The Short Answer
To Resolution
All digital images are made up of tiny squares called pixels,
and each pixel has a specific location, size and a very specific
color value. Digital cameras capture images at 72 “pixels per
inch” (ppi) multiplied by the number of pixels present on the
image sensor. Scanned images and image editing software allow
you to choose your resolution. The pixel size is determined by
the resolution of your image and is actually inversely
proportional to resolution. In a 24-bit (RGB) color image, there
are 256 possible shades of red, green, and blue mixed to
represent the color of each individual pixel. 256 shades of red,
green, and blue can be combined to produce a total of 16.7
million different colors. 16.7 million colors are sufficient for
photo-realistic output.
 Printer
resolution is given as the number of “dots per inch” (dpi). Dpi
is the maximum number of ink dots that the printer is capable of
placing on your paper per inch. Photo-quality ink-jet printers
spray ink through multiple nozzles to produce various sized
droplets with variable droplet spacing. When the droplets are
sprayed onto paper the drops overlap, combine, or are spaced so
as to reproduce the color of the individual pixel being printed.
The printer may have to spray a drop of all six colors on top of
each other to generate a dark color. In other words, it takes
multiple drops of ink from the printer to create the color in
each square pixel. So even if the printer resolution is given as
1440 dpi it does not mean that there are 1440 dots lined up in a
row in each inch of the print. Much to the surprise of most
people, the printer’s resolution numbers have nothing to do with
the size of, or the number of pixels in your image. Pixels per
inch (ppi) and dots per inch (dpi) refer to totally different
things.
It would not be advisable to send your printer a file with the
camera or input resolution being the same as the stated printer
resolution. In fact, you only need to send a file closer to 240
- 300 pixels per inch. This solution is ideal, as this allows
the printer maximum flexibility in combining the ink colors to
generate the color of each pixel. If you were to send an image
sized at 1440 ppi to your printer it would simply throw out most
of your data. The worst part is that in the printer driver
interpolation, you have no idea which pixels the printer (and
its software) will decide to get rid of, and your printed
results would be totally unpredictable.
Images that will be viewed on a computer monitor such as those
destined for e-mail or display on the worldwide web should be
sized to a resolution of 72 ppi. This is because image pixels
will be translated directly into monitor pixels. The size at
which the image will actually be displayed is dependent on the
size of the viewer’s monitor, the monitor’s resolution setting,
and the actual pixel resolution of the monitor. When the image
resolution is higher than the monitor resolution, the image will
be displayed on screen at a larger size than the print size.
Therefore viewer would have to scroll all around to view the
image, which would be inconvenient. For example, if you want to
e-mail an image and be certain that it does not exceed the size
of the recipient’s monitor you would size it for 4x6 inches and
set the resolution to 72 ppi. If the recipient’s monitor is a
72-ppi monitor (Mac) the image will display at 4 x 6 inches, and
if they have a 96-ppi monitor (PC) the image will display at 3 x
4.5 inches. Both image sizes would easily fit on a small monitor
without having to scroll to see the whole image.
Image resolution may be set, changed, or viewed in any editing
software program, such as Adobe’s Photoshop. Photoshop is
expensive and it requires a long learning curve to operate, but
it is the worlds most often used editor. Editing software is
where all color, cropping and repairs decisions are made. It is
also where resolution is determined for web use, e-mailing, or
printing.
Remember to keep your “ppi” separate from your “dpi” and imaging
will be much smoother. |
