Digital Imagery Tips
Digital
Photography Professional Development class PowerPoint outline
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The following notes about digital imagery were created by Ken Russell. If you have questions about this topic, or would like to see more information about a particular aspect of it, you are welcome to contact him by email.
Think ahead about how you will use an image before you take it:
- If you plan to print the image, you will want to set your digital camera to a higher image resolution that is based on the resolution of the output device (usually a printer).
- If you plan to put the image on the web, you will want to use a low image resolution setting on your digital camera.
- If you want to do both, use a high resolution setting on the camera, then transfer the image file to a computer. Keep the high resolution image for printing and resample a duplicate image to a lower the resolution for use on the web. You will then have both a high and low resolution version of the same image for different purposes.
Image
Resolution
The
term resolution in reference
to images refers to the number
of pixels (points of color) that
compose an image and determine
its detail. Resolution is determined
by the pixel dimensions of the
image—the
number of pixels along the width
and height of an image. The higher
the resolution, the more pixels
the image contains.
Image
Size:
Refers to the
dimensions of the image. It can
be expressed in pixels (for example:
800 x 600 pixels), or by inches.
If it is expressed in
inches, the output resolution must
also be noted. For example, an
800 x 600 pixel image will print
at 2.6" x 2" on a printer that
prints at 300 dots per inch
(800/300 x 600/300). It will print
at 5" x 4" if the printer prints
at 150 dots per inch.
Monitor Resolution
Monitor resolution refers to the
number of pixels that can be
displayed on a monitor. It is
expressed in dots per inch (dpi).
Most monitors are about 72 dots
per inch (dpi), but they can
vary somewhat.
Image File Size:
The higher the resolution, the
larger the file size of an image.
Image file size, usually measured
in kilobytes or megabytes, is
proportional to image size, but
varies depending on the file
format (whether it is a JPEG,
TIFF, etc.). The lower the image
resolution, the more pictures
you can store in the camera.
The higher the image resolution,
the less images you can store.
Camera
megapixel rating—how much
is enough?
How
many megapixels should a digital
camera be rated for in order to
produce a picture of a specific
size? This table shows the megapixels
required for common sizes and
outputs:
(72 dpi) Low-Resolution
Printer (150 dpi) High-Resolution*
Printer (300 dpi) 4" x 6" 0.12 MP 0.54 MP 2.16 MP 5" x 7" 0.18 MP 0.79 MP 3.15 MP 8" x 10" 0.41 MP 1.80 MP 7.20 MP 11" x 14" 0.80 MP 3.47 MP 13.86 MP
Green numbers
indicate images that can be taken
with a 3 megapixel camera.
*There are
even higher resolution printers—600
and even 1200 dpi. 300 dpi is typical
for non-professional
output; 300 dpi looks pretty good.
Digital Camera Suggestions
- To take good digital pictures, you should begin by thoroughly reading the camera's manual.
- Disable the digital zoom, it degrades image quality (the manual zoom doesn't).
- Most digital cameras save images in the JPEG format by default. For high quality printed images, change the file type setting on the camera so the image is saved as TIFF or RAW. However, this will considerably increase the file size. An alternative is to set the JPEG quality high, but there will still be some quality degradation. If you are unsure, run tests at various settings and carefully examine the results from the output device you will be using.
References
Resolving Resolution: www.mkprod.com/ResolvingResolution.htm
About
Resolution: www.ltlimagery.com/resolution.html
