The Most Common Curves Adjustments

Curves

As an Epigraphic Survey artist who works almost exclusively with black-and-white images, one would think that learning about Photoshop’s color management is rather pointless. However, some of the Survey’s more recent documentation efforts (paint studies at Medinet Habu, Roman fresco project at Luxor temple) are strongly concerned with colors and tonal modifications. With one of Photoshop’s most powerful and flexible tools, called Curves, the artist is able precisely to control tones throughout an image. With Curves one can not only adjust the brightness of different parts of the tonal range, but also change individual color channels, correct color casts, and create a huge range of tonal effects. It’s possible to apply Curves directly on an image layer (Image/Adjustments/Curves, or Cmd+M) or alternatively as an Adjustment Layer. In general it is recommended using Adjustment Layers, so that the changes are completely reversible.

The Most Common Curves Adjustements:

(1) The original color image shows part of a Roman fresco. It was already color-corrected by the photographer and is used here only for demonstration purposes.

(2) Lighten an image - click and drag upwards on the line to brighten all the tones in the image

(3) Darken an image - click and drag downwards on the line to darken all the tones in the image.

(4) Add contrast - make an S-shaped curve with two points, one dragged up, the other dragged down.

(5) Target specific tones - adjust one part of the line and pin the rest back along the diagonal with further points.

(6) Set black-and-white points - hold down Alt and drag the bottom sliders inwards until clipped pixels appear.

(7) Fix a color cast - click with the middle eyedropper on a part of the image that should be neutral gray.

(8) Add color shifts - click on RGB, choose Red, green, or blue and adjust the lines by dragging them.

(9) Make interactive tweaks - click on the hand icon, then drag over the image to adjust the tones.

(10) Set colors - double-click the black or white eyedroppers, select a color on the Color Picker, click OK, then click on the image.

Modifications in curves happen by adjusting the shape of the so-called Curve line. The Curve line enables the artist to adjust brightness by altering different parts of the tonal range. The X-axis represents the tone before any change, and it is displayed on a scale from 0 (black) on the left to 255 (white) on the right. The Y-axis represents the changes we make. Dragging the line up past the initial straight diagonal lightens the tones, while dragging it down darkens them. It’s also possible to add multiple points to fine-tune these changes.

To learn more about the context of this tutorial read the following chapter:

Chapter 3, Section 2 - Essential Photoshop Skills for the Artist