Printing - Black and White in Photoshop CS4 and Photoshop Lightroom - page 261

camera, these numbers will be the maximum size your camera is capable of
capturing at its native resolution. The top portion of the Image Size dialog
box will illustrate what those pixel dimensions are. Be warned, however,
these numbers can be easily and haphazardly changed having potentially
detrimental ef ects on your image.
Resolution
For printing purposes, the term “resolution” in the Image Size dialog box
refers to the number of pixels per inch that would be required to produce a
i nal output print. Resolution can be presented with the formula: image size
physical dimension (ppi or pixel per inch) resolution. This means that there
is a reciprocal relationship between pixel size, the physical dimensions of the
image and resolution.
Digital images are made up of pixels which are resolution-dependent. An
image can be scaled up, but as the size of the image is increased, the i nite
information and number of pixels available can only be stretched and diluted
so much before the image begins to deteriorate, and the underlying pixel
structure becomes increasingly visible.
File Size
The i le size of an image is measured in bytes, kilobytes, megabytes or
gigabytes. This refers to the sum total of pixel information or simply the total
number of pixels.
The Image Size dialog box
There are two important checkboxes within the dialog box: Constrain
Proportions and Resample Image. Unless you i nd a creative aesthetic for
distorted images, “Constrain Proportions” should always remain checked.
The Resample Image checkbox is where you take control of pixel allocation,
resampling, interpolation and subtraction.
It is the best practice to always start with the Resample Image box unchecked,
as this will protect your image from any potential haphazard up or down
sampling. This will constrain the width, height and resolution of the image
and merely redistributes the pixel allocation. The actual pixel count and total
i le size within the image will remain unchanged no matter what numbers
you type in each i eld. Type in the desired resolution for the image's output
destination. Screen resolution is 72 ppi, which is best for web work, while
inkjet printers need between 180 and 360 ppi for quality rendering, and of set
printing (books, magazines, etc.) requires 300 ppi. Be sure to ask your service
bureau for their recommendation.
Once you have set the resolution, check to see if the width and height
dimensions of the image now presented meet your specii cations.