Black holes in video mode

Started Dec 12, 2008 | Discussions thread
Thomas Nilsson
Contributing MemberPosts: 529
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Re: Applied's explanation makes sense
In reply to Berg Na, Dec 14, 2008

Hi

I almost agree fully.

Let's say that the reference level is in nomal condition at a zero level, and a fully white pixel att 100 level. When saturation begin to occur, the reference level is raised above 0-level, but does not necessarily immediately become equal or greater than the saturated pixel at 100-level. It's this region from zero level up to full saturation that will cause the grey area pixels.

Technically those pixels are very much affected by the raise of the reference level, as the result of the CDS will decrease. If the reference is half way up to the saturated signal level, the resulting output will be 50% grey.

Berg Na wrote:
The output level of a pixel is obtained by subtracting the reference
level from the signal level. This operation is called 'correlated
double sampling' or CDS, and it is performed to eliminate the noise
in the reset operation.
The black sun issue is observed when the reference data is saturated
by an unusually bright light source causing the reference level to be
equal to or greater than the saturated pixel. This results in an
output level of zero or black.
If the reference is near saturation, but not completely saturated,
then the output will not be completely black. Technically, these
pixels are not affected by the black sun effect.

Thomas Nilsson wrote:

Well, if you take a good look at the pictures I mentioned, you will
see the gradual transition.

It also makes sense from a physical point of view, the reference
level isn't a digital 0-1 level, it is an analog voltage potential.
The way the black holes appear in the video, makes perfect sense with
the gradual transition and the explanation of applied...

Correct me if I am wrong, but then also please explain the physics
behind it to make it happen like you say.
The consequence, if it is like you say, is that the 5DII problem in
that case is not the black sun problem, because the pictures I
checked have gradual transition from white to black.

It would be interesting to see the same scene, causing this problem,
shot with a number of different lenses.

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