Source：Shenzhen Kai Mo Rui Electronic Technology Co. LTD2026-05-09
What Is Shutter？
Global exposure and rolling exposure are two common exposure modes for cameras. Generally speaking, CCD cameras adopt global shutter, while most CMOS cameras use rolling shutter. So which one is better? Or more precisely, what are the essential differences between them? Let’s start with their basic definitions.
A shutter is a core camera component that controls the effective exposure time of the photosensitive sensor. It is an indispensable part of a camera. The structure, form and performance of the shutter are key factors that determine a camera’s grade. As a rule, the wider the shutter speed range, the better.
Shorter shutter speeds are ideal for capturing moving subjects. When shooting night traffic trails or light painting photography, a slower shutter speed is required. Similarly, the silky smooth water effect commonly seen in photos can only be achieved by using a slow shutter speed.
Rolling Shutter vs Global Shutter
Rolling ShutterRolling shutter is commonly implemented by row-by-row exposure on CMOS sensors.When exposure starts, the sensor scans and exposes row by row until all pixel points are exposed. All processes are completed in an extremely short time, and pixels in different rows have different exposure timings.
Global ShutterGlobal shutter exposes the entire scene at the exact same moment.All pixels of the sensor collect light and start exposure simultaneously.At the start of exposure, the sensor begins light collection; at the end of exposure, the light collection circuit is cut off. The sensor then outputs a complete image.CCD cameras work in the global shutter mode, with all pixels exposed at the same time.
For camera manufacturers, rolling shutter can achieve a higher frame rate. However, in cases of improper exposure or fast-moving objects, images captured by rolling shutter will deviate from what the human eye actually sees.
Generally speaking, CCD sensors mostly adopt global shutter, while CMOS sensors mostly use rolling shutter. When manufacturers select a shutter mode for a sensor, they need to take many factors into account, such as processing speed, power consumption, manufacturing cost, and overall structural complexity.
For static photography, the difference rarely matters. However, when shooting video, the choice of shutter type becomes crucial, especially when capturing high‑speed moving objects.
Why Does the Rolling Shutter Effect Occur?
For most cameras, the rolling scan speed is about 1/30 second. For ordinary moving objects, distortion is barely noticeable. But when shooting high‑speed subjects such as aircraft propellers, the rolling shutter effect becomes extremely obvious.
Capturing fast‑moving objects is not the only scenario where this artifact appears. When you take photos from inside a high‑speed moving car through the window, the rolling shutter effect will also occur. The following simulates the effect on a 10×10 pixel sensor.
This also explains why trees outside the window appear slanted when photographed from a high‑speed bullet train.
Interesting Creative Effects
Rolling shutter is not entirely a disadvantage. Although the rolling shutter artifact is usually undesirable, it can also be intentionally used to create unique and interesting photographic effects.
Global Exposure
The principle of global exposure is straightforward. Once the aperture opens, the entire image sensor is exposed simultaneously. Therefore, the exposure time is restricted by the mechanical opening and closing speed. Due to mechanical limitations, there is a theoretical minimum exposure time.
Advantages:All pixels are exposed at the same time.
Disadvantages:Exposure time is limited, restricted by the mechanical minimum shutter speed.
Rolling Exposure
As the name implies, rolling shutter works in a way similar to a rolling curtain. After the aperture opens, a moving virtual curtain with a variable gap controls the sensor’s exposure time. As shown in the diagram, the curtain scans from left to right.
The actual exposure duration is determined by the width of the curtain gap and its moving speed. The faster the curtain moves and the narrower the gap, the shorter the sensor exposure time. Thus, rolling shutter can achieve much shorter exposure times.
The motion principle is illustrated below: only the sensor area aligned with the curtain opening can receive light during scanning.
A certain position during the rolling curtain movement.
The next position of the rolling shutter during its movement
Advantages: It supports shorter exposure time.
Disadvantages: It works in row-by-row exposure mode, which causes smear artifacts and is not suitable for shooting moving objects.
Smear Artifact Analysis
Professional explanation:Smear is generated by the relative motion between the target object and the camera imaging system during exposure. This relative motion causes the image projected onto the sensor chip to change continuously. Pixels in different areas are affected by imaging information from different positions of the object throughout the exposure process. The final image is a superposition of frames captured within a continuously changing imaging space.
The image acquisition process of a camera actually consists of two stages:The first stage is exposure; the second stage is readout, in which data is read from the sensor registers and transmitted after exposure is completed.
When the camera captures the fast-moving Object A at Position 1, if the exposure time is too long, Object A will have already moved to a new position during exposure. As a result, the captured image is not purely the scene at Position 1, but a superposition of the original Position 1 image and slightly offset frames captured during the object’s movement, which creates smear artifacts.
A longer exposure time means a slower shooting speed, while a shorter exposure time reduces the amount of incoming light. In this case, it is necessary to open the aperture wider and increase supplementary lighting to ensure proper image brightness.
Therefore, when shooting moving objects, the exposure time must be set reasonably. Do not arbitrarily use an excessively long exposure time only for brighter images, as this will easily cause smear. If insufficient image brightness is caused by a short exposure time, compensate by widening the aperture and increasing ambient or auxiliary lighting.
Row-by-Row Exposure
The implementation of row-by-row exposure sensor is shown in the row-by-row exposure mode diagram. Unlike global exposure, row-by-row exposure starts from the first row; the second row begins exposure after one row period, and so on. After N−1 row periods, the N-th row starts exposure.
When the exposure of the first row ends, data readout begins. Reading out one row takes one row period (including the row blanking time). Once the first row is fully read out, the second row starts readout immediately, and the process continues sequentially. After the (N−1)-th row is read out, the N-th row begins readout until the entire frame image is completely read out.
Compared with global exposure sensors, row-by-row exposure sensors feature lower technical difficulty, lower cost and higher resolution, making them an ideal choice for static image shooting scenarios.
The implementation of a
global shutter sensor is illustrated in the figure.
All rows of the sensor start exposure simultaneously and end exposure at the same time. Once exposure is complete, the sensor transfers all photogenerated electrons from the photosensitive area to the storage area, and then reads out pixel data row by row.
The advantage of this exposure method is that every row in the captured image has a consistent exposure time. Moreover, no distortion, offset or skew will appear in the image when shooting moving objects.
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