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the curve (Figure 5.27). However, if you click to add a curve point and at the same time drag the mouse up or down in the image window, this will simultaneously move the curve up and down at where you just added the curve point. This means that when the target adjustment tool mode is active, you can click and drag directly on the image to make specific tone areas lighter or darker (see the step-by-step example opposite). Note that if you can get the cursor to hover over an existing curve point you can -click to delete it from the curve line. With both the eyedropper and the target adjustment tool methods, the pixel sampling behavior is determined by the sample options set for the eyedropper tool (see Figure 5.28). If a small sample size is used, the curve point placement can be quite tricky, because the hollow circle will dance up and down the curve as you move the cursor over the image. However, if you select a large sample size this will average out the readings and make the cursor placement and on-image editing a much smoother experience. Note that in Photoshop CS5 there is now an ‘Auto-Select Targeted Adjustment Tool’ Adjustments panel mode option that automatically selects the target adjustment tool whenever a Curves adjustment layer is made active.

Figure 5.27 When the cursor is dragged over the image, a hollow circle indicates where the tone value is on the curve.

Figure 5.28 The eyedropper tool Options bar showing the Sample Size options. For on-image selections it can be useful to choose a large sample size. Note also the ‘Show Sampling Ring’ option that can be used to enable/disable the sample ring display.

Adding curve point tip

In non-target adjustment tool mode, if you select the eyedropper tool from the tools panel, you can -click to add a point to the curve.

1.

I deliberately chose a photograph that lacked contrast in order to demonstrate how the on-image curves editing works. To begin with I added a new Curves adjustment layer and made sure that I had a large sample size set for the eyedropper tool options.

2.

I then clicked on the target adjustment tool button (circled) and moved the cursor over the image. I was then able to click with the mouse on the image to add new points to the curve. As I dragged the cursor upwards, this raised the curve upward and lightened the tones beneath where I had clicked in the image. Likewise, as I dragged downwards I was able to darken these tones in the image.

Direct Curves dialog

Many of the options in the direct Curves dialog are the same as those that can be found in the Adjustments panel. However, in addition to these there is a ‘Show Clipping’ option for turning on the shadow and highlight clipping threshold preview when dragging the black point or white point input sliders. In the Adjustment panel the Curves mode is selected automatically, selecting the Light Curves mode for RGB images (which shows the levels range from 0–255) and the Pigment/Ink Curves mode for CMYK images where the curves values are expressed as percentages (the Pigment/Ink Curves mode is preferable for repro users who prefer to see the output values expressed as ink percentages when editing CMYK images). In the direct Curves dialog you aren't as restricted as you are in the Adjustments panel because the Curve Display Options section at the bottom allows you to manually choose between the Light Curves mode or the Pigment/Ink Curves mode regardless of the color mode the image is in. There are also button options to switch between showing 25% or 10% increments in the graph display, although you can toggle the display by -clicking in the graph area, just as you can in the Adjustments panel.

When to use direct curves

The same principles apply here as with the Levels adjustments. Adjustment Curves are the ideal solution for most image editing tasks, but if you wish to edit individual Photoshop channels or layer masks, the only way to do this is by using direct Curves adjustments.

The remaining options are normally on all the time in the Curves Adjustments