I think our difference on the notion of "overall lightening/
darkening" is simple: I consider white clip and black clip to be
fixed in such adjustment, where you change the bias of the whole
curve. Fair point, but I'm comfortable with my approach .... I
consider white and black clip to be independent.
Gamma correction is, however, the relative shape of the slope between
white and black clip points so I differ with your interpretation
there. In that sense, all three of these are gamma corrections of a
sort, but I pick the two-node curve as being a "typical" gamma
correction where the single node corrections are more simplistically
used for overall light/dark.
All these curves are somewhat exaggerated to show the effect clearly,
of course. If exposure is correct, real adjustments would be
significantly smaller.
Of course, part of the reason to post the curves and their effects on
a gray gradient as well as a photo is to show what I meant, which I
struggle with in words. So consider them as examples of typical
curves in the Curves Adjustment tool and their effect on image
characteristic, regardless of the adjective used to describe what
kind of correction they represent... ;-)
(Boris, the pages will be there ... I rarely dump stuff until I run
out of space, and then usually in the "oldest first" order.)
Godfrey
On Oct 18, 2005, at 3:47 AM, Paul Stenquist wrote:
A good illustration. However, I wouldn't say that 02 and 03 are
"overall" lightening and darkening curves. The end points remain
fixed. They are midrange lightening and darkening curves. Because
the ends are ffixed, the brightest highlights and deepest shadows
remain unchanged. Rather than calling 04 a "gamma correction
curve," which cold be anything, I would describe it as a curve
intended to increase midrange contrast. Once again, the ends are
fixed.
On Oct 18, 2005, at 12:04 AM, Boris Liberman wrote:
Great many thanks... I will try to keep in mind the word "beer" if
we get to meet in person. Please don't remove that page from your
web site, will you?
- Boris, all is revealed at
http://homepage.mac.com/godders/grayscale20051017/
