Notes on Professional Photoshop 5th Ed.

Terminology

• Chromatic adaptation: the eye perceives ambient lighting as being neutral.
• Simultaneous contrast: the eye exaggerates the difference between the foreground (focus) color and the background; and when shown a large area of similar color, the eye exaggerates the variations vs. what a camera sees (p.46).
• Highlight: the lightest significant area of the image.

Chapter 1

Human color perception is decreased in the darkest parts of a scene. (p.8)

Correcting images with multiple, conflicting light sources usually requires a selection. (p.10)

CMYK is a warmer colorspace than RGB. (p.19)

Added contrast in blue is much less important than in green. (p.20)

When images have significant casts, often the best approach is to use an RGB channel blend. (p.22)

Chapter 2

Key concept: steepen the curve where the subject of interest appears. (pp.28-9)

Set endpoints before starting color correction. (p.32)

Auto Levels moves the endpoints of the image to their darkest and lightest values in the image. (p.35)

The best method for correcting unseen images is to use Auto Levels, followed by a mild S curve on each channel, optionally followed by a slight sharpen. (This is essentially the algorithm that digital cameras apply when creating JPEG images.) (p.36)

When choosing endpoints, ignore specular highlights. (p.37)

To emphasize detail in the highlights/shadow, move the endpoint left/right. To emphasize detail in the midtones, pick a point that's about a quarter of the way down/up the curve and raise/lower it (a quartertone move). (p.37)

Only use an S-curve when you want to add contrast to the midtones. Other curves are needed when highlight and/or shadow detail are important. (p.37)

When an image has important detail in both the highlights and the shadow, beware of using an inverted S-curve to remove detail from the midrange. The eye doesn't adapt both to lightness and darkness simultaneously, so the inverted S-curve doesn't approximate what you'd see in the real scene. See chapters 17-19 for recipes for such images. (pp.40-1)

Blue/yellow add little contrast to the image. You can sometimes get away with steeper curves in these channels than others. (p.44)

In any green object, the two darkest channels are red (cyan) and blue (yellow). The range is darker in the blue than in the red. Natural greens are always biased towards yellow. Therefore, when creating curves of natural scenes, be careful not to force the red to be as dark as the blue. (p.44)

When in doubt, try large corrections on an Adjustment Layer and dial in the opacity to taste. (p.47)

CMYK is a better space than RGB for bringing out critical detail because of the black channel, which tends to produce shorter ranges in the color channels; but watch out for out-of-gamut colors (blues, brilliants, and pastels). (pp.49-50)