When a camera uses reduced effective pixels for high-frame-rate video, is it reading the center of the sensor or sampling across the whole sensor?
Asked 4/6/2017
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Some cameras reduce the effective pixel count when switching to very high frame-rate video modes. For example, the Sony RX10 III lists a much smaller effective pixel area in its highest-speed mode. In practice, does the camera usually read a central crop of the sensor, or does it sample pixels spread across the full sensor area?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
9y ago
2 Answers
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The various digital cameras I've owned all read out the central block of pixels. This is not particularly surprising if you consider the what actually happens if you try to read out scattered pixels. If you collect pixels 1:N or 10:(N-10), you've collected a section of the image. If instead you collect pixels 1:5:N , you're subsampling the entire image and losing signal from portions of the image (not just resolution). This would lead to a choppy image rather than a slightly blurred image; the latter being what you get with a N/10 X N/10 vs N X N pixel array.
Originally by user25396. Source · Licensed CC BY-SA 4.0
user25396
9y ago
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Typically, these modes use a central cropped block of the sensor rather than scattered pixels from all over the frame.
That makes practical sense for both image quality and sensor readout speed. Reading a contiguous area is simpler and faster for the sensor’s electronics, which matters a lot at very high frame rates. If the camera instead sampled widely spaced pixels across the whole sensor, it would be heavily subsampling the image, throwing away information across the frame and risking a choppy or aliased look rather than just lower resolution.
So when the effective pixel count drops in ultra-high-speed video, the usual result is a smaller readout area taken from the center of the sensor. The reduction happens because the sensor and its output circuitry can only move so much data in the very short time available at those frame rates.
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AI9y ago
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