Extra Pixels

Discussion in 'Image Processing' started by Brian Beezley, Feb 2, 2014.

  1. Brian Beezley

    Brian Beezley Mu-43 All-Pro



    I processed the top photo with Olympus Viewer 3. I noticed that I had aimed my E-PL2 too low and missed the top of the football. I loaded the .ORF into RawTherapee to check something. To my surprise, the football was complete! I seem to remember reading in the RT documentation that the program decodes all sensor pixels, not just those intended for the final image. Presumably for Olympus this means the pixels on each side that accommodate IBIS. For this particular image, I am grateful. OV3 lists the original image size as 4032 x 3024 pixels while RT has it as 4088 x 3076.

    Both images are cropped, but the top edge is the same as for the uncropped image. I didn't try hard to match gray tones.

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  2. RevBob

    RevBob Super Moderator Subscribing Member

    Jun 4, 2011
    NorthWestern PA
    Hmmm, interesting.
  3. Brian Beezley

    Brian Beezley Mu-43 All-Pro

    After a little poking around on the web, I think it may be DCRAW that provides the extra pixels, which are known as border pixels. DCRAW is the RAW converter that RawTherapee uses. The extra pixels may be intended for lens distortion compensation as well as IBIS.

  4. mattia

    mattia Mu-43 Hall of Famer

    May 3, 2012
    The Netherlands
    My guess is that they're the pixels 'removed' by lens distortion correction. You see similar effects in DxO by turning off the lens correction module.
  5. mfj197

    mfj197 Mu-43 Regular

    Aug 20, 2012
    Guildford, UK
    Yes, I think they are for lens correction. I don't think they are for IBIS though. Some forms of video stabilisation use extra pixels on the sensor by recognising when the entire image has moved on the sensor and capturing the next frame with the required offset, i.e. without moving the sensor at all. However IBIS purely moves the sensor itself in response to movement of the camera body detected by gyroscopic sensors.
  6. Ulfric M Douglas

    Ulfric M Douglas Mu-43 Hall of Famer

    Mar 6, 2010
    Good to know : for those one in a thousand top of the ball crises.
    I will remember this.
  7. Brian Beezley

    Brian Beezley Mu-43 All-Pro

    Ah, I'm sure you're right. Somehow I forgot that IBIS uses physical sensor movement during the exposure, not electronic correction. The camera can't read the pixels fast enough to do electronic correction on the fly. If it could, you could implement IBIS with no moving parts by using a larger sensor, such as APS-C.

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