Black and White Tweaking the black in the "levels" menu

  • Thread starter Thread starter InTheBowl
  • Start date Start date
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InTheBowl

Can someone explain to me why, when I use auto levels, or I tweak the black
point to the "left" end of the hump (like I was told to) I start to lose
separation in my blacks tones? Things like the darks of eyes and the corners
or mouths start to go to pitch black. BUT...if I ignore the advice of "auto"
levels and yank the black point further to the left (toward "0") I can start
seeing separation in peoples eyes again. If I were to believe the histogram
it says there is nothing there....yet there is?
 
Can someone explain to me why, when I use auto levels, or I tweak the black
point to the "left" end of the hump (like I was told to) I start to lose
separation in my blacks tones? Things like the darks of eyes and the corners
or mouths start to go to pitch black. BUT...if I ignore the advice of "auto"
levels and yank the black point further to the left (toward "0") I can start
seeing separation in peoples eyes again. If I were to believe the histogram
it says there is nothing there....yet there is?
Click to expand...


Are you comparing this on the video screen?
Look at the black test strip at the bottom of
http://www.scantips.com/basics11.html
to see if your monitor is showing (differentiating) the dark tones.
You may just need to increase the monitor controls.

Also, a different perspective, if you are using either Elements or Photoshop
Levels, then holding the keyboard ALT key down (Windows assumed) while moving
the black or white point slider, will show all the pixels that are being
clipped at the current level.
 
SNIP
BUT...if I ignore the advice of "auto" levels
Click to expand...

Auto Levels clips the Black/White points with a percentage you can set
in the Levels dialog. If you set the percentages to 0%, there can be
no clipping. In general, be careful with anything "Auto".
If I were to believe the histogram it says there is nothing there....
yet there is?
Click to expand...

When you hold the ALT/Option key while dragging the Black/White
markers in the Levels dialog, you can see where/when the clipping
starts, and you can decide how far you want to take it.

Bart
 
Wayne Fulton said:
Are you comparing this on the video screen?
Look at the black test strip at the bottom of
http://www.scantips.com/basics11.html
to see if your monitor is showing (differentiating) the dark tones.
You may just need to increase the monitor controls.

Also, a different perspective, if you are using either Elements or Photoshop
Levels, then holding the keyboard ALT key down (Windows assumed) while moving
the black or white point slider, will show all the pixels that are being
clipped at the current level.
Click to expand...
Alt Key. Great tip. Thanks Wayne. Yes I was looking at the results on
screen. PhotoShops levels often seem to show a "flat line" when the blacks
get down to a very small amount. My monitor was calibrated for brightness,
contrast and colour with OptiCal about a month ago so it's probably in the
ball park. The wedge on your page shows up as I imagine it should. The
problem I was having was definately not completely understanding the
clipping phenom' at the extremes. Thx again.
 
Bart van der Wolf said:
SNIP

Auto Levels clips the Black/White points with a percentage you can set
in the Levels dialog. If you set the percentages to 0%, there can be
no clipping. In general, be careful with anything "Auto".


When you hold the ALT/Option key while dragging the Black/White
markers in the Levels dialog, you can see where/when the clipping
starts, and you can decide how far you want to take it.

Bart
Click to expand...
Thx Bart. I'll try tweaking the percentage too and see it I can get it to an
acceptable level.
 
Bart van der Wolf said:
SNIP

Auto Levels clips the Black/White points with a percentage you can set
in the Levels dialog. If you set the percentages to 0%, there can be
no clipping. In general, be careful with anything "Auto".


When you hold the ALT/Option key while dragging the Black/White
markers in the Levels dialog, you can see where/when the clipping
starts, and you can decide how far you want to take it.

Bart
Click to expand...
Are you talking about VueScan or PhotoShop. What happens if I tweak the
exposure clipping in VueScan?
 
SNIPPED
Are you talking about VueScan or PhotoShop. What happens if I tweak
the exposure clipping in VueScan?
Click to expand...

I assumed you were talking about Photoshop. I did.

The exposure clipping setting in VueScan only needs to changed from
its default in special cases (where you want to optimize the last bit
of scan exposure). The setting adjusts the heuristics used by VueScan
to maximize the exposure time with minimal or no clipping of the most
transparent areas in the crop area.

Bart
 
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