Image scanning is a process which converts images on paper to computer format (GIF, JPEG, etc.). This
is accomplished with a device called a scanner.
20/20 Technologies uses the Hewlett Packard ScanJet 3c. At 2400 dots per inch, combined with millions of colors, this is more than adequate for scanning paper materials for Web page design.
On the Internet, image transfers are the most time consuming process. The reader receives the text of your page in seconds, then has to wait for the images to slowly download. The adage "a picture is worth a thousand words" is an understatement: a large image file may take up the space of 100,000 words!
Do not confuse the size of the image (the physical width and height of the rectangle, measured in inches or pixels) with the size of the file. The file size of an image is a combination of several factors, including:
Large files take a long time to send, and therefore should be avoided. Good Web page designers always are looking for ways to make graphic displays more compact, and avoid graphics that are not necessary to enchance the page's content.
- the width and height of the image, in pixels
- the number of colors used
- the image format used
- the complexity of the image
Images can be scanned in three color modes: black and white, 256 colors, and 16.8 million colors. The more colors used, the longer it takes to transfer across the World Wide Web.
Below are three examples of the same picture, scanned at 16.8 million colors, 256 colors, and B/W, respectively. All three of these images are JPEG's.
There are several factors that can influence how these images look on your screen. Some systems can only display 16 colors, in which case all three of these pictures would look rather poor. A 256 color system will show the first two pictures as being identical. For users with 65,536 or 16.8 million colors, the first picture should look a little better than the other two.
There are dozens of image formats, but only two are widely accepted throughout the Internet. These two are call GIF (pronounced jif) and JPEG (pronounced jay peg).
Advantages of GIFs:
Advantages of JPEGs:
- GIFs are more widely used than JPEG, and a few users do not have JPEG viewing ability.
- GIFs represent an image without loss, whereas JPEGs smoothing techniques create image loss.
- GIFs can be transparent, i.e., the image can appear non-rectangular.
- GIFs can be interlaced, i.e., they load a low-resolution image first then slowly fill in details. Because of this, the file seems to load quicker since the reader has something to watch while it happens.
- GIFs work equally well with line drawings (like cartoons) as with photographs.
In general, 20/20 Technologies uses interlaced GIF images for most jobs, relying on JPEGs for complex photographic images.
- JPEGs smooth out certain regions of the image to provide a compact file which transfers quickly. This is the primary advantage of the JPEG format.
- JPEGs are the best way to store photographic images, but are not recommended for line-art.
The size of the source document does not effect the size of the computer image. This demonstration of
a U.S. five dollar bill shows the intense level of detail that can be accomplished with a scanner.
Notice in the last two frames the microprinted words The United States of America.
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