Create a
Levels adjustment layer, or reopen its window by double clicking
the Levels window thumbnail in the Levels adjustment layer.
Sliders Method
You can stretch the contrast range of a photograph by using the
three triangular sliders, located below the histogram, in the Levels
window.
When using the sliders, the histogram in the Levels window doesn't
change, but histogram in the palette bin does change.
Moving the Sliders
There are two ways you can move the black and white sliders:
1) By hand
2) Clipping point method
We'll look at those, and will end with how to use the gray slider.
By Hand
White Slider
If there's no
image information to the left of the white slider, move it to the
left, to the point where there's image information.
The above is not a rule.
If your photograph doesn't look good, don't slide as far.
Black Slider
If there's no
image information to the right of the black slider, move it to the
right, to the point where there's image information.
Again, if your photograph doesn't look good, don't slide as far.
Clipping Point Method
White Point
1) Press and
hold Alt, and then click the white triangular slider.
The photograph will turn black.
2) Gradually
move the slider to the left.
3) Release the
slider when the first white area of your photograph that reappears.
Note
If a white area appears immediately, after pressing and holding
Alt, and clicking on the white triangular slider, use a white area
that appears after moving the slider.
Black Point
1) Press and
hold Alt, and then click the black triangular slider.
The photograph will turn white.
2) Gradually
move the slider to the right.
3) Release the
slider when the first black area of your photograph that reappears.
Note
If a black area appears immediately, after pressing Alt and clicking
on the black triangular slider, use a black area that appears after
moving the slider.
Gray Slider
After setting
the black and white-point sliders, use the gray-point slider to
adjust the brightness of the photograph, if needed.
This slider is also called the contrast or gamma slider.
Move the gray-point
slider back-and-forth to change the contrast of your photograph.
Don't press and hold Alt, like you did above.
The Input Levels boxes above the histogram in the Levels window
show, respectively, from left to right:
• Black-point setting
• Gray-point setting, also called contrast or gamma
• White-point setting
1.00 is the default gray-point setting, in the middle.
If you move the gray-point slider to the left, contrast decreases.
The gray-point becomes larger than 1.0.
Move it to the right, contrast increases.
The gray-point becomes smaller than 1.0.
Using the Color Channels
You can also adjust the gray-point slider for each of the three
color channels.
Do this if the histograms of the color channels (use the histogram
in the palette bin) show that they're very different.
Here's the color channels histogram for the snow-covered pool
photograph.
There's little difference between each channel, so there's no
need to change each color channel.
Here's a photograph of a red picnic table.
It's color channel histogram shows, as you expect, very different
color channels.
The photograph may benefit if each color channel was optimized
individually.
Go to the Channel
box and select red, green, and blue.
Don't use the
gray-point slider until after you've adjusted each color with the
white and black-point sliders.
Then, switch
back to the RGB channel to adjust the contrast, with the gray-point
slider, if needed.
If an unwanted
color balance shift occurs, tweak the appropriate color channel
with the gray slider.
You probably will never use the Output Levels sliders at the
bottom of the Levels window.
Output Levels Sliders
There are also black and white sliders for output levels.
Slide them back-and-forth to change the tonal range of a photograph.
They're called output sliders because you use them to match a
photograph to the ability of a device or medium to reproduce the
photograph, such as newsprint.
