It's somewhat difficult to explain. I took a copy of your image and
tried to make a correction to illustrate what I'm seeing but the 8bit
grayscale is too fragile to produce the result I wanted.
What I see in your photo is a grayscale rendering which has an
inverted inflection point in it. That is..if you were to take a
rectangle and fill it with a simple gray gradient from white to
black, you'll see a linear gray gradient. If you then select half the
area of that rectangle and create a new adjustment layer with a
Curves tool adjustment, create a gentle S-bend ... Now you will see
the gamma curve steepen, the area covered by the adjustment goes to
black and white faster from the midpoint. If you then select the
other half of the rectangle, create another adjustment layer but this
time instead of a gentle S-bend curve you fit an S-bend where the
left inflection point is slightly higher than the right inflection,
you'll see the gradient cycle from black to white to black to white
across the rectangle.
The result with an image like your pooch is that areas that should go
in an even slope from gray to black go very flat .. many levels of
differentiation between grays are lost, and the effect to my eye is
of mid-tones becoming "squashed" together. The right correction is to
go back to the original data and work up again from raw, starting
with white point and then black point clipping, and then work the
curves gently to express all the gray tonalities such that the curve
shows a smooth transition from black to white no matter what part of
the image you select and look at the histogram.
I'm not explaining this very well. I'll think about it over night and
see if I can come up with an improved explanation.
Godfrey
On Oct 17, 2005, at 12:01 AM, Shel Belinkoff wrote:
Please explain and be a bit more specific ... thanks!
Shel
[Original Message]
From: Godfrey DiGiorgi
http://home.earthlink.net/~scbelinkoff/pooch.html
The rendering is a little funny: some of the mid-tone grays seem a
bit squashed
