Adjust the color, tone and alpha channels with the curves adjustment, either on individual channels or by adjusting the master curve.
Curve reset
Inverted S Curve
S Curve
In the images above, the effects of a default reset curve, an inverted "S" curve and an "S" curve are presented. As shown, the inverted "S" curve type can be used to reveal more detail in the shadows whilst protecting the highlights. The "S" curve, on the other hand, is typically used to obtain better control over image contrast while delivering deeper shadows and brighter highlights.
You can use the Curves adjustment to manipulate individual color channels. The adjustment can be used on placed images as well.
Settings
Apply this adjustment via the Adjustments panel using the following settings:
Color space—select a color mode (Grey/RGB/CMYK/LAB) from the pop-up menu.
Channels—specify a single color channel to apply the adjustment to, including the layer's alpha channel. Master (default) applies the adjustment to all color channels, excluding alpha channel.
Spline—displays the spline graph which can be shaped to adjust the image's tonal range.
Min and Max are the input minimums and input maximums and let you determine the range/threshold of values that are affected by the adjustment. They use a normalized 0-1 range (regardless of bit depth) but setting Max to >1 allows for the adjustment to manipulate HDR values as well. They can be also be used to fine-tune the manipulated tonal range in 8-bit and 16-bit documents.
Opacity—sets the level of visibility of the Curves adjustment.
Merge down—merges the Curve adjustment layer with the ones below it.
Reset—reverts the spline graph to its default position.
Delete—deletes the Curves adjustment and its layer from the panel.
Additionally, the following are available on the Spline dialog:
Linear—converts the curve to straight lines.
X—accurately positions any added and currently selected node on the X-axis of the graph. Use for precision in 32-bit linear workflows.
Y—accurately positions any added and currently selected node on the Y-axis of the graph. Use for precision in 32-bit linear workflows.
About curves
Curves can be used as a powerful alternative to controlling the brightness and contrast of your images. Depending on the position of nodes on the curve, various luminance levels can be achieved. The Curves graph is divided into three distinct areas responsible for:
the shadows (dark tones) on the left.
the midtones in the center.
the highlights on the right-hand side.
When the curve is lifted up, the area of the image affected will increase in its luminance value making those regions brighter. When pulled down, the luminance value will decrease thus making those areas darker.
From left: Curves adjustments affecting highlights, shadows, and midtones, respectively.To adjust a curves graph:
After tapping the Spline graph in the dialog, do any of the following:
Drag a node on the curve to adjust the tonal range of the image.
Tap on the curve to add additional nodes.
Tap to select an existing node and drag to manipulate it.
