Gamma adjustment and exposure compensation

Any relationship here between the 2? Can you say a gamma adj to 1.5 is 
the same as exp compensation of 1.5?

Hi Jeff,

> Can you say a gamma adj to 1.5 is the same as exp compensation of 1.5?

I believe the answer is No. The Input ends of the histogram have to be
adjusted in addition to gamma if you want to make a true exposure
compensation.

You may be interested in the post I made in the PPX3 newsgroup,
"Correcting
under-exposure" 04/02/07.

Regards

Gareth

Hi Chris,

> Increasing exposure will increase all the image shadows, midtones and 
> highlights proportionally. If the whole picture is dark then inctease the 
> exposure.

When you say increase exposure which image adjustment tool do you mean?

Is there a specific tool in version11 which I would not see in my version 
10?

Regards

Gareth 

I'm no expert, but the graphs on the contrast enhancement tool help me to 
understand the relationship. Gamma helps to increase the brightness of the 
midtones a lot while increasing the highlights much less. eg if the faces in 
a picture are dark but the background sky is bright you are better off 
adjusting gamma rather than overall exposure.

Increasing exposure will increase all the image shadows, midtones and 
highlights proportionally. If the whole picture is dark then inctease the 
exposure. Always save an original copy of the image for back up.

Kind Regards
Chris

"jeffkrol" <jeffkrol@ameritech.net> wrote in message 
news:460b0d29$1_2@cnews...
>
> Any relationship here between the 2? Can you say a gamma adj to 1.5 is the

> same as exp compensation of 1.5?
> 

Thanks Chris,

Ah, I understand. When you said "increasing exposure" you were
referring to
the brightness adjustment. I shall have to disagree with you slightly there:
I do not believe brightness is the same as exposure.

I carried out a series of tests on exposure (which I mentioned in the thread
which I drew to Jeff's attention). I photographed a colour chart (though any
static subject would have served almost as well). I took one picture at the
correct exposure, then a series purposely over-exposed and under exposed in
increments of 1/3 of a stop.

The task I set myself was to make the incorrectly exposed photographs match
the correctly exposed one as closely as possible. I copied a section of the
correctly exposed image and placed it on top of each incorrect image as a
new object. This way I could see exactly how close I was getting with my
adjustments.This is what I mean by "exposure compensation". I believe
some
RAW converters do exactly this with their "exposure" adjustments - it
is not
the same as B/C/I or Gamma.

The best single solution I found was to use the contrast enhancement, but
the input sliders have to be adjusted with as much care as the gamma slider.
An added refinement is to adjust the colour saturations in various ways, but
this is really only necessary when the exposure is off by several stops.

I ended up with a series of corrections which I could write down and use on
other images which I thought were incorrectly exposed. This reduces the
guesswork involved to a very large degree.

Of course I am talking about very precise work here, not necessarily
everyone's cup of tea! However I still think is probably the answer to
Jeff's question.

Sounds as if you are enjoying discovering more and more about this digital
business. I am continually trying to claw my way up too!

Regards
Gareth