Digital Photography for Graphic Communications
Chapter 5 • Image Fidelity
Publishers who want “critical” or “match colour” want the closest possible match to the original. Think of a high-quality magazine cover with a still life with flowers, food, and household products. The same criteria could apply to an individual product in an online or print catalog, a portrait, a fine-art reproduction—anywhere accurate colour is required.
Colour accuracy has an obvious impact on consumer satisfaction. If colour the colour is not striking enough then consumers may not be attracted to the product. And if the product looks better in the photo than in real life, consumers may be dissatisfied and return it or leave poor reviews.
For achieving critical colour, the authors suggest the following steps.
Exposure
If the old axiom, “garbage in, garbage out” is true, then a good photo starts with proper camera setup.
- Set up the digital camera with the proper exposure and white balance, as described in Chapter 3.
- For copy work, place a grayscale target next to the original for later use in setting highlight, shadow, midtone, and gray balance (described in Editing below).
- Bracket exposures ±1/3 or 1/2 exposure value (EV) to provide a range from bright to dim.
- Check the histogram on the digital camera’s screen or in the image-editing software to make sure no tones have been cut off (Figure 5-1).
- Look at the bracketed exposures on the big screen and choose the one with the best looking tone and colour.
Editing
The advent of colour scanners in the early 1980s enabled printers to make colour separations in a few minutes rather than the few hours required to make them in an enlarger. At that time system vendors and research associations developed a procedure for making the best separation on the first scan: set the contrast of the scan to the range available with the ink and paper.
Scanner operators were taught that lithographic presses could reproduce a “smallest printable dot” of 3% dot area before dots would “blow out” or fail to image, and a “largest printable dot” of 97% before shadow dots would “fill in” or blend together—in both cases losing image detail.
Scanner operators also attached a grayscale, a small target with a stepped or continuous series of tones, for use in setting the highlight, shadow, and midtone on originals (Figure 5-2).
You can apply the same strategy today by setting the highlight dot to 3% on the CMYK scale or 247 levels (3% of 255, where level 255 is white) and shadow to 97% (8 levels, where level 0 is black).
Separators also set the midtone, or midpoint, of the reproduction according to the original’s “key,” or predominant brightness level. They realized that high-key, or mostly bright, photos need more highlight contrast and adjusted the midtone to increase contrast in the highlights, at the expense of shadows (Figure 5-3). Likewise, predominantly dark, or low-key, photos needed more shadow contrast.
- Set lightest density of photo to