Overexposed video, explained

Exposure is the total amount of light that reaches the sensor for each frame. Three settings control it: the aperture (how wide the lens opening is), the shutter (how long each frame collects light) and the sensor gain, usually called ISO. Phones adjust all of this automatically, and they are tuned to make the average of the frame come out mid-grey.

That averaging is what catches people out. Point a phone at a person in front of a dark wall and the camera brightens everything to lift the wall towards grey, so the face burns out. Snow, beaches, white walls and stage lighting cause the opposite. Most “overexposed” clips are a camera averaging a scene that wasn’t average.

Photographers measure exposure in stops. One stop is a doubling or halving of light. The Exposure control in this tool works in stops too, so −1.0 means half the light, which is a lot: most fixes land between −0.3 and −1.0.

Editors split the range of brightness into rough bands. Shadows are the darker third, midtones the middle (most skin, foliage and walls) and highlights the brightest part: skies, lamps, white clothing, reflections. Whites and blacks are the very ends of the range.

Each control in a grading tool is aimed at one band. In this tool, Highlights compresses the bright band, Whites sets where the very top lands, Gamma moves the midtones, and Blacks sets the bottom. Exposure scales all of them at once. Thinking in bands is the quickest route to a natural result, because over-bright footage is rarely too bright by the same amount everywhere.

Ordinary video stores each colour channel of each pixel as a whole number from 0 to 255 (8-bit), or 0 to 1023 in 10-bit formats. When more light arrives than the top number can describe, the camera writes the top number anyway. Every pixel in a sunlit cloud, a window or a shiny forehead can end up with exactly the same value. That is clipping, and the area is “blown out”.

Clipping destroys information, not just brightness. A clipped cloud isn’t a bright cloud that can be dimmed; it is a white shape with nothing inside. Darkening it reveals no edges because the file never recorded any. This is the single most important limit on fixing overexposed video, and any tool that promises otherwise is inventing detail.

Colour can clip channel by channel. A bright blue sky often clips red and green first, then blue, so before it turns white it passes through a pale cyan. That is why recovered skies sometimes look slightly the wrong colour at their brightest edge.

Dynamic range is the span from the darkest to the brightest tone a camera, a file or a screen can hold, usually given in stops. A sunny street can span 15 stops or more; a typical phone sensor captures around 11 to 13 in one exposure; a standard (SDR) video file and screen show roughly 6 to 8 comfortably. Something has to give, and in a bright scene it is usually the highlights.

HDR (high dynamic range) video keeps more of the top end, using 10-bit values and a transfer curve such as HLG or PQ, and HDR screens can show it brighter than SDR. Most recent iPhones and many Android phones record HDR by default. On an SDR screen, or in an app that doesn’t understand HDR, those clips can look harsh or washed out, because the extra range has to be squeezed into a smaller one.

When you open an HDR clip in this tool, the browser converts it to standard range and the output is SDR. That is often an improvement for sharing: the result looks the same on every device instead of being dazzling on some and flat on others.

People often reach for the wrong slider, because brightness and contrast are easy to confuse. Brightness (or Exposure) moves the whole range up or down. Contrast sets how far apart the tones are. An overexposed clip is usually both too bright and too low in contrast, because the tones have bunched up near white.

• Lowering brightness alone makes the picture darker but leaves it flat, and the blacks turn into a dull charcoal.
• Lowering contrast pulls whites down but also lifts blacks, making the picture greyer, which is the opposite of what washed-out footage needs.
• Raising contrast while lowering exposure and pulling highlights back restores depth: the clip looks darker and clearer at once.

That combination is what Auto fix and the Overexposed look aim for. If you ever find a fix looking muddy, check the darkest part of the frame: deepening Blacks usually solves it.

An 8-bit file has 256 steps per channel. When a fix stretches a narrow band of tones across a wider one, for example the pale top of a sky, those steps get further apart and smooth gradients can show visible bands. Compression makes this worse. The cure is moderation: use the smallest correction that looks right, export at High quality, and if banding still shows in a sky, recover a little less.