Images for a Home Page

by Barbara Christopher



Digitizing an Image

Graphics really make a home page come to life on the World Wide Web. Photos, icons, and drawings in black and white or color can all be used once they have been digitized. This is the process that will turn the image into code that can be stored on a disk. Later software can translate the code back into dots (pixels) that will form the picture on the screen.

Scanners

Scanners are the machines that do the original digitizing of the picture. The best image quality comes from flatbed scanners and one of the best of those is the Hewlitt Packard Scan Jet II (about $900 in 1996.) One with less quality but a more reasonable price is Storm's Easy Photo Reader (close to $250 in 1996.) This machine lets you feed photos into a slot.

To understand the differences in quality and file size (the better the quality, the larger the file) look at the full size versions of the images below.

The picture to the right was scanned with an Easy Photo Reader.

The picture to the left was scanned with
an HP Scan Jet II .



The image quality and the size of the file varied because not only were the scanners different, the resolution settings.were different.


Resolution

Resolution is the ability of a scanner to resolve detail. This is most often measured in dots per inch (dpi.) Generally, as the number of dots increase, so does quality and the size of the image file. The drummers were scanned at 150 dpi with a file size of 70K. The students on the bus were scanned at 50 dpi with file size of 27K. The smaller the size of the file, the faster it will load on your home page. For quickest loading, the images should be scanned at 72 dpi and the final file size be no larger than 30K.

Image Editing Software

Once the scanner has digitized the image, it can be loaded into an image editor. Adobe Photoshop is probably the best of these programs. Some shareware editors are Paint Shop Pro and LView Pro for Windows and GraphicConverter for Macintosh. Among other things, these programs can enhance the original picture, crop the image, and reduce the overall size of the picture. Finally, they can save the image in a variety of file formats

File Formats

The 2 file formats most often used on the World Wide Web are GIF and JPEG. GIF (Graphics Interchange Format) was developed by CompuServe and should be used when there are only a few colors needed in the picture. JPEG (Joint Photographic Experts Group) gives a larger file, but can give you more colors.


This page was developed through GirlTECH '97, a teacher training and student technology council program sponsored by the Center for Research on Parallel Computation (CRPC) a National Science Foundation Science and Technology Center. Copyright June,1997 Barbara Christopher

Comments and suggestions ?

URL for this page is:
http://teachertech.rice.edu/Materials/images.html