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save and load presets, so you can easily add your own custom settings to this list. The middle section contains the main adjustment controls and at the bottom you again have the clipping control to switch between applying the adjustment to all the layers that are below or only to the layer that's immediately below. Next to this there is an eyeball icon for turning the adjustment layer visibility on or off. Further along there is a button for switching between the previous state and the current edited state, where if you click and hold the mouse down (or hold down the key) you can see what the image looked like before the last series of image adjustments were applied. Lastly, there is a Reset button for cancelling the most recent adjustments and a Delete button to remove the current adjustment layer.

Figure 5.18 The Adjustments panel adjustment mode options.

Levels adjustments

There was a time when every Photoshop edit session would begin with a Levels adjustment to optimize the image. These days, if you use Camera Raw to process your raw or JPEG photos, there shouldn't be so much need to use Levels for this purpose – you should already have optimized the shadows and highlights during the Camera Raw editing. However, it is important and useful to understand the basic principles of how to apply Levels adjustments since there are still times when it is more convenient to apply a quick Levels adjustment to an image, rather than use Camera Raw. Direct Levels adjustments are always useful for editing channels and layer masks and you can also use Levels adjustment layers to create dodging or burning layers. The main Levels controls are shown below in Figure 5.22.

Figure 5.22 This shows a view of the Adjustments panel for adding Levels adjustments. The Input sliders are just below the histogram display and you can use these to adjust the input shadows, highlights and gamma (the relative image brightness between the shadows and highlights). Below this are the Output sliders and you use these to set the output shadows and highlights. It is best not to adjust the output sliders unless you are retouching a prepress file in grayscale or CMYK, or you deliberately wish to reduce the output contrast.

Auto image adjustments

The Auto button sets the clipping points automatically (the Auto settings are all covered later in this chapter).

Analyzing the histogram

Levels adjustments can have a big effect on the appearance of the histogram and so it is important to keep a close eye on the histogram shown in the Levels dialog/Adjustment panel as well as the one in the Histogram panel itself. Figure 5.20 shows a nice, smooth histogram where the image was recently optimized in Camera Raw before being opened in Photoshop, while Figure 5.21 shows the histogram for an image that's obviously been heavily manipulated in Photoshop. In Figure 5.23 you can see how the blacks are quite heavily clipped and most of the levels are bunched up to the left, while in Figure 5.24 the highlights are clearly clipped. Although, as I explain below, it isn't necessarily a bad thing to sometimes clip the shadows or highlights in this way.

Figure 5.20 This histogram shows an image that contains a full range of tones, without any shadow or highlight clipping and no gaps between the levels.

Figure 5.21 A histogram with a comb-like appearance indicates that either the image has already been heavily manipulated or an insufficient number of levels were captured in the original scan.

Figure 5.23 If the levels are bunched up towards the left, this is a sign of shadow clipping. But in this example we would probably want the shadows to be clipped in order to produce a rich black background.

Figure 5.24 If the levels are bunched up towards the right, the highlights may be clipped. But in this image I actually wanted the white background to burn out to white.

Using Levels to improve the contrast

1.

I chose here to use a monochrome photograph, since it would make the following contrast enhancing Levels adjustment clearer to