I know that in CMOS sensor, the exposure is perform in line by line. I can assume that the delay between the exposure of two consecutive lines is equal the readout time for one line. So the readout time for the entire frame is

Frame_readout = line_readout * number_of_line

I read in many articles in the Internet that the interval between frames is qual the frame readout time. So the frame rate is calculated as

Frame_rate = 1/frame_readout

Therefore I assume that the delay between exposure of the last line of the 1st frame and the first line of the 2nd frame is equal the readout time for one line. It means that exposure in the sensor occurs from the first line to the last line and then come back to the first line (for next frame) and so on. And the delay between the exposures of two consecutive lines are always the same, whether these two exposures belong to the same frame or not.

Is my assumption correct? If not, what does contribute more delay for the exposure of the first line of the next frame? And what is the frame rate in that case?

enter image description here

  • Your analysis is oversimplified somewhat. You also need to take into account the shutter speed (either in fractions of a second, or in degrees if you're into that). I also get the feeling that over a given frame rate, there may be multiple scans of the sensor that are composited to create a "frame" of video that gets encoded and stored. But that is conjecture on my part.
    – WineSoaked
    Commented Aug 10, 2015 at 6:12
  • Hi @WineSoaked, I did take into account the shutter speed, which was indicated as "exposure" in my figure. Of course in this case the shutter speed is short than the frame interval.
    – opmfan
    Commented Aug 10, 2015 at 7:26

1 Answer 1


Between frame is frame gap. In there, camera don't expose and coresponse it can not receive data at frame gap. And i think, frame_readout include frame gap (time between frame adjacent)

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