This extract is from chapter 4 of the Wiley title 'Lightroom 4: Streamlining Your Digital Photography Process
' by Nat Coalson.
After adjusting the settings on the Basic panel, you can further refine the photo's contrast by manipulating specific tone ranges with the Tone Curve panel (see Figure 4–26). If you’ve used curves in Photoshop or other software, the Tone Curve panel may seem familiar to you. The horizontal axis represents the original, unaltered values in the image, with the black point at the left and the white point at the right. The vertical axis represents the adjustments you make. The background of the curve box shows a histogram and a highlighted area indicating the minimum and maximum range of curve adjustment possible, based on the split controls in effect (see below).
Most photos probably won’t need the Tone Curve
You should usually focus the majority of your tone adjustment work on the Basic panel instead of the Tone Curve, which is becoming outdated in the era of parametric processing. The processing algorithms used for Basic panel sliders are provide more sophisticated processing routines than a curve. Especially with PV2012, you may find you can make your photos look just how you want without ever touching the Tone Curve panel. Don’t be fooled into thinking that just because it’s there that you need to use it for every photo! However, when you need very precise control, nothing works like the Tone curve; other practical uses are advanced colour correction and creative effects using Lightroom 4’s new per-channel curve capabilities.
Lightroom’s default Tone Curve is parametric: it adjusts sections of the tone scale, rather than from individual points. This provides smooth transitions between tone ranges and reduces the possibility of introducing undesirable hue shift s and posterization (banding).
Adjust the curve to increase or decrease contrast in specifi c areas of the tonal range. Positive values lighten tones and negative values darken them. The steeper the curve (or section of the curve), the higher the contrast. The flatter the curve, the lower the contrast. A typical example of this is the application of an “S” shaped curve, which increases contrast in the photo by lightening highlights and darkening shadows. Thus, the midtone section of the curve displays a steeper slope than before the adjustment (see Figure 4–27).
You can adjust the Tone Curve in the following ways:
The Targeted Adjustment Tool (tat): click the bull’s-eye to activate the tat, and then either click and drag up or down in the image, or use the up and down arrow keys. See the next section for more information about the Targeted Adjustment Tool.
In the parametric curve, drag the sliders to adjust the four tone ranges independently: Highlights, Lights, Darks, and Shadows. The curve will be adjusted accordingly. Using these sliders is the easiest way to adjust the curve.
Click and drag on the curve: up to lighten, down to darken. In the point curve, click to place points on the curve. Drag the points to change the tone values. In the Point Curve mode, the numeric values of point adjustments are shown at top left of the Tone Curve.
Select a preset from the Point Curve menu: Linear, Medium Contrast or Strong Contrast.
The split point controls on the bottom axis of the curve box define the range of adjustment for each of the four regions (see Figure 4–28). As you drag the split controls, the slider background adjusts to display the range of tones available for each region. Using the split controls you can achieve very precise control over the curve adjustment.
Click on the Point Curve button in the bottom right corner (see Figure 4–28) to switch from the parametric curve to the point curve (see Figure 4–29). Th e two curves are separate, and their eff ect on the photo is combined. Lightroom’s point curve editor provides more precise control than the parametric curve, and is similar to point curves in Photoshop and Adobe Camera Raw, with a couple of differences:
No Input and Output text boxes (no numeric entry of point values).
Percentages instead of 0-255 values.
Does not retain focus on a point after it’s been edited (point does not stay selected).
You can delete a control point with right-click or double click, or by dragging it out of the curve box.
Flatten the curve (remove all control points adjustments) using the menu option with right-click or Ctrl-click.
Holding option/alt requires more mouse movement and provides finer control.
Point Curve Presets
You can save point curve settings (as xmp files) in the Curves folder (which is shared with ACR curves). When saving Develop presets including the Tone Curve settings, the point curve gets saved along with parametric values in the Tone Curve part of the preset—not independently.
New in Lightroom 4: With PV2012, the default Point Curve is Linear, although the default processing applied with Linear is similar to PV2010’s Medium Contrast. This is one reason why photos using PV2012 look different even with default settings.
Using Lightroom’s Point Curve, you can invert a negative image to a positive, and vice versa.
Warning: Previous point curves get reset in Lightroom 4.0
A serious bug has been reported in Lightroom 4.0 affecting custom point curves applied in earlier catalog versions that have been upgraded. In many cases, custom point curve data has been lost and reset to the default. If you use custom point curves and upgraded your previous catalog to Lightroom 4.0, you should carefully check for these changes. You may need to revert to your old catalog (hopefully, you’ve backed it up). By the time you read this, a fix will likely be available in a minor point upgrade. If you think this might affect you, be sure to look into the current status of the fix and upgrade to the latest version of Lightroom as recommended.