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Photos on the Web One of the best parts of creating personal Web pages is the opportunity to post family snapshots and other images that interest you. Unfortunately, digital imaging devices can produce very large image files. Since dial-up modems download large Web pages very slowly, you will usually need to limit the size of your image files. You can generally post both .JPG and .GIF files to a Web site, but the .JPG format usually is much better for photos. For this reason, we mostly discuss .JPG files here. What is a Digital Image Made Of? A full color digital image consists of many individual colored dots, called "pixels," laid out in squares on a grid. Your computer monitor's grid is similar to the points of light you see when you look very closely at a television screen. The grid has dimensions of width and height, which may be displaying 640 by 480, 800 by 600, or a higher numbers of pixels. Scanners and digital cameras all have different ways in which they capture and store images in files on your hard drive. For example, Kodak Photo CDs and Picture CDs/Disks, and Internet photo download services (such as Kodak's PhotoNet), deliver different image file formats and sizes. Scanners, like color printers, digitize at specific resolutions, given by dots per inch or "dpi." If you scan a 5" x 7" color photo at 600 dpi, the file you produce will be huge: 4,200 pixels wide by 3,000 pixels high, taking up 36 megabytes of memory. Such an image would take 2 hours to download via a 56K modem and require 36 browser windows to view! This extreme example highlights the pitfalls of using high-resolution, uncompressed color images in Web pages. Fortunately, most digital cameras and photo media (but not Kodak's Photo CD) store images in a compressed format known as JPEG. JPEG greatly reduces image file sizes but preserves the widths and heights of images. However, while JPEG files are supported by all Web browsers, the highest-quality JPEG images may be too large to download and view quickly. How to Minimize File Size
Photo editing and Web page software from Microsoft (Photo Editor, Photo Draw, Picture It!, Front Page), Adobe (Photo Deluxe, Photoshop, Page Mill), and others can help you reduce the sizes of your image files. All of these programs open a variety of file formats including BMP, TIFF, GIF and JPEG, allow you to change an image's dimensions and quality, and save the file in JPEG format. Quality is directly related to compression: the more you reduce the file size of your image, the worse the image looks. Extreme JPEG compression introduces flaws such as fuzziness, streaking and blocking, especially in areas of high contrast or sharp edges. Different programs specify the ranges for JPEG compression using various terminology:
Experiment with your program and images to find the best balance between file size and quality. Another way to reduce file size is to reduce the image dimensions. By decreasing the width and height in pixels or inches, or the resolution in dpi, you will get a smaller image with less detail, but without introducing fuzziness and the like. Be aware that a JPEG file doesn't keep track of the original dimensions of your image in inches. For instance, your image editing software may differentiate between a 4" by 6" photo at 75 dpi and a 2" by 3" image at 150 dpi, but the resulting JPEG file will be the same, and it will appear in your browser at 450 by 300 screen pixels. The actual displayed size in inches of the file you view depends upon the physical size and resolution setting of your computer monitor, not the original image. Some Sample Scenarios
To assist you in planning the sizes of your image files, here is a helpful table. It compares file sizes with download times. For example, you create a Web page with ten 50 Kilobyte images. The total time to display the page with a 28.8 Kbps modem will be three minutes, plus the time needed to contact the Web site, download the rest of the page and draw the images. Sometimes pictures are worth more than words -- see our sample images.
* Assumes an FCC-mandated maximum receive speed of 5300 bytes per second.
Image Editing Links Here is a list of digital image editing programs under $100, many under $50, including some demos and shareware:
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