On Monday, April 07, 2008 at 9:06, Carel wrote:
> Quote from the wiki article:
> "...To determine this point draw up and down the exposure slider. There is a
> point where lowering the exposure does not further decrease the size of the
> clipped area (a grey wedge would be better here). You can verify the setting
> with the next darker images. Don't forget to press Select All before you make
> any adjustments."
> I have followed this advise for a long time, but often ended up with a
> completely desaturated (grey) area around the sun when lowering the exposure
> that way. I am guessing the desaturation happens because ACR does some
> histogram "healing" in the background and when the exposure is reduced it
> reveals the area where the info in the blue channel was missing...?
Yes, this seems due to ACR highlights recovery.
The above described procedure is intended to *determine* the correct
parameters you need to extract the complete dynamic range. It is not
intended to actually use it on real world images.
And of course you have to look at the images. If an actually
overexposed area turns grey this is certainly no increase in dynamic
The advice "There is a point where lowering the exposure does not
further decrease the size of the clipped area" was meant as a help to
find the point where lowering the exposure gives no increase in
dynamic range on the highlights side - the area stays clipped (by
sensor in this case, not by ACR) no matter whether it is grey or