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6. Touchup and Enhancement

Photos that are scanned or come from a PhotoCD or digital camera can suffer from both aesthetic and processing defects. These defects can be due to problems of contrast, color casts, color saturation, tonal range, blur, scratches, and so on. Furthermore, most photos, no matter how carefully composed, typically need some enhancement to achieve their full potential. Ansel Adams, one of America's most renown photographers, spent as much time in the darkroom enhancing his negatives and prints as he did in composing and taking his shots. Adams' books on working with the negative and the print are classics in photography [7], [8].

Photo touchup and enhancement is part science and part art, and the GIMP is an excellent tool for these on both counts. This chapter describes the main ideas for aesthetically improving photos and explains how to use the GIMP to achieve terrific results. Following are the topics addressed in this chapter:

- Improving tonal range.
- Removing color casts
- Repairing blemishes
- Sharpening

Each of these subjects is described in detail in the following sections, and a case study is presented at the end of the chapter.

- 6.1 Improving Tonal Range
  - 6.1.1 Highlights and Shadows
  - 6.1.2 Using the `Levels` Tool
- 6.2 Removing Color Casts
  - 6.2.1 The `Curves` Tool
  - 6.2.2 Color Correcting by Balancing the Neutrals
  - 6.2.3 Finding the Shadow, Midtone, and Highlight
  - 6.2.4 Other Colors We Know
  - 6.2.5 The Perturbation Technique
  - 6.2.6 Getting More Detail into the Subject
  - 6.2.7 Other Color Correcting Tools
    - 6.2.7.1 The `Color Balance` Tool
    - 6.2.7.2 The `Brightness-Contrast` Tool
    - 6.2.7.3 The `Hue-Saturation` Tool
- 6.3 Repairing Blemishes with the Clone Tool
- 6.4 Sharpening
  - 6.4.1 The `Unsharp Mask` Concept
  - 6.4.2 A Simplified but Illustrative Example
  - 6.4.3 A Representative Example of Applying
    the `Unsharp Mask`
  - 6.4.4 `Unsharp Mask` Pitfalls
- 6.5 A Case Study

Next: 6.1 Improving Tonal Range Up: Grokking the GIMP Previous: 5.9 Common Problems and
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