Magic Wand
Selections
If you need to select a complicated image
that is sitting on a simple background, if
is often easier to select the background
(using the Magic Wand) and then choose
Select>Inverse to get the subject.
Printer resolution
The number of ink dots per inch (dpi)
produced by all laser printers, including
imagesetters. Most desktop laser printers
have a resolution of 600 dpi, and
imagesetters have a resolution of 1200 dpi
or higher. To determine the appropriate
resolution for your image when printing to
any laser printer, but especially to
imagesetters, see "screen frequency."
Ink jet printers produce a microscopic spray
of ink, not actual dots; however, most ink
jet printers have an approximate resolution
of 300 to 720 dpi. To determine your
printer's optimal resolution, check your
printer documentation.
Screen frequency
The number of printer dots or halftone cells
per inch used to print grayscale images or
color separations. Also known as screen
ruling or line screen, screen frequency is
measured in lines per inch (lpi)--or lines
of cells per inch in a halftone screen.
The relationship between image resolution
and screen frequency determines the quality
of detail in the printed image. To produce a
halftone image of the highest quality, you
generally use an image resolution that is
from 1.5 to at most 2 times the screen
frequency. But with some images and output
devices, a lower resolution can produce good
results. To determine your printer's screen
frequency, check your printer documentation
or consult your service provider.
File size
The digital size of an image, measured in
kilobytes (K), megabytes (MB), or gigabytes
(GB). File size is proportional to the pixel
dimensions of the image. Images with more
pixels may produce more detail at a given
printed size, but they require more disk
space to store and may be slower to edit and
print. For instance, a 1-by-1-inch, 200-ppi
image contains four times as many pixels as
a 1-by-1-inch, 100-ppi image and so has four
times the file size. Image resolution thus
becomes a compromise between image quality
(capturing all the data you need) and file
size.
Another factor that affects file size is
file format--due to varying compression
methods used by GIF, JPEG, and PNG file
formats, file sizes can vary considerably
for the same pixel dimensions. Similarly,
color bit-depth and the number of layers and
channels in an image affect file size.
Photoshop supports a maximum file size of 2
GB and maximum pixel dimensions of 30,000 by
30,000 pixels per image. This restriction
places limits on the print size and
resolution available to an image.
SOURCE:
PHOTOSHOP HELP FILES |
1800 815 166
