7. Graphics à la "the Web"
Sending text over the Internet is just old fashioned e-mail. People have been
doing it for decades!
When you can include Pictures, your message can be much more informative!
Is the going rate still 1000 words per picture?
Objectives
After this lesson, you will be able to:
- Identify the graphic formats for the World Wide Web.
- Discuss key points to consider when including graphics in WWW
documents.
- Download a graphic file to your computer.
- Use the correct HTML format for including pictures in your
web page.
Lesson
Lean back and relax! This lesson is mostly an introduction to graphics
for the World Wide Web. But we'll have you do a little activity below.
The Web's Graphic Format
There are numerous file formats for computer graphics. PICT. GIF. TIFF. Not to mentiom EPS, BMP, PCX, JPEG...
It sounds like cryptic poetry. Bad poetry.
The way a web browser displays graphics in HTML format indicates the location of a graphic file in a single format that can be interpreted by different types of computers. For example, when the information in that format is received by your Macintosh computer, the web browser knows to display it as a picture format for Macintosh. However, when that same information is received by your Windows browser, it is displayed as a Windows graphic.
In technical jargon, we would say that this picture format is platform independent. HTML itself is platform independent, since plain text characters can be understood by any computer.
The standard format that can display within a web page is GIF or Graphics Interchange Format. The GIF compresses the picture information (reduces the file size) and translates it to binary code that can be sent over the Internet. GIF compression is most effective on graphics that have contiguous areas of solid color, and compression is even greater when the color is continuous in the horizontal direction.
The other file format used on the web is JPEG (named after the Joint Photographic Expert Group that designed this format). Previously, JPEG images are not displayed in the page but are displayed in a separate window, using an external "helper" application. But most web browsers these days support JPEG images to be displayed right in the web page too.
JPEG compression is very effective for photographic images where the colors can vary spatially over short distances ("grainy" images). JPEG offers some dramatic compression in filesize, sometimes by a factor of 10 (e.g. a 1500 kb file reduced to 150 kb), which may be at a trade-off for some image quality.
For more information about these file formats, see the SITO page on
Graphics File Compression. If you are in the mood for a great book, try Lynda Weinman's Designing Web Graphics
More and more graphics programs have built in features to save files as GIF
format. If not, below are several shareware programs/utilities for performing
the conversion. You can look for them using a site such as
shareware.com.
| A Few Graphics Utilities |
| Macintosh |
Windows |
- GIFConverter
- GraphicConverter
- clip2gif
- PhotoGIF
(plugin for Adobe Photoshop)
|
- WinGif 1.4
- Lview 3.1
- PaintShop Pro
|
Some Points to Consider When Using Graphics
For this tutorial, you do not have to use one of these graphics
programs. We will show you how to save a copy of any image
that you can see on a web page.
However, as you begin to develop your own web pages,
you should become familiar with creating pictures in either GIF or JPEG
format. If your web pages include graphics, consider the following suggestions:
- Large and numerous images may look great on a high end computer,
but they will frustrate users who must wait for images to be sent
over the network. (like how many of us have a Sun SparcStation at home?)
As a suggestion, keep images less than 100k in file size (we aim for less than 50k each). Smaller is even better.
- On a similar note, not all of us have a 21 inch computer monitor!
Keep graphic images no wider than 480 pixels
and no higher than 300 pixels to avoid forcing users to scroll or resize their web browser window.
- Color gradients may look pretty but for GIF images they do not
compress as much as solid color areas and they can sometimes come out "banded"
- Some graphics programs offer options for "no dithering" when converting to GIF -- this can reduce the amount of "noise" in a solid background.
- Many dark tones on Macintosh
computers are not discernible on Windows computers.
- Rather than displaying all of the images on the web page, have
them linked as external images that are downloaded only when a viewer
clicks on a hypertext item (this will be covered later in
lesson 8a and in lesson 8d). If you have numerous pictures to display, try to break the web page into a series of linked pages.
- A single image (e.g. a small "bullet")
can appear several times in a web page with little added delay each time
you use that same image.
- Many web browsers now "cache" images (storing them
on your computer) meaning that using the same file in several
web pages will load them from the viewer's computer rather than
loading them across the Internet.
- Most importantly, make sure that the images are ones that
add meaning to your HTML documents.
You may design a beautiful web page, loaded with large pictures,
that may load nicely from your computer, but may be excruciatingly
slow by a viewer using a slow modem over a busy network. The 'net is a busy place and getting busier every second.
Saving and Including Pictures in Your Web Page
For the next lesson you will first need to download a copy of a GIF
image of an erupting volcano (watch out for that hot lava!).
Just follow the instructions on the Lesson 7 Image Download Center and then return here to complete this lesson.
Check Your Work
Check to see that the file, "lava.gif", is saved in the
same directory/folder as your HTML text file,
"Volc.html". If it is not there, check to see if you
accidentally saved it in another directory/folder. Then, move it to the
correct location.
Review Topics
- What are the two graphic formats used for the World Wide Web?
- How can a graphic file display on different computers?
- What are some key points to consider when including graphics in
web pages?
- How did you save the lava graphic for use in your WWW
document?
Independent Practice
Surf the web and browse for pictures. Try to download at
least one image that might be useful for your page. Just a few places you might try are
Coming Next....
You have the image... Now, how in the HTML do you display it in your
document?
Writing HTML Lesson 7: Graphics à la the Web
©1995, 1996, 1997
Maricopa Center for Learning and Instruction (MCLI)
Maricopa Community Colleges, Arizona
The Internet Connection at MCLI is
Alan Levine --}
Comments to levine@maricopa.edu
URL: http://www.mcli.dist.maricopa.edu/tut/tut7.html