The Levels control can be used to neutralize a
color cast. Two methods are discussed here. The first method
uses the eyedroppers on the Levels dialog box. The second uses the
individual color channels on the Levels dialog box. I find each method
easier to use if I first create light, dark and mid tone targets in the image.
Targeting these areas is discussed on the
Finding Lightest and Darkest Areas page.
Figure 1. Color image with a blue/cyan Cast
Figure 2. Levels Dialog Box
It is not uncommon for natural light color photographs to have a color cast
to them. This is not always bad. Sunrise/sunset photographs have a
most definite color cast. That is what makes these images so appealing.
However, sometimes a blue/cyan or magenta color cast can be seen in an image.
An example of such an image can be seen in Figure 1. The Levels adjustment
can be used to remove this color cast.
The first method to accomplish this uses the eyedropper tools. But the
eyedropper tools are most effective if the image has white and black areas and
an area whose color should be (but may not be in the original image) neutral.
If not, then we can use the second Levels technique to remove the color cast.
In Figure 2 can be seen the Levels dialog box. In the dialog box are three
eyedroppers. The purpose of the black eyedropper
is to take whatever part of the image it is clicked on and remap it to black.
The purpose of the white eyedropper
is to take whatever part of the image it is clicked on and remap it to white.
The gray eyedropper
behaves differently. It does not remap pixel tones to mid tone.
Instead, it takes whatever part of the image it is clicked on and neutralizes
its color while maintaining the original tone. Neutralizing a color means
making it gray, but not a mid tone gray. I have noticed that, except for
solid colors, the gray eyedropper does not absolutely neutralize a color.
Also, even when used on solid colors, I have noticed there is a slight shift in
tone, but usually ⅓ of a stop or less. However, this does not diminish the
usefulness of the Eyedropper technique.
Using the targeting techniques described on the
Finding Lightest and Darkest Areas page, I created the three Color Sampler
shown in Figure 1. Target #1 is a white area. Target #2, the shaded
side of the pine tree in the middle, is a dark area. Target #3, the pine
tree in the foreground, is a medium toned area whose color we want to be
neutral. We will be using all three eyedroppers to neutralize the color
Here are the steps I used to neutralize the color cast in Figure 1 using the
- Make sure the caps lock key is on. This will change the eyedropper
cursor to a crosshair
- Create a new adjustment layer. Layer > New Adjustment Layer > Levels.
- In the dialog box, click the white eyedropper
It is the eyedropper on the right.
- Place the eyedropper cursor over the image. When we do this, the cursor
will become a crosshair. This is the same crosshair used by the Color
- Position the eyedropper crosshair over the white target, in this case
#1. When the two crosshairs are perfectly aligned, they will merge and
- Click once using the left mouse button. Do not hold down
the Shift key while clicking.
- Repeat for the black eyedropper
using the black target, in this case #2.
- Repeat for the gray eyedropper
using the mid tone target, in this case #3.
The result can be seen in Figure 3. Figure 3 has had no other adjustments
other than the Levels eyedroppers. We can mouse over Figure 3 to see
The pine tree in the foreground now has a nice neutral color. The reds,
yellows, whites and greens are also true.
Figure 3. Color cast
removed with eyedroppers. Mouse over, or click, to see the uncorrected version.
The Color Channels technique is more involved but is used when we need
precise control. Even though Color Sampler targets
were not mandatory when using the eyedropper technique, they are necessary when
using the Color Channel technique.
Once the Color Sampler targets have been created, we will use the information
they provide to reduce the color cast. Where is this valuable information?
In the Adobe Photoshop Info panel. We can have up to four color sampler
targets in a Photoshop document. The image in Figure 1 has three.
They are labeled #1, #2 and #3, as shown in Figure 4. When the Levels
dialog box is open, the Info panel shows before and after tonal values for
each of the targets. The before values are on the left and the after
values are listed on the right.
In Figure 4, color sampler #1 has a red value of 201, a green value of 255
and a blue value of 254. Target #1 has a cyan cast to it because green and
blue are the dominant color channels and they are of similar amount (green +
blue = cyan). Color sampler #2 in Figure 4 has red and green values of 0
and a blue value of 15. Thus, target #2 has a blue tint to it.
Target #3, which is the bark of the pine tree, also has a cyan tint to it
because of the dominance of the green and blue channels.
When neutralizing a color cast, the intent is to change the RGB after values to
be identical to each other. For the white point (target #1), we want to
make each of the RGB after values equal to the highest RGB before value,
which is 255 in this case. For the black point, we want to make each of
the RGB after values equal to the lowest RGB before value, in this case
0. For target #3, we do not necessarily want to make the three channels
equal to each other, for this would make the tree bark a true gray. When
changing the image for target #3, we want to adjust it enough to leave some
color but not make it monochrome.
Figure 4. Info panel showing target information
Figure 5A. Red channel changes
Figure 5B. Green channel changes
Figure 5C. Blue channel changes
To remove the color cast using the Channels technique, follow these steps.
- Create a Levels adjustment layer. Layer > New Adjustment Layer >
- Using the Info panel, note the RGB values of the color sampler
targets. They are in the format before/after. The intent is to change the
RGB after values to be identical to each other for the black and white
targets. For the white point, we want to make each of the RGB after values
equal to the highest RGB before value. For the black point, we want to make
each of the RGB after values equal to the lowest RGB before value.
- To correct the white point. Using the Channel drop down box, select the
one or two channels, in turn, that do not have the highest RGB before
value. In this case, they are the red and blue channels (Figures 5A and
5C). Click in the right (white) Input Levels box in the Levels dialog box.
Using the down arrow key, change the number until the after value in the
Info panel matches the highest before value. In this example, we want to
change the value until the red channel 201 in the Info panel equals 255.
When we edit the blue channel we want to change the blue channel white point
value until the blue channel 254 equals 255. Looking at the three dialog
boxes in Figure 5, we note that the red channel white point was changed to
195. The green channel white point was not changed. The blue channel white
point was changed to 254.
- To correct the black point. Using the same Levels adjustment
layer, select the one or two channels, in turn, that do not have the lowest
RGB before value. In this case, it is the blue channel. Click in the left
(black) Input Levels box on the Levels dialog box. Using the up arrow key,
change the number until the after value in the Info panel matches the
lowest before value. In this example, we want to change the blue channel
until its after value in the Info panel equals 0. Referring to Figure 5
again, we note that the red channel black point was not changed. The green
channel black point was not changed either. The blue channel black point
was changed to 15.
- If further correction is still needed, then correct the mid point. This
change is more subjective than numerically precise. In this case we know
that the tree bark has a blue/cyan cast. To undo this dominance, we want to
change the values such that neither blue nor green + blue is dominant since
green + blue makes cyan. Therefore, I changed the values so that red and
red + green are dominant by changing the gamma value for each color
channel. Using the Channel drop down box, I selected each of the channels,
in turn. I clicked in the middle Input Levels box. Using the up/down arrow
keys, I changed the numbers until I got the desired effect. Referring to
Figure 5 once more, the red channel gamma point was changed to 1.23. The
green channel gamma point was changed to 0.91. The blue channel gamma point
was changed to 0.95.
When changing the mid tone target, it is important to
understand that as we change the red, green and blue channels, we are
changing the tone of this area. After we have made our changes, we can
use a Curves dialog box to check the mid tone target to see what the new
The corrected image can be seen in Figure 6. We
can mouse over Figure 6 to see corrected/uncorrected versions of the image.
Figure 7 shows the Info panel of the corrected image. Target #1 has been
neutralized to a true white. Target #2 has been neutralized to a true
black. Target #3 has not been neutralized, which is what we wanted.
But we eliminated the dominant blue/cyan color cast.
Figure 6. Color cast removed
with channels technique. Mouse over, or click, to see the uncorrected version.
Figure 7. Info panel of corrected image
For comparison purposes, lets see how the eyedropper and channels techniques
compare. In Figure 8 are the three Info panels. Figure 8A is the
Info panel for the uncorrected image. Figure 8B is the Info panel for
the image corrected by the Eyedropper technique. Figure 8C is the Info
panel of the image corrected by the Channels technique. (Figure 8C is
the same as Figure 7.)
Evaluating Figure 8A, we can tell the color cast was predominantly in the mid
tones since targets #1 and #2 (white and black areas respectfully) do not show
much deviation from neutral. Figure 8B shows that the Eyedropper technique
did a good job of neutralizing the blue/cyan cast in the mid tones (target #3).
It also did a good job of neutralizing the white and black points. The
Channels technique, Figure 8C, demonstrates the precise control this technique
allows. The whites and blacks were absolutely neutralized and the mid tone
area was changed as desired.
Figure 8A. Uncorrected Image
Figure 8B. Eyedropper Technique
Figure 8C. Channels Technique
The Channels technique can seem overwhelming to use. Therefore, a
suggested workflow for removing a color cast is as follows.
- First, locate white and black areas in the image that should be
corrected and use the white
eyedroppers and click these areas. If the results are unsatisfactory,...
- then locate a color in the image that should be neutral and is as close
to mid tone as possible. Use only the gray eyedropper
and click this area. If the results are still not satisfactory,...
- then use the Channels technique.
The key to using color correction is to be sure to
target the correct areas. Do not target deep shadows or