Absolute Beginner's Guide to Digital Photography

You cannot use adjustment layers on 48-bit images because Adobe wants you to

make your tonal corrections with Curves or Levels and then convert the image to 24-

bit. For this reason, you should use Levels or Curves (or both) to adjust and then

convert the file to 8-bits per channel using Image, Mode, 8 Bits/Channel. Later, you

can edit the file with Photoshop’s tools. Follow these steps to convert from 48-bit to

24-bit:

1. Scan your negative, slide, or photo at 48-bit depth. Use a realistic scan resolu-
   tion: 1200 samples per inch on a 8''×10'' print will not even open in
   Photoshop. Stick to 300 samples on prints, and 1200 samples on medium-for-
   mat negatives, and a maximum of 3200 samples per inch for 35mm nega-
   tives.


2. When the image appears in Photoshop, save it to your computer’s hard disk
   before you make any changes as a TIFF file. Make sure the filename includes
   wording like _48bitor _16bit.


3. Make your adjustments in Image, Adjust, Levels or Image, Adjust, Curves.


4. When you’re satisfied with the look of the image, convert to 24-bit using
   Image, Mode, 8 Bits/Channel.


5. Save the new 24-bit image on the hard drive with a new name and then
   delete the massive 48-bit file, or burn it onto a CD/DVD-RW as a backup.

You really do not need to work with every image at 48-bit depth; only with the most

important images in your collection. For casual photography, 24-bit depth is fine.

After sitting through (actually, sleeping through) a 48-bit scan, you will see why this

feature is only worthwhile on your most important images.

Output Resolution

Images that output (print) on a printer use dpi for their resolution. This includes

laser printers, inkjet printers, dye-sublimation printers, and even offset printers. The

latter are used to print magazines, newspapers, and books.

You can read more about printer resolution and dots in Chapter 18, “Printers and

Printer Resolution.” The next section will explain how you can upsize an image that

might not be at a resolution you can use. This process of interpolation is not fool-

proof, and is often a last-resort method for salvaging an image.

Digital Methods for Increasing Resolution

Photoshop and other image editors are capable of increasing the resolution of an

image using interpolation. Interpolationis a software technique that uses mathemati-

cal algorithms to increase the number of pixels in an image (see Figure 12.6). This

186 ABSOLUTE BEGINNER’S GUIDE TODIGITAL PHOTOGRAPHY