Optimizing Resolution
An image file's resolution determines the size of its pixels: the higher the resolution, the smaller the pixels and therefore the sharper the image. The more pixels you have, however, the heavier the image becomes, and the longer it takes to download.In the world of print graphics, higher resolution is almost always better than lower resolution. But in Web graphics, the display capability of monitor screens puts a tight constraint on image resolution. Windows monitors display at 96 ppi (pixels per inch), which is actually fairly low-res. Macintosh monitors are even lower, at 72 ppi. In the spirit of cross-platform compatibility, the resolution of 72 ppi has emerged as the standard for Web images, even though the vast majority of monitors can display at the slightly higher benchmark of 96 ppi.
GEEKSPEAKThe resolution of an image file determines the size of its pixels: the higher the resolution, the smaller the pixels and the sharper the image. |
Figure 28.1. The image on the left has a resolution of 600 ppi, while the image on the right has a resolution of 72 ppimore than eight times lower. However, both look exactly the same on screen, since monitors are relatively low-res output devices.
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TIPImages that you specifically intend for your visitors to print out should be optimized for print instead of the screen. But not everyone who visits your site will print out these images. To improve the performance of your site, don't build the high-res images into your pages. Use low-res, screen-optimized images instead, and include links to high-res, print-quality images for those who want them. The high-res images won't look any different on screen, but they'll translate much better to print than their low-res counterparts will. |