Re: Smear

Louis Boyd <boyd@xxxxxxxxxxxxxxxxxxxx> wrote:

Why do you think it's "contrary to transport direction"?

What I am trying to say is that the bright line should run in the opposing
direction.
All explanations I found say that smear happens during the vertical
transport phase. Either by continous exposure to light (Frame Transfer
CCDs without shutter) or by electrons spilling horizontally into the
vertical
shift register (Inter Line Transfer with shielded shift register).
Either way: at every step of vertical transfer the pixels next to the bright
spot in the picture "get brighter", right? That is why I think the resulting
briht line should only run from the bright spot to the border of the
picture.



The slow clocking of the entire picture in almost all video and still
cameras is in the vertical direction. When a spot is over exposed the
excess electrons spill along the transport direction both up and down.
During the exposure phase? Would that not be smear but blur?
Smear doesnt have anything to do with better isolation against horizontal
spilling, does it?


They are well isolated from spilling horizontally. The horizontal
clocking only takes place in one specialized readout line at high speed
on the vast majority of ccds. Since spilling has already taken place
and no additional electrons are being added there is very little
horizontal smear.

Smear isn't much of a problem on modern CCDs. Many ccd designs drain
off electrons in over saturated pixels rather than leaking them to
adjacent pixels. A bright spot on a ccd can also cause electrons to be
released in horizontally displaced pixels too from either from IR
transparency, internal reflection, or reflection off the package
window, but that doesn't involve electrons moving between pixels.
.

Relevant Pages

  • Re: Smear
    ... I am trying to uderstand the cause of smear in CCD-cameras. ... Since spilling has already taken place and no additional electrons are being added there is very little horizontal smear. ... Smear isn't much of a problem on modern CCDs. ... Many ccd designs drain off electrons in over saturated pixels rather than leaking them to adjacent pixels. ...
    (sci.optics)
  • Re: Any in-camera HDRs available?
    ... into adjacent pixels *before* the well is full. ... backlit, high quality, low defects 6.1x6.1cm sensor, ... and if you take one and a half minutes reading out the sensor ... you also get less than 5 electrons read noise. ...
    (rec.photo.digital.slr-systems)
  • Re: Why not make the sensor larger?
    ... The Janesick article does not state that readout times for individual CMOS pixels are huge. ... To get 96 db of dynamic range, ... enough photons: 65535*(read noise in electrons). ... So if read noise matched the current lowest read noise ...
    (rec.photo.digital)
  • Re: Talking to digital camera novices about choosing a camera.
    ... Lens quality ... 2a) Full well capacity in electrons ... Full Press Shutter lag ... misinterpreted as number of pixels. ...
    (rec.photo.digital)