Technology
Digital Imaging

 

This section covers the fundamentals of dealing with resolutions, understanding digital image formats, and help when editing a digital image.


  • Digital Imaging Basics
  • Fine-Tuning your Image for Posting on a Web Site

Graphics: Digital Imaging

Digital Imaging

One of the best ways of getting information across to your audience is by incorporating the use of images in your talks and programs. The adage that "a picture is worth 1000 words" is very true in today's society. Visualize your ideas. Use photos to bring "real world" examples to the public. Show a trend by using a graph. Reinforce your talks with visual examples.

This section is designed to give you instruction on converting slides, photos, drawings, and other "physical" images into a digital format for use with various computer presentation programs.


 

Digital Image Basics

You can use scanners and digital cameras to incorporate images into the work you do.  To use images effectively you need to understand some basics about digital images.  Resolution, color depth, and file format are critical elements when using digital images.  First, we will cover the basic terminology and then apply that to using scanners and digital cameras.

 

 

Resolution Choosing a Resolution
Resolution affects the amount of discernible fine detail
in an image.  A low resolution image looks coarse.  
A high resolution image looks smooth.  
It is like comparing burlap to silk.

Computer images are made of dots.  The more dots per inch (dpi), the higher the resolution.  Printers range from 300 dpi to 2400 dpi.  Check your printer specifications to find its resolution.  On the computer screen, the dots are called pixels.  We generally use dots per inch and pixels per inch (ppi) interchangeably.  Monitor resolution is usually around 70 to 100 dpi.

A high resolution image is made of more tightly packed together dots.  More dots in the image means a larger file is created.

Color depth Color Depth
Color depth refers to the number of colors that can be displayed by each pixel.  In the computer world, that relates to the bits of information that are stored about the color of each dot or pixel that makes up the image.  True color (32 bit) can store millions of bits of color information per pixel.  The next step down is 24 bit color which is still millions of colors.  Next is 256 colors (8 bit) and then, black and white (1bit).

The more bits you store, the larger the file.  So if you are scanning an image that is only made of black lines on white paper, you should not use the true color (32bit) setting because the file will be much larger that it needs to be.

File Formats File Formats
There are three common graphic file formats-TIFF (tif file extension), GIF (gif), and JPEG (jpg).  The Web uses JPEG, GIF, PNG and new file type (released April 2001) called SVG (Scalable Vector Graphic).  You also might also use BMP image files. BMP's are Windows Bitmaps and are a common Windows image file format.  You can find thorough explanations of each file type on the web.  We are going to cover the basics. 

To make files smaller, compression can be used.  Lossless compression saves the data and packs it more tightly together.   The other option is to lose some data when the file is compressed.  JPEG uses this lossy (rhymes with bossy) compression to achieve very small file size.  The more you compress a JPEG, the lower the image quality.

TIFF or TIF
TIF is a good format for master copies of images.  It is widely supported by image editing software.  It uses lossless compression which means when a TIFF file is saved, no image information is thrown out.  This also means the files can be large.

GIF (pronounced "Jif" or "Gif")
GIF format is best for saving images with few colors.  GIF can store and yield up to 256 colors.  This works best for something like our K-State Research and Extension Logo.  GIF files are smaller than TIFF and higher quality than JPEG if the image contains few colors.  GIF is not an appropriate file type for storing photographic images.  GIF files are viewable in web browsers and GIF is common format for web icons and clipart.

JPEG or JPG (pronounced "Jay-Peg")
The JPEG format is the king of compression.  JPG is the most common format for viewing images on the Web. JPEG images are small for fast delivery over the Web and are also the most common format saved in digital cameras. A word of caution, don't save JPG's over and over because the images get compressed over each other and lose significant amounts of image detail and information.  JPEG uses lossy compression.  The good news is that a high quality JPEG is often 1/10 the size of a TIFF.  If you are going to send an image via e-mail, it should be as small as possible without affecting image quality. 

Avoid opening and saving a JPEG file multiple times since a JPEG file loses some quality each time.  It is a bit like making a video tape copy from a copy.  Every generation is of lower quality.  If you will be editing an image, don't save your master or archive as JPEG.  If you need to edit an image, save the intermediate image as TIFF.  If you want a master copy, keep it in TIFF and you can always save a JPEG file later for email or for placing on a web page.

More information on Web Formats:
  W3 standards

 


When was the last time you calibrated your monitor?
Monitors change color and brightness over time. There are several tools available to calibrate what you see on your monitor so it matches your digital images for print, computer presentations, and the Web.
If you own Adobe Photoshop, use the Adobe Gamma program located in the Control Panel. More info. .
Free Internet Monitor Color Calibration at
EasyRGB

 

What's Your Output?

 

Your Use

PPI/DPI

Suggested File Format

Computer presentation
(Power Point, Presentations, etc)
100 JPG for smaller file size
BMP for better quality
35mm Slide: 900x600pixels
PPT Full Screen: 1024x768pixels
WWW web page
(CMS, HTML editing)
72 GIF, JPG, PNG, new SVG
GIF used for clipart, logos, or text
JPG used for photographs
PNG good for saving images repeatedly
Laser Jet Printed
(Desktop publishing, brochure, flyer)
200 to 300 TIF or BMP
Material to be photocopied 200 to 300 TIF or BMP
High quality publication
(professional journal, published book)
600 TIF or BMP
Large poster
(20" X 24" or larger)
150 TIF or BMP