Open gate is a recording mode in video cameras that captures the entire usable area of the image sensor, rather than cropping it to a standard delivery shape such as 16:9 or 17:9. Because most sensors are taller than widescreen video, open gate recording typically produces a frame with an aspect ratio close to 3:2 or 4:3, holding extra image information above and below the usual widescreen area.
The term comes from motion picture film, where an open gate meant exposing the full width and height of the film frame without a mask. In digital video, it gives cinematographers and editors maximum flexibility for anamorphic lenses, reframing, stabilization and visual effects.
How open gate recording works
A camera in a standard mode reads only a horizontal band of the sensor that matches the target aspect ratio and discards the rest. In open gate mode, the camera reads every active row and column, so the recorded file has the same proportions as the photosite array itself.
Reading the full sensor has consequences. More rows mean a longer sensor readout time, which can increase rolling shutter skew and sometimes limits the maximum frame rate. Larger frames also produce higher data rates and larger files, so many cameras restrict open gate to certain codecs, such as RAW video or high-bitrate intermediate formats.
The recorded image usually needs a frame line or crop marker in the monitor so the operator knows which part will appear in the final delivery. Without guides, composition can drift because the full open gate frame looks very different from the finished widescreen picture.
Open gate in film and digital formats
The concept has its origin in 35 mm film, where removing the soundtrack mask allowed exposure across the full width of the negative. Digital cinema cameras adopted the name for full-sensor modes. The table compares typical formats.
| Format | Capture area | Approximate aspect ratio | Typical purpose |
|---|---|---|---|
| Academy 35 mm | 21.95 × 16.00 mm on film | 1.37:1 | Classic sound film frame |
| Super 35 full aperture | 24.89 × 18.66 mm on film | 1.33:1 | Film open gate for later extraction |
| Super 35 digital open gate | Full Super 35 sensor area | About 1.55:1 | Anamorphic and VFX work |
| Full-frame digital open gate | About 36 × 24 mm sensor area | 3:2 | Large-format capture and reframing |
| Micro Four Thirds open gate | About 17.3 × 13 mm sensor area | 4:3 | Hybrid and social media production |
A widely used Super 35 cinema sensor records about 3424 × 2202 photosites in open gate, while large-format cinema cameras reach around 4448 × 3096. Hybrid mirrorless cameras often offer full-width 3:2 or 4:3 modes at 5.7K to 8K.
Open gate compared with other sensor modes
Open gate is one of several ways a camera can map the sensor to the recorded file. The differences affect field of view, image quality and processing load, and they are closely related to oversampling and crop modes.
| Mode | Sensor area used | Field of view | Main trade-off |
|---|---|---|---|
| Open gate | Full width and full height | Maximum | Largest files, slower readout |
| 16:9 full width | Full width, reduced height | Full horizontal | Discards top and bottom |
| Oversampled 4K | Large area downscaled | Wide | Better detail, fixed shape |
| Crop mode | Central region only | Narrower | Faster readout, smaller look |
| Anamorphic 4:3 mode | Taller central area | Depends on squeeze | Designed for 2x anamorphic |
The key difference from oversampling is purpose: oversampling improves detail within a fixed delivery shape, while open gate preserves extra picture area for decisions made later.
When to use open gate
Open gate is most useful when the final framing is not yet fixed or when lenses need the full sensor height. The decision table below summarizes typical situations.
| Situation | Benefit of open gate | Point to watch |
|---|---|---|
| Anamorphic lenses with 2x squeeze | Uses tall sensor area for a wide desqueezed image | Lens coverage and vignetting |
| Horizontal and vertical deliverables | Extract 16:9 and 9:16 from one take | Frame both versions on the monitor |
| Visual effects plates | Extra margin for tracking and stabilization | Higher storage per shot |
| Documentary with uncertain framing | Room to reframe in post-production | Readout skew on fast pans |
| High frame rate action | Often not suitable | Frame rate limits in full readout |
Limitations and common pitfalls
Open gate offers flexibility, but it shifts work and cost into post-production. Teams that choose it without planning often run into the following problems.
- Storage and transfer load rise sharply because each frame contains far more pixels than a 16:9 recording.
- Rolling shutter artifacts can increase when the full sensor height must be read.
- Lens coverage may be insufficient, causing dark corners because some lenses only cover the 16:9 area.
- Composition errors occur when operators frame for the whole open gate instead of the delivery frame lines.
- Pipeline compatibility requires editing and grading software that handles nonstandard frame sizes correctly.
The short version
Most video is shown as a wide rectangle, but camera sensors are usually a bit taller than that. Normally the camera throws away the top and bottom of what the sensor sees. Open gate means it keeps the whole picture instead.
That extra space lets editors decide later how to crop the image, for example making both a wide video and a tall phone video from the same recording.
Where it makes a difference
A brand video team films a product launch that must be delivered as a 16:9 film for a website and as 9:16 clips for phone screens. The camera operator records in full-frame open gate at 3:2 and uses a monitor overlay showing both frame lines, keeping the presenter inside the shared safe area.
In post-production, the editor extracts the widescreen version from the center of the frame and the vertical clips from the full sensor height. Because the vertical crop draws on the extra rows above and below, the phone versions keep usable resolution instead of becoming a narrow slice of a 16:9 image. One shoot delivers all required formats, at the cost of roughly 20 percent more pixels per frame than a full-width 16:9 recording.