writes:

Timo Autiokari wrote:
Exposure adjustment in fact is a linear
operation, multiplication by a factor,

Incorrect. It's scaled in F-stops, which are exponential, not linear.

Exposure adjustment by +1 fstop is the same as multiplication of the
data values by 2. Exposure adjustment by +2 fstop is the same as
multiplication of the data values by 4. So a linear operation. Just
the gradation of the aperture and the time dial is logarithmic, they
both affect to the data linearly.

You failed maths at school, didn't you?

Actually, Timo's right here.

"Linear" is a term that appears all over the place, with somewhat
different meanings. In high school math, linear probably refers to a
first-degree polynomial.

In signal processing, a linear system is one where the result of
applying the system to the sum of two signals is the same as the sum of
applying the system to the two signals individually (superposition).
(These are not the same; the function y = 2x + 3 is a linear
polynomial, but it's *not* linear in the signal processing sense).

And in television, the electronics are linear even though the signal
being processed is non-linearly related to scene brightness.

In this example, exposure adjustment is a linear operator in the signal
processing sense. The amount of adjustment can be specified directly
(2X, 0.5X), or as an equivalent number of stops. F-stops are a
logarithmic scale used to specify (in this case) a linear transformation
scale factor.

You'll find the mathematical details in
any good textbook onphotography.

Then study them.

I have. You clearly havn't.
I won't waste my time trying to educate you, as you clearly prefer to be
ignorant.

You're both arguing past each other, unable to see that each is applying
"linear" to something different.

Dave