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Vector and
bitmap images
Objectives: You will be able to:
Vector and bitmap images There are two different types of computer graphic images: vector and bitmap. Vector graphics consist of lines
and curves which are defined by mathematical objects or vectors.
Desktop publishing programs and illustration programs concerned with print
reproduction usually use vector graphics. No matter how you change
the size of a vector graphic, it always maintains its quality as the information
is mathematically recalculated.
Image resolution Computer display screens are made up of
a grid of thousands of pixels. The number of pixels that they can display
per inch or ppi,
gives us the information we need for determining the size or image resolution
our bitmap graphics should have.
Monitor size and settings
Larger monitors will accomodate larger
image sizes, such as 800 by 600 or even 1024 by 768. You can also
change the settings of a computer monitor, which affects the display size.
This will be demonstrated in class.
File size Digital image file sizes are measured in
standard terms: kilobytes
and megabytes.
The more pixels you have in your object, the larger the file size.
File size can be an important consideration when developing a project.
It can determine how fast your images load, how they look and how they
can be manipulated in your program.
Bit resolution/color depth Another factor affecting file size is bit resolution or colour depth , which refers to how much color information, is available for each pixel. Greater pixel depth means more color information available for each pixel. The Internet has certain limitations when
dealing with color, and I have tried to approximate the effects of using
various bit depths here. Assuming that the images below would be
640 by 480 pixels in size, here are representations of image quality and
file size:
Image file formats The more popular file formats that we will be dealing with include: BMP – a standardized and reliable format to use, especially between platforms. Supports color depths of 1 to 24 bit. GIF – limited to 256 colors or less. A poor choice for large images or photographs. Very popular for small web graphics and animations. GIF89a – limited to 255 colors or less. Provides transparency features. Popular for web graphics and animations. PSD – this is a raw, proprietary Photoshop format that usually cannot be applied to any other program until it is “flattened” and saved in a common format. PICT – a reliable format primarily used on the MacIntosh and also supported in some PC programs. TIFF – an older format becoming less popular for multimedia work but still used extensively in desktop publishing. File sizes are typically large, as it is an excellent file format for printing high quality photographic images. Quite often incompatible between platforms or programs. JPEG – a very common image format for photographic images. It can maintain a reasonably high quality image with many colors while still compressing file size (the amount of compression is flexible). There is always some image degradation with this lossy format and image quality can decrease with size or resizing. PNG – a new format which is lossless but not very popular at the moment. It incorporates a transparency feature and may someday replace GIF in popularity for web graphics. AVI - the video and animation standard for Windows. QT (Quicktime) - a very good cross-platform movie standard for Macintosh and Windows. *Remember that Windows requires a file extension after the file name - i.e. photo.bmp For more information on these and other file formats, visit the following sites: The Kodak Digital Learning Centre Martin
Reddy's graphics file formats site at U. of Edinburgh
Palettes
Conversions and resizing There are many excellent programs available that allow you to convert one file type to another. One of the easiest ways to do this is to open the original file in Photoshop, then re-save it in the new format you require. The thing to be on the lookout for is ppi and resizing. We have already seen an example of what can happen when you increase the size of a bitmap image. Some programs such as Hyperstudio, will
import and automatically convert and even resize a variety of image formats.
Scanning Scan resolution is virtually the same as image resolution. Different software provides various ways for you to select the proper size required for a specific application. Read this article
from Barnard
College on image scanning.
Importing clip art from the World Wide Web
A Word on Copyright There is much information available on
the Internet. This includes textual information as well as audio, photographs,
graphics and other images. It is important for you to realize that these
things are usually the property of someone else, and using information
or materials that belong to someone else can be an infringement of copyright,
and against the law. For more information on copyright, visit: A
Brief Introduction to Copyright - by Brad Templeton.
Using Images in Hyperstudio As you have discovered, Hyperstudio has
its own drawing tools that you can use to create pages. You can create
all of your pages in Hyperstudio, or you can create them in part or whole
in another program (such as Photoshop) and import them into Hyperstudio
as a background or a graphic object. Hyperstudio will accept most
popular formats including bmp, jpeg, tiff and pict files.
Things to do
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Michael Shaw, 1997
