6. Touchup and Enhancement
Keywords: GIMP, gimp, Gimp, GNU Image Manipulation Program, gnu image manipulation program, Gimp tutorials, GIMP tutorials, gimp tutorials, Linux applications, linux applications, editing digital images, digital image editing, photo touchup, photo enhancement, enhancement photos, touchup, enhancement, image touchup, image enhancement, enhancement images, touchup images, digital collage, collage, compositing, photo montage, montage, photos, images, stock photos, copyright free photos, selection, selections, mask, masks, color correct, color correction, colorspace, colorspaces, RGB, rgb, hsv, HSV, free-hand tool, free hand tool, lasso tool, bezier path tool, Bezier path tool, layer mask, layer masks, layer, layers, gradient tool, gradients, blend tool, blending, threshold tool, thresholding, histogram, curves tool, curves, levels tool, levels, color picker, eyedropper, wilber, wilber the gimp, Wilber the GIMP, magic wand, fuzzy-select tool, fuzzy select tool, crop tool, transform tool, text tool,  [cell cut: 1485 characters, first 1000 kept]

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

#
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
©2000 Gimp-Savvy.com