- While bringing the exposure down, did you find the point where the shadows stuck to the left edge?
- On your friend's face, whatever their skin tone, did both the bright points and the shadows keep their detail?
Glossary
| Term | Short definition |
|---|---|
| Blown highlights | Areas that reach the sensor's limit and are recorded as pure white, whose detail doesn't come back. |
| Highlight warning | A review feature that shows blown-out areas in a photo you have taken with a blinking pattern. |
| Zebra stripes | A striped pattern drawn during shooting over areas above a certain brightness. |
| Shadow latitude | How far dark areas can be opened up before grain increases. |
| Specular highlight | A small reflection, much brighter than its surroundings, coming from a sweaty forehead or a shiny surface. |
Mini quiz
1. Why can't a sky recorded as completely white be rescued in editing?
- A) Because editing apps don't recognize the sky
- B) Because all the points that reach the sensor's limit get the same value and no detail is left inside them
- C) Because the sky is always blue
- D) Because a RAW file was used
2. What is the basic difference between the highlight warning and zebra stripes?
- A) The highlight warning only works in video
- B) Zebra stripes only show black areas
- C) The highlight warning shows areas about to blow out after the shot, zebra stripes during the shot
- D) Zebra stripes are only found on phones
3. If the highlight warning only makes the filament of a bulb blink, what should you do?
- A) Usually nothing; the bulb should look pure white anyway
- B) Bring the exposure down two stops
- C) Delete the photo
- D) Turn off zebra stripes
4. On dark skin, what can bringing the exposure down too far to prevent blowouts lead to?
- A) The skin turning pure white
- B) The white balance going wrong
- C) The reflection on the forehead growing
- D) The shadows sticking to jet black and turning into a blotchy gray when opened up
Answers
- B — All the points that reach the limit are pure white; the difference between cloud and sky is no longer recorded, and the slider only turns it gray.
- C — The highlight warning shows areas about to blow out while you review a photo you have taken, zebra stripes on the screen before the shot.
- A — Bulbs, the sun and small glints should be pure white anyway; their blowing out doesn't count as a loss of detail.
- D — Exposure brought down too far pushes the shadows to the left edge; when they are opened up, the noise grows and the dark skin slides into a blotchy gray.
Summary card
- A blown white doesn't come back; shadows can be opened up to some extent.
- Highlight warning: blown areas blinking after the shot.
- Zebra stripes: stripes on areas about to blow out, during the shot.
- Does the blinking area matter? It can be the sun or a bulb; it shouldn't be a cloud or a face.
- Don't blow out the bright points, don't push dark skin's shadow to jet black; change the light if needed.
Bridge to the next lesson
On the fisher's boat we were caught between rescuing the sky and protecting the shadow of the face. The reason for this squeeze is that the range of light the sensor can record in a single frame is narrower than the range the eye sees. The next lesson describes this limit, dynamic range, and why the sky so often comes out pure white.