Step 1: Calibrate your system
The first and most critical step before making a color or tonal adjustment to a scan is to make sure that you have calibrated your monitor with a monitor profiler, such as ColorVision Spyder Pro. Otherwise, the image’s color on your screen can look vastly different from the same image when printed.
Step 2: Basic goal of the scanning procedure
The basic goal of the scanning procedure is to capture good clean data to work with. Getting a quality scan should almost be a mechanical process, but here you are limited by the quality of your scanner.
This step requires a good scanner and software. Having good original scans gives you the data to work with when you exercise your creative impulses later in an image-editing program like Adobe Photoshop. Don’t get fooled by the high DPI that some cheap scanners boast. The quality of the optics of the scanner is more important, and that’s why you pay more for certain scanners. A good first scan may not look snappy and may not grab your attention, but it will stand-up to your manipulations in the image-processing program so that the final product does look snappy and grabs attention.
Step 3: Check the scan quality and tonal range
It’s important to determine whether your image has sufficient detail to produce high-quality output. In color images, tone corrections are normally carried out before any color corrections are made. An image histogram (found under Photoshop Image controls) graphs the number of pixels at each brightness level in an image. The distribution of pixels in a histogram, especially at its extremities, provides a guide for tonal correction. Stretching out data to fill the histogram increases the contrast. To learn more about histograms and how to use them effectively, you may want to follow the tutorial in the Adobe Photoshop manual.
Step 4: Set the highlight and shadow values
During a low-resolution prescan, some scanners employ automatic density control to calculate specific exposure settings for varying density originals, prior to making the final scan. The lightest tone (Dmin) and darkest tone (Dmax) are automatically located. You can also manually select the white point (Dmin) and black point (Dmax) in Photoshop under the Levels command. It’s important to identify a truly representative highlight and shadow area; otherwise the tonal range may be expanded unnecessarily to include extreme pixel values that don’t give the image detail.
Step 5: Adjust the midtones and fine-tune the tonal correction
Once you have set the highlights and shadows, you may want to fine-tune the contrast. This step is usually not necessary with average-key images because setting the highlights and shadows typically redistributes the midtone pixel values appropriately. For precise control over midtone adjustments, use the Levels midtone slider of Photoshop Curves command.
Step 6: Adjust the color balance
With the tonal correction complete, you can accurately examine and make global and selective color corrections. Unreal colorcasts in the originals can also be removed. Once again, you can use the Levels command or Curves in Photoshop to make selective color corrections. Curves offers the most precise control over pixel distribution with a channel. The commands Hue/Saturation, Replace Color and Selective Color offer additional control over specific color components.
Step 7: Sharpening the image
Unsharp originals are given the impression of being sharper by the application of unsharp masking (USM). This process does not add detail, but heightens the contrast at edges of objects to make them more visible. It is useful for images intended both for print and online.