Resolution:
The Peanut Butter Analogy
When you scan an image or take a
digital picture you are “collecting”
a batch of pixels. The mega pixel
rating of your camera or your
scanner’s sensitivity will determine
how many pixels of information
you can collect.
In digital terms, the image doesn’t
really have a fixed dimension but it
has a volume that’s defined in
pixels per inch.
Let’s say we start with a 5 Mega
Pixel image. (That’s 5 million pixels)
The same volume of pixels can be
spread thickly so that the image
has more resolution but is smaller
in length and width.
For example: 4 x 5 inches at 300
pixels per inch
or
We can spread those pixels more
thinly so that the image has less
resolution but is larger in length
and width.
For example: 8 x 10 inches at 150
pixels per inch
What’s the Point?
OK…enough of the peanut butter!
The point is that you collect
information about a picture when
you digitize it through scanning or
digital photography.
Here’s what’s really important; at
the point of digitizing an image you
are collecting the best information
possible. No matter what you do
with it in Photoshop you’ll never
have more accurate information
(pixels) than at the moment of
digitization.
Sources for digitized images
Digital Cameras capture 1.0 to 10 Mega
Pixels. You’re the photographer
Scanners have a wide range of resolution
depending on quality 72-1200 ppi is
typical.
Drum scanners capture up to 64,000 ppi
Images copied off the web are at a very
low resolution of 72 ppi
You can purchase digitized images from
Photo sites like Corbis.com
Resolution typically tops out at 300 ppi
What Resolution Do I need?
Here’s the basic rule of thumb:
How you plan on using the image dictates
how much resolution you need!
Web uses 72 ppi
Laser color printing 150-200 ppi
High end 4 color printing 300 ppi
!
Excessive resolution crates large files and
does not improve print quality!
PPI vs DPI
Pixels per inch refers to scanner,
camera, and monitor resolution.
Dots per inch refers to the physical
output detail of a printer.
If you know your printer output resolution you can
calculate what image resolution would result in the
best print.
Here’s the formula:
Output dpi divided by 3=optimum input ppi For example: 600 dpi/3=200 ppi
Dealing with Resolution in
Photoshop
You’ve opened an image in Photoshop…your first
stop in should always be Image>Image Size!
What’s your image resolution and dimensions?
File size
Without resample
selected your image
will be like the peanut
butter example. A
change in resolution
will result in a
proportional change to
width and height. The
overall file size won’t
change.
With resample
selected your image
will resample. Pixels
will be added if you
choose a resolution or
dimension that’s
larger than the
original image.
Caution: more pixels
doesn’t mean a bad
picture will look
better!
Again, what’s the
Point?
The concept of resolution,
resampling, ppi and dpi are
essential to understanding and
working with Photoshop at a
professional level.
The best way to learn this is to do
it. Open a variety of images in
Photoshop and then go directly to
the Image>Image Size box and
see what happens.
!
What’s With All The File Types?
Photoshop Files
PSD-native file format/supports all features in PS
- Save your master or archive files
- Lossless compression
!
JPEG/JPG-Most widely used for viewing and sharing
digital files
- Lossy Compression (compression artifacts)
- Reduced file size
- Used by all image editing layout programs
GIF-Optimized for web graphics
- Supports transparency
Photoshop Files
PNG-Primarily for web graphics 8 and 24 bit
- Lossless compression
- Alpha transparency
- Does not support CMYK Printing
!
TIFF-Like PSD supports all PS features
- Very large files (4 time size of PSD)
- Less popular since InDesign now uses
PSD files
!
PDF-Preserves AI and PS features
- Viewable in Acrobat
- Has become preferred file for print
Photoshop Files
!
!
RAW-(nef, cr2 crw file extensions)
!
Raw files are native files produced in digital cameras.
They are not compressed or in anyway altered when
saved. Once edited in PS they should be saved as
PSD or TIFF. The original unedited file is also saved.