Datasheet

images. Bicubic Sharper is like Bicubic but with enhanced sharpening; Bicubic Smoother
is like Bicubic but with less sharpening. Bicubic resampling can be used for both upsam-
pling and downsampling images.
While making up information and decimating it sound like bad things, each has its
purpose. Usually you should avoid upsampling—especially if such options as rescanning
or returning to an original camera image exist for gaining more detail. However, images
can be upsampled with some success, depending on the desired quality—provided the
change isn’t huge. Upsampling 10 percent or even 20 percent may not be noticeable if the
source image is sharp. Usually you will upsample only to make up small gaps between the
resolution you have in an image and what you really need or to adjust borrowed image
components (elements you are compositing from other images).
Downsampling, while certainly damaging and compromising to image content, should
be less noticeable in your results if you use the right sampling methods. Image informa-
tion indeed gets averaged or eliminated, but if downsampling is being done for the right
reason, any details you lose in resampling would have been lost on output or display any-
way. Detail loss is inherent in the process of downsampling, or outputting images at a
smaller size. Even if equipment can reproduce detail at a smaller size, eventually details
will pass the limit of the human eye’s ability to discern them. In other words, at some
point you lose the details anyway.
Find even more information on image resizing and interpolation in the Resolution
section of the Appendix, under “Interpolation.”
Multipurpose Images
Making images that you’ll use for more than one purpose (for example, print and Web)
can cause a little problem considering the resolution and resizing issues already discussed.
Optimally, you’d like to work with images so that you target the result. Doing so ensures
that you retain all of the actual image detail rather than relying on interpolation or decima-
tion and your choice of sampling type to interpret detail. However, you can’t work on an
image at two resolutions or in more than one color mode at the same time. It is a simple
fact that an image going to print on a high-resolution printer should have more informa-
tion than one at the same size used on the Web. This is because of the difference in the way
these media use image information. In fact, different printers and printer types will have
different optimal utilization of image detail because of their mechanics. You will need to
target image information to your output or you will not optimize detail.
You have only two solutions in working with dual-purpose images:
• Create more than one image, each with a specific purpose.
• Create one image and resize it.
10 ■ chapter 1: Resolution: The Cornerstone of Image Detail
4456c01.qxd 3/1/06 3:04 PM Page 10