Adobe PHOTOSHOP 6.0 Manual page 106

CHAPTER 2
96
Getting Images into Photoshop and ImageReady
About resampling
Resampling refers to changing the pixel dimen-
sions (and therefore display size) of an image.
When you downsample (or decrease the number of
pixels), information is deleted from the image.
When you resample up (or increase the number of
pixels), new pixels are added based on color values
of existing pixels. You specify an interpolation
method to determine how pixels are added or
deleted. (See "Choosing an interpolation method"
on page 96.)
A
A. Downsampled B. Original C. Resampled up
(Selected pixels displayed for each image.)
Keep in mind that resampling can result in poorer
image quality. For example, when you resample an
image to larger pixel dimensions, the image will
lose some detail and sharpness. Applying the
Unsharp Mask filter to a resampled image can help
refocus the image's details.
For more information, see "Sharpening
images" in online Help.
You can avoid the need for resampling by scanning
or creating the image at a high enough resolution.
If you want to preview the effects of changing pixel
dimensions on-screen or print proofs at different
resolutions, resample a duplicate of your file.
B C
Choosing an interpolation method
When an image is resampled, an interpolation
method is used to assign color values to any new
pixels it creates, based on the color values of
existing pixels in the image. The more sophisti-
cated the method, the more quality and detail
from the original image are preserved.
The General Preferences dialog box lets you
specify a default interpolation method to use
whenever images are resampled with the Image
Size or transformation commands. The Image Size
command also lets you specify an interpolation
method other than the default.
To specify the default interpolation method:
1 Choose Edit > Preferences > General.
2 For Interpolation, choose one of the following
options:
• Nearest Neighbor (Jagged) for the fast but less
precise method. This method is recommended for
use with illustrations containing non-anti-aliased
edges, to preserve hard edges and produce a
smaller file. However, this method can result in
jagged effects, which become apparent when
distorting or scaling an image or performing
multiple manipulations on a selection.
(Photoshop) Bilinear for a medium-quality
•
method.
Bicubic (Smooth) for the slow but more
•
precise method, resulting in the smoothest tonal
gradations.