Resolution
What is
resolution?
Resolution it is
the number of pixels per inch for scanners, or dots per inch on your screen,
and lines per inch for your printer.
Why is
resolution important to me?
Resolution will affect
the quality of your print (final output) of your image. An image that is scaled
up does not increase in quality. If an image has a resolution or 72 dpi for
example and you scale that image by 200%, then you will most certainly experience
some image degradation.
It is important
to know the correct resolution to scan you image at, work in and print with.
Photoshop allows
you to change the image size and resolution very simply be going to image size
and typing in the desired numbers. But be aware of what will happen when you do
this. When opening an image in Photoshop it places all the pixels defined in
your file on the grid. When you change these pixels by changing the size or
resolution of the file it must change all the pixels in the image, which is
called resampling. When you increase the resolution Photoshop has to make up
all the pixels that need to be added. Since Photoshop only understands color
and pixels it is basically using math to analyze each pixel and make up new
ones.
Since Photoshop
is basically guessing at what should be added for the best quality you should
limit and if possible prevent having Photoshop resample your image. Below is an
example of what happens when reducing to 25% and then enlarging 400% back to its
original size just one time.
Original
Image
Resized Image
to 25%
Resized Image
back to 400%
Since this
obviously reduces the quality you want to reduce resampling. In order to do
this you need to know the final use of the image before you start scanning or
working on it. For on screen presentations like power point presentations and
web pages you only need to have a 72 dpi image. If you plan on printing your image you need to have
a 200-300 dpi image
in most cases.
Now that you
know the output resolution needed you need to know if you plan on resizing the
image after you scan it. So if you are scanning a 4x5 inch photograph that
needs to be printed at 200 dpi at 8x10 then you need to scan it in at 400 dpi.
The easiest way
I have found to calculate this is to open a new file in Photoshop and type in
the width, height and resolution the image needs to be when printed. This will
give you a file size, in the above example it is 9.16 megs for an RGB image.
When you scan an image no matter what size the original is you need to have
approximately a 9 meg file. Most scanning software will give a file size when
setting the resolution. So when scanning crop you image in the scanning
software and adjust the resolution to give the desired file size.
Using the
correct resolution is very important for both efficiency and quality. If the
image is at two high of a resolution it will take longer to open, correct, save
and print the file. If you use too low of a resolution the quality will suffer.