Adobe Photoshop CS5 for Photographers - Martin Evening [94]
The Brightness slider is different. It is a midtone correction tool that behaves much like the Gamma (middle input levels) slider in the Photoshop Levels dialog and can also be used to make a photo appear relatively lighter or darker. The difference here is that the Brightness slider adjusts the image tones by compressing one end of the tonal scale as it expands the other. In this respect, the Brightness control should be regarded as a more brutal image adjustment than the Exposure slider, which is why you are always advised to use Exposure first to get the brightness right, use Recovery to compensate for any undesirable clipping and then use the Brightness slider to fine-tune the photo's brightness.
Figure 3.37 illustrates how these adjustments affect the Histogram. In the top histogram view, the Exposure adjustment sets the highlight clipping point and evenly expands or compresses all the tones that are darker than this. The middle histogram shows how if you make a positive, lightening Brightness adjustment, the brighter tone levels are compressed, while the darker tones tone levels are expanded. Conversely, if you apply a negative, darkening Brightness adjustment, the highlight levels are expanded and the shadow tones become more compressed.
Figure 3.37 The top histogram shows how the Exposure slider adjusts the highlight clipping so that the midtones and shadows adjust smoothly relative to this point. The Brightness slider adjusts the brightness by shifting the levels between the set shadow and highlight points. The middle histogram shows the effect of a positive Brightness adjustment and the bottom histogram shows the effect of a negative Brightness adjustment.
Figure 3.38 clearly illustrates the practical consequences of applying an Exposure-led adjustment versus Brightness. In the top image you will notice that where I only used the Brightness slider to lighten the image there is less contrast in the flower petals and therefore less detail. This is because the highlight levels have become compressed and this has resulted in flatter contrast in the midtone/highlight areas. None of this is to suggest that you shouldn't use Brightness. Far from it. Although compressing and expanding the levels is a destructive process, this is just an inevitable part of the digital image editing process. The main point to learn from all this is to use the Exposure slider first to ‘expose’ the image to obtain the best brightness and use the Brightness slider as a secondary adjustment to ‘fine-tune’ the brightness.
Figure 3.38 Superficially these two close-up views look the same. In the top version I used the Brightness slider only to adjust the image brightness. In the lower one I used the Exposure slider first to set the highlight point clipping and brightness and then used the Brightness slider to fine-tune the brightness. You should be able to see more highlight contrast and detail in this version.
Negative Exposure
A negative Exposure adjustment can be used to help recover highlight detail that would otherwise have been clipped. If an image initially appears overexposed, it is best to use the Exposure slider first to find the best exposure, use the Recovery slider to fine-tune detail recovery in the highlights and use the Brightness slider last to fine-tune the image brightness.
Contrast
The Contrast slider applies a non-linear contrast type adjustment. In Photoshop terms it is equivalent to applying an ‘s’ shape curve to the image. But unlike the Contrast slider in the legacy version of Photoshop's Brightness/Contrast image adjustment, the Camera Raw Contrast slider never forces the levels to clip at either end of the tonal scale and is completely safe to use. A positive contrast adjustment creates a steeper ‘s’ shape type curve which therefore increases the image contrast, while