Using images and photographs in email, on the web, and in other electronic presentations

Cassidy Sterling

Digital photography has made taking snapshots less expensive than ever before. That doesn't mean that the cameras themselves are cheaper; but one no longer has to buy film or have the film developed. This is a great savings. There are several important facts that you should know so that, once you have taken a nice picture, it remains usable for print, the web, and emailing. It is important is to develop some understanding of the various kinds of image files that are used to save a digital photograph.

Raster Versus Vector Images

There are two ways that a computer can recreate an image.

1. In print: Photographs are made up of tiny dots in color their are usually four colors which include Cyan (C, the color of the blue sky), megenta (M), yellow (Y), and black (black is represented by the letter K). This is called CMYK color.
2. Computer monitor: Images on a computer monitor are also made up of coloured dots except that, because these dots are made of light instead of ink, they work somewhat differently and black, which is the absence of light, is not used. The coloured dots on a computer monitor are called pixels. The colors of the dots are Red (R), Green (G), and Blue (B). This is called RGB color.

Raster and Vector: A computer can understand an image in two ways. The first is that it simply records all the pixels. This is called a raster image. The second way computer can record an image is to remember the shape of the areas of colour and which colour that is supposed to fill that shape. The computer remembers an outline and the colour that fills it. This kind of image is called a vector image.

Images that are recorded in JPEG and TIFF (.jpg and .tif) format are raster images. This is the kind of image that a digital camera makes.

EPS, Adobe Illustrator files, and some others are examples of vector images.

GIF and PNG files (.gif and .png) are hybrid methods of image storage that take advantage of both modes.

The reason it is important to understand the kinds of files that are possible is that it makes a big difference in how your pictures will look and how big the file size will be. JPEG, GIF, and PNG are all modes that compress the image so that it takes up less memory. Smaller files are very good for emailing and putting on a website; however, every time you compress an image, you lose information. If, for instance, you save an image in jpeg format, then open it and make some changes — like cropping it, for instance — and then save the image again, you lose information. The first time you do this, you may not notice much difference, but if you do it two or three times, you will find that the quality of the image has deteriorated quite a lot.

Here are two examples of the same image. The first is the original, the second has been resaved several times:


The second picture doesn't look too bad, but if you printed it, it would look very fuzzy.

JPEG images and image size

Digital cameras almost all create images in JPEG format. This is a good format for sending pictures over the internet. But, be careful because, when you make changes to pictures and re-save them, the quality of the image will deteriorate each time.

The size on your computer monitor of a JPEG image is measured in pixels. A good size for a picture that is going on a website might be less than 400 pixels in width. (Pictures on this website are generally 250 px wide.) However, a good size for a picture that will be printed out would be 1200 X 1500 pixels, or even larger. If you tried to expand an image that was 250 px wide to a similar size printed on paper, you would find that it would look quite out of focus.

You could use a picture 1200 X 1500 pixels in an email or on a web page, but it's not a good idea. Such an image would have a total of almost two million pixels, whereas one that is 400 X 500 pixels is only 20,000 pixels. You can see that the size of the image file can become very large. A large file is very slow to send by email or to view on a web page. Nevertheless, when you send picture of your projects to the SDIA office or to anyone who will be using them for publications, you should send pictures that are as large as possible so that they will be useful in all modes. After all, you can always reduce the size of an image, but you can't increase it.

If you are sending large files to someone who can't receive them in his or her email box because the images are too large, you can use an online service such as www.mediafire.com. This service is free and allows you to store large files. You can then send just the link to the person receiving the file. He or she can download the file when it is convenient, without having to use his or her email service.