Working with 16-Bit per Channel Scans and Files
A very useful technique, especially when working on the highest-quality art prints, is to do 16-bit scans, or digital capture, then work in 16-bit per color channel mode instead of 8-bit color. This gives you up to 16 bits per RGB, Lab, or CMYK channel of information instead of the usual 8 bits. Photoshop 6 and 7 support Marquee and Lasso selection, Cropping, Levels, Curves, Hue/Saturation, Color Balance, Brightness/Contrast, Channel Mixer, the Eyedropper, the Add Noise, Dust and Scratches, Median, Solarize, High Pass, Gaussian Blur and Unsharp Mask filters, the Rubber Stamp and several other tools in 16-bit per channel color mode. Layers of all kinds are not supported at more than 8 bits per channel so you will not want to do all your work in 16-bit per channel mode. To convert an image to 16-bit color, just choose Image/Mode 16 Bits/Channel.
Figure 14.15 Here are the controls for the Nikon 8000 scanner set up to do 16-bit per channel scans. This scanner actually scans 14 bits of information per channel but in Photoshop 6 or 7 the two choices are either 8 bits per channel or 16 bits per channel, so when you actually do 12 or 14 bits in your scanner and save this as a TIFF file, it will show up as 16 bits within the Photoshop 6 and 7 user interface.
If you get a scan from a really good scanner, the scanner will be actually scanning the file getting more than 8 bits per channel of RGB information. When you adjust the curves and other controls in the scanner software, what you are really doing is deciding how to convert from the more than 8 bits of information that the scanner gets down to the 8 bits of information per channel that is in a standard RGB file. When you do that conversion, you are throwing away information that you got from the scanner, and sometimes you end up throwing away the wrong information or you want some of it back later. At this point, you may need to rescan your original to get that information. Many scanners these days, including the Nikon 4000 & 8000 and the Polaroid Sprintscan 120, allow you to save all 16 bits per channel of information exactly as it comes from the sensors on the scanner, a raw scan. This way, assuming you have a great scan from a great scanner, you might never need to scan the original again because you can always reprocess that 16-bit per channel raw scan data down to 8 bits in a different way to pull out a different area of detail.
You can actually do your overall color correction on 16-bit per channel files using Photoshop 6 and 7 to improve the histogram, colors and contrast of that original raw scan without throwing away any information. This allows you to do one raw scan and then save that and actually be able to make most of your scanner decisions later or over again without actually rescanning. In Chapters 19 and 26 of our step-by-step examples, Photoshop 7 Artistry will show you how to change your workflow to do your overall color correction using 16 bits per channel and get much more from your scans. Check out Chapter 16: "Image Resolution, Scanning Film and Digital Cameras," to get a lot of good ideas of things to consider when making 8-bit or 16-bit per channel scans.