(Shelly Cashman Series) Gary B. Shelly, H. Albert Napier, Ollie N. Rivers-Web design_ introductory concepts and techniques -Cengage Learning (2008)

Image File Formats 145
Q&A
What are the Camera
Raw (RAW) and
Scalable Vector
Graphics (SVG)
image formats?
A RAW image format is
the raw data or “digital
negative” recorded
by a digital camera;
RAW image formats
might vary by camera
manufacturer. Scalable
Vector Graphics (SVG) is
a vector image format
developed by the W3C
for XML documents;
SVG might play a
greater role in Web
page images in the
future.
Figure 5-15 The JPEG image file format is appropriate for photographs or
photo-like art.
A progressive JPEG is similar to an interlaced GIF and appears on the screen in
a sequence of passes with progressively improved image quality, allowing the viewer a
preview of the image. You can specify the number of passes in a progressive JPEG. Like
interlaced GIFs, progressive JPEGs might be suitable if your target audience is using slow
dial-up Internet access and you want them to be able to preview a lower-quality image
before the higher-quality image completely downloads in the browser. However, at
broadband access speeds, progressive JPEG images lose their usefulness.
Use the GIF image format for basic, solid-color images that do not require more
than 256 colors, such as cartoons, diagrams, and navigation buttons. Use the JPEG
image format for photographs or art-like images.
DESIGN
TIP
Portable Network Graphics Format (PNG)
As the popularity of GIF images on the Web grew, CompuServe and Unisys, the
company that developed the technology used to compress GIFs, announced that anyone
using GIF images had to pay a license fee for doing so. The Portable Network Graphics
(PNG) image format was developed as a free open source image format to replace the
GIF format. (Note that the Unisys compression patents expired in 2004; license fees for
using GIFs are no longer required.) The PNG format is superior to the GIF format in
two primary ways:
• Greater range of colors than the GIF format; the PNG format supports more than
16 million colors
• Superior transparency capabilities
Whether PNG images will replace GIF images for Web images is still largely
undecided. Lack of browser support for PNG has been a major reason that designers
have chosen not to use PNG images in the past; however, current versions of today’s most
popular browsers do provide support for the PNG format.