Page 317 - Enhancing CAD Drawings with Photoshop

4386.book Page 301 Monday, November 15, 2004 3:27 PM
E-MAILING IMAGES 301

Figure 9.13
The 4-Up tab in the Save
For Web dialog box

TIP If your e-mail recipient is technologically savvy, post a high-res image on your FTP site and have
them download it. Exchanging data is a nonissue with technical people.

Choosing a Compression Format
The Save For Web dialog box allows you to compress images in three major graphics formats: Graphics
Interchange Format (GIF), Portable Network Graphics (PNG), and Joint Photographic Experts Group (JPEG
or JPG). Each format has its strengths and weaknesses:
GIF images are best for images with a few flat colors, such as pictures of text or simple graphics. GIF
images use Lempel-Zif-Welch (LZW) lossless compression, so there is no degradation in image quality
and small file size. GIF images can be compressed more by including fewer indexed colors. In addi-
tion, GIF images can preserve transparency but not alpha channels. Note that the GIF image format is
proprietary.
PNG images were developed as a free alternative to GIF. Lossless PNG images are superior to GIF, es-
pecially in the 24-bit version that supports greater color depth and anti-aliased transparency. Older
browsers do not support PNG images so it is a judgment call to use these images as you may be exclud-
ing some people.
JPEG images are best used to display photographs or other continuous tone images on the Web. They
use lossy compression that sacrifices image quality for smaller file size. Highly compressed JPEG files
have smaller sizes and lower image quality.