Graphics Programs Reference
In-Depth Information
Scanned images often suffer because they do not use the full dynamic range
available in the image file. Figure 1.18 shows a histogram (which you'll learn more
about in Chapter 3) representing the full dynamic range. The white portion of
the graph (on the left side) means the pixels are not distributed properly to take
advantage of the darkest tones available in the image file. You'll learn how to
adjust the histogram with the Levels command in Chapter 11, “Adjusting and
Filtering.”
FIGURe 1.18
The histogram
shows that this scanned image does not
take advantage of the full dynamic range.
Professional printing presses create rows and columns of cyan, magenta, yel-
low, and black colored dots. In much the same way as with mosaics and pixels,
we perceive continuous tone when printed dots appear small enough in printed
matter. A problem called
moiré
(see Figure 1.19) sometimes arises with scans
because of the interference between the grid of printed dots and the grid of pix-
els in the scan.
FIGURe 1.19
Moiré interference pattern
