ufraw -- exposure vs base curve

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ufraw -- exposure vs base curve

Gary Aitken-2
Hi Folks,

Not sure where to ask this as I couldn't find a ufraw forum, but I
figured a number of users here might be able to answer.  Please
redirect me if this is inappropriate.

Can anyone explain to me the difference between manipulating the
base curve in ufraw and boosting the exposure?  I'm wondering in
terms of where in the processing pipeline the change takes place.
i.e. If I could manipulate the base curve to make the image look
exactly the same (to my eye, I know it's not perfect) as boosting
the exposure, is there fundamentally a difference in the result?

Thanks,

Gary
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Re: ufraw -- exposure vs base curve

Rick Strong-2
Hi Gary,

If you are talking about photographs, altering the curve is not the same as
boosting the exposure.

Generally speaking, boosting the exposure makes the whole picture brighter,
while playing with the curve alters areas--shadows, mid-range,
highlights--of the photograph. But, you may play around with one to end up
with a result very similar to the other. This is best done in raw.

Rick S.

-----Original Message-----
From: Gary Aitken
Sent: Wednesday, March 14, 2018 1:45 AM
To: [hidden email]
Subject: [Gimp-user] ufraw -- exposure vs base curve

Hi Folks,

Not sure where to ask this as I couldn't find a ufraw forum, but I
figured a number of users here might be able to answer.  Please
redirect me if this is inappropriate.

Can anyone explain to me the difference between manipulating the
base curve in ufraw and boosting the exposure?  I'm wondering in
terms of where in the processing pipeline the change takes place.
i.e. If I could manipulate the base curve to make the image look
exactly the same (to my eye, I know it's not perfect) as boosting
the exposure, is there fundamentally a difference in the result?

Thanks,

Gary
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Re: ufraw -- exposure vs base curve

Gary Aitken-2
On 03/14/18 12:51, Rick Strong wrote:

> If you are talking about photographs, altering the curve is not the
> same as boosting the exposure.
>
> Generally speaking, boosting the exposure makes the whole picture
> brighter, while playing with the curve alters areas--shadows,
> mid-range, highlights--of the photograph. But, you may play around
> with one to end up with a result very similar to the other. This is
> best done in raw.

I understand altering different parts of the curve affects different
aspects of the image, e.g. highlights vs midtones vs shadows.  What
I'm asking is if modifications to exposure and the base curve are applied
to the same thing at the same place in the pipeline.

For example, I am looking at an image where with 0 exposure and the
default linear (45 deg lower left to upper right) base curve,
the rightmost 3/8 of the histogram is empty.  It takes an increase in
exposure of about 1.33 to bring the curve to the far right.  I can
get what appears to be the same effect by grabbing the upper right
anchor of the line and dragging it left until it is about 3/8 of the
way from the vertical left axis, essentially just making the slope of
the line a lot steeper and leaving the origin at the lower left.

Are those equivalent operations, or are they doing something subtly
different in terms of what processing is done to the image?  They
appear to be equivalent.  But that may not be the case.  For
example, does boosting the exposure affect noise or bayer decoding
artifacts more than adjusting the curve?

Alterations to the base curve in ufraw are applied at one point in
the pipeline and alterations to the secondary curve (under "Correct
luminosity, saturation") tab are applied at a different point.
Changes to the secondary curve affect the image in a different
manner than the exposure and the base curve.

Thanks,

Gary

> Not sure where to ask this as I couldn't find a ufraw forum, but I
> figured a number of users here might be able to answer.  Please
> redirect me if this is inappropriate.
>
> Can anyone explain to me the difference between manipulating the base
> curve in ufraw and boosting the exposure?  I'm wondering in terms of
> where in the processing pipeline the change takes place. i.e. If I
> could manipulate the base curve to make the image look exactly the
> same (to my eye, I know it's not perfect) as boosting the exposure,
> is there fundamentally a difference in the result?
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