The purpose of anchor points is to allow us to adjust tone by reshaping the
curve. By placing anchors on the curve and then moving the anchors, we
change the relationship between the input tones and the output tones. We
can also use anchors to lock part of the curve so when we make a change in one
part of the curve the rest of the curve does not change.
Adobe Photoshop automatically includes anchors for the black and white
points. In addition, we can add up to 14 additional anchor points of our
choosing for a total of 16 points.
Figure 1. Use anchors to
reshape the curve. Mouse over, or click, to see the actual adjustment.
Figure 1 shows an example of reshaping the curve using two anchor points.
One anchor point was added at tone 64 and another anchor was added to tone 192.
Tone 64 is the tone of the dark gray chip on the left and tone 192 is the tone
of the light gray chip on the right. For this particular example, the tone
of the dark gray chip was raised to 94 and the tone of the light gray chip was
lowered to 162. This should lighten the dark gray chip and darken the
light gray chip. Mouse over Figure 1 to see the result. As the red
arrows show, the tones between the dark and light gray chips became closer.
Therefore, the contrast between the two has decreased.
To add an anchor to a curve, click on the curve. If the anchor is not
exactly where needed, use the Left/Right arrow keys to change the Input tone
value and use the Up/Down arrow keys to change the Output tone value in
increments of two. If the Shift key is pressed while using the arrow keys,
tone changes by increments of fifteen. If we click in either the Input or
Output boxes first, the arrow keys increment by one and Shift + arrow keys
increment by ten.
In practice, I find it easier to click on the curve to
initially place an anchor point. Then I click in the Input box to fine
tune the placement of the anchor point on the curve. Finally, I click
in the Output box to make my actual tonal adjustment.
We can add an anchor to the composite channel's curve or to an individual
channel's curve based on the image tone itself. First, change the Channel
drop down box on the Curves dialog box to the desired channel. Inside the
image, Ctrl + click + hold (Command + click + hold) the left mouse button and drag
over the image. When the desired location is found, release the left mouse
button. This will place an anchor on the selected channel's curve.
Even though it is not necessary to continue to press the Ctrl (Command) key
while dragging, it is necessary for the Ctrl (Command) key to be held down while
Or, Ctrl + click (Command + click) the area of the image. This is
the same as the preceding paragraph, but it removes the option of dragging over
To delete an anchor, click and hold the anchor and drag it out of the grid.
As we drag, the curve will reshape itself. But once we drag the anchor out
of the grid, the curve will snap back to the appropriate shape.
Or, activate the anchor and press the Delete key.
With the Curves dialog box open, hold down the Ctrl (Command) key and press the
Tab key. Photoshop will activate an anchor. An anchor is activated
when its circle becomes solid black. As we continue to Ctrl + Tab (Command
+ Tab), Photoshop will deactivate the current anchor and activate the next
anchor. Photoshop will cycle through the anchors from black to white.
If we Shift + Ctrl + Tab (Shift + Command + Tab), Photoshop will cycle through
the anchors from white to black.
Figure 2. Use anchors to
prevent the curve from changing. Mouse over, or click, to see the locking anchor
Both Levels and Curves are non-linear adjustments. This means the closer a
pixel is to the change the more it will be affected and the further away it is
the less it will be affected. When we use Levels we cannot isolate the
nearby pixels from the change. We can with Curves.
In Figure 2, an anchor was placed on tone 192, which is the tone of the light
gray chip on the left. The Output value for this anchor was changed to
128, which is a mid tone. The middle chip originally had a tone of 128,
but when we made the adjustment, the entire curve was reshaped. In order
to isolate this change from the rest of the curve, additional anchor points were
placed on the curve and
not changed. By not changing these additional points, they anchored
the curve in place. Mouse over Figure 2 to see the additional anchor
Did you notice that the middle and right chips are now the same tone? This
is because we were able to change the right chip's tone to 128 and keep the
middle chip's tone 128 by using additional anchors to isolate the change.
Table 1. Curve Dialog Box Shortcuts
|Add an anchor point
||Click on the curve. Use the arrow keys or the Input box to fine
tune its position.
|Add an anchor to the specified channel for a specific area of the
||Change the Channel drop down box on the Curves dialog box to the
desired channel. Inside the image, Ctrl + click + hold (Command
click + hold ) the left mouse button and drag over the image. When the
desired location is found, release the left mouse button. Even though
the Ctrl (Command) key does not have to be pressed down the entire time,
it does have to be pressed before click-holding the left mouse button
and the left mouse button has to be pressed while dragging over the
Or, Ctrl + click (Command + click) the area of the image. Similar as
above, but removes the option of dragging over the image.
|Add an anchor to each individual color channel, but not to the
composite channel, for a specific area of the image
||Ctrl + Shift + click (Command + Shift + click) the area of the image
|Select one or more anchors
||Shift + click the anchor(s)
|Cycle through the anchors
||Ctrl + Tab (Command + Tab) to cycle through the anchors. The active
anchor will be solid black.
|Deselect all anchors
||Ctrl + D (Command + D)
|Change the Input value of the active anchor
||Left/Right arrow keys.
Or, click in the Input box and use the Up/Down arrow keys.
|Change the Output value of the active anchor
||Up/Down arrow keys.
Or, click in the Output box and use the Up/Down arrow keys.
|Delete an anchor point
||Ctrl + click (Command + click) the anchor.
Or, activate the anchor and press the Delete key.
Or, click and drag the anchor off the grid.
|Remove all anchors and adjustments
||Alt + click (Option + click) the Cancel button. The black and white
point anchors will not be removed, but they will be repositioned to 0
and 255 respectfully.
|See where part of the image falls on the curve
||Click and hold the mouse button over the image area. A clear ball
will appear on the curve showing the location of that area on the
curve. If the mouse is moved around the image while holding down the
left mouse button, the ball will move along the curve showing the
location of the area the mouse is currently over.
|Draw straight line with pencil tool
||Once the pencil tool is active, click in the grid, move the pencil
and then Shift + click to complete the line. After drawing several
lines, the lines can be connected by clicking the Smooth button.