Digital BW, The Print

> From: Jon Zax [mailto:lotus@...]
>
> While it's possible to get very similar results from using the curves
> dialogue and the levels dialogue, they are not the same and do not
> function the same.
>
> When you pull in the white point slider in the levels dialogue, you
> are clipping all the data above the slider.
>
> If you do not move the end points in the curves dialogue and increase
> the contrast,say, with a traditional "s" curve you are reassigning
> values in the
> image but not clipping any.
>
> There is a difference and curves is much less destructive than levels.

That's true. That's one of the things that you can do with Curves that you
can't do with Levels. Indeed, it's useful to bring up Levels, move the
endpoints inward to the edges of the histogram, note the numeric values,
cancel it, and then use those numbers as the starting point for the Curves
dialog. (Now that PSCS has full 16-bit support, there's no point.)

But if you do the same thing with Curves that you do with Levels, i.e., move
the endpoints inward, then you do indeed get the same results. I think there
was some speculation that the underlying Curves engine would somehow result
in less posterization or noise than Levels.

> That said, the notion that a combed histogram is bad is much too much
> overstated, and generally speaking the problems attributed to them
> arise from other issues.

The combing may manifest itself as posterization, in a quiet image. But in a
noisy image, the noise will drown out any posterization.

--

Ciao,               Paul D. DeRocco
Paul                mailto:pderocco@...