Step 2: Check The Scan Quality And Tonal Range - Adobe PHOTOSHOP 5.0 User Manual

112 CHAPTER 6
Making Color and Tonal Adjustments
Step 2: Check the scan quality
and tonal range
It's important to determine whether your image
has sufficient detail to produce high-quality
output. The higher the number of pixels in an area,
the greater the detail. Bad photographs or bad
scans can be difficult if not impossible to correct.
Too many color corrections can also result in loss
of pixel values and too little detail.
If you save a copy or use adjustment
layers, you can always revert to the
original image.
A histogram graphs the number of pixels at each
brightness level in an image. It can show you
whether an image contains enough detail to make
a good correction. It also gives a quick picture of
the tonal range of the image, or the image key type.
A low-key image has detail concentrated in the
shadows, a high-key one has detail concentrated in
the highlights. An image with full tonal range has
a high number of pixels in all these areas. Identi-
fying tonal range helps determine appropriate
tonal corrections.
A quick way to adjust an image that's too
dark is to move the white point to where
the pixels begin, using the histogram in the
Levels dialog box.
LOOKING AT THE HISTOGRAM The histogram
shows how the pixels' values are distributed in an
image, and whether the image contains enough detail
in the shadows (shown in the left part of the
histogram), the midtones (shown in the middle), and
the highlights (shown in the right) to produce a good
correction.
Original with insufficient detail, and sufficient detail
Original, and corrected average-key image
Original, and corrected high-key image
Original, and corrected low-key image