Re: Change exposure to adjust histograms or do in post



Floyd L. Davidson <floyd@xxxxxxxxxx> wrote:
Wolfgang Weisselberg <ozcvgtt02@xxxxxxxxxxxxxx> wrote:
Floyd L. Davidson <floyd@xxxxxxxxxx> wrote:
Leon@xxxxxxxxx wrote:

Why do you think the histogram has to be centered?

It's merely the count of pixels of different brightness levels... centering it
for no reason is stupid.

You do realize that using the in camera light meter
does, well... *exactly* that!

Nope. Average metering does that. Spot metering does that
ONLY with the selected spot. Weighted average metering
doesn't since it uses lower weights on the borders.

So yes, it *does* exactly that.

Nope. Counter example: middle gray image with white border,
each having the same area in the photo.
Average would center the histogram, i.e. :

| * * |
| * * |
| * * |
| * * |
+---+---+---+---+---+
1 2 3 4 5

Weighted Average prodces a lighter image, i.e. the histogram
is not centered, since the borders have less weight.

So, no, it doesn't center the histogramm. It centers only
the *weighted* values.

Please don't try to be pitpicking and pedantic.

Please don't use words like "*exactly*", then.

You can of course adjust the
light meter to use only part of the scene, and of course
it centers that part of the histogram.

That is spot or center metering, but not weighted average.

Matrix/evaluative metering looks the brightness pattern up in a
database and decides based on that; tricks like detecting "it's so
bright, it must be daylight and outside" and basing the metering
on that are also tools of it's trade.

And then it tries to "center" it!

Nope. If it detects e.g. a backlit situation, it does NOT center
the histogramm: it decenters it by allowing the true subject to
come closer to a good exposure --- however the database and the
camera maker define that --- and may ignore the clipping of the
backlit parts.

No centering there.

Additionally, if it detects "full sun light at high noon", it also
doesn't center it, but uses the "sunny 16" rule and compensates
from there --- no matter how deformed the histogramm may be.

No centering there either.

-Wolfgang
.