What is sensor readout speed?
Sensor readout speed is how fast the camera can read and transfer all the pixel data from the sensor after an exposure. Faster readout means less rolling shutter distortion, higher burst rates, and smoother video — it is one of the most important specs in modern cameras.
Why readout speed matters
The sensor reads image data line by line, from top to bottom. If this process is slow, fast-moving subjects appear distorted — this is the rolling shutter effect. Faster readout reduces or eliminates this.
Burst shooting: A faster readout means the camera can clear data off the sensor quicker and take the next shot sooner. This is why stacked sensors can shoot 30–120 frames per second.
Video quality: For 4K at 120fps, the sensor needs to read the entire frame 120 times per second. Slow readout means the camera has to crop or skip lines to keep up.
Flash sync: Faster readout enables higher electronic shutter flash sync speeds — critical for studio photographers.
What determines readout speed
Sensor architecture is the biggest factor. A standard BSI sensor reads at moderate speeds. A stacked sensor with built-in DRAM reads dramatically faster because data is buffered on-chip.
The Sony A9 III uses a global shutter — every pixel is read simultaneously, not line-by-line. This eliminates rolling shutter entirely.
Image processor speed also matters. Even a fast sensor needs a powerful processor to handle the data throughput.