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Sensor line readout process
  • joetheprojoethepro

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    Looking at something like this sensor readout table for an x-h2s from dpreview, I was trying to understand how one would interpolate to find the readout speed for 1080p240. The 240p on this camera is exceedingly soft, supposedly because of the sensor resolution and needing more lines to be skipped because there is not enough speed available to do a full pixel readout even at the 1.38x extra crop.

    So when we talk about reading the sensor lines, does it read the lines pixel by pixel, or somehow read the entire line in one instance?

    I had initially assumed it was pixel by pixel across each line. In this thinking I was looking at the relationship between rez and timing, which definitely doesn't appear to be linear (6.2k --> UHD 4K is 3x MP drop but only 20% speed increase). But when considering lines vs MP, for each doubling in lines there is a 4x increase in resolution. So depending on if these readouts are based on total res or just number of lines will definitely affect those calculations.

  • 2 Replies sorted by
  • Vitaliy_KiselevVitaliy_Kiselev

    only CCD is being read by shifting and pixel by pixel. CMOS can be read very differently, depends on sensor design.

  • EspenBEspenB

    Basically sensors now use line-skipping and/or pixel binning to increase speed for HFR modes. Croppping is the last resort, but maybe to avoid the other two methods listed, in favour of a sensor crop to offer 1:1 pixel read out instead. I would guess even binning could be followed by a down sampling (scaling) to provide a standard resolution output from the camera. So perfect timing calculations based on binning etc might not give true results.

    Back in the glorious Canon 5DM3 days, line skipping was used even at ordinary frame rates since the high megaixel sensor could not be read out fast enough for video.

    https://en.wikipedia.org/wiki/Pixel_binning

    I.e. IMX677 from Sony famously used by i.e. GoPro Hero 9 and 10, it delivers:

    2799 x 1405 pixels in 10-bit HFR mode (261 fps max), which is completely non standard and need to be downsamplet to i.e. HD resolution.

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