Use the Right Size Picture for the Medium
Pictures have power on the page - the power to grab your reader's attention and to convey or enhance your message. Pictures help the reader scan the page and find entry points into the text. They give the reader a quick summary of what the text is about and help the reader gauge his or her interest in diving into it. They also can help a reader quickly grasp complex ideas.
Pictures can relieve the tedium of gray type. But they can also distract the reader from your message if the pictures don't relate closely to the message. Make sure you are in control of your message with the pictures that you use in your publication.
You can change the size and resolution of the graphics that you add, usually with good results. But sometimes a graphic can't be reduced or enlarged enough to fit your needs. That's why it is good to know what you need before you start and find the graphic that is the best match.
Graphics that are created by a paint program, a scanning program, or a digital camera are made up of a grid of differently colored squares called pixels. A picture contains the same amount of information, or number of pixels, whether you scale it larger or smaller in your publication.
The resolution of a picture is expressed in pixels per inch (ppi). You sometimes may see picture resolution expressed as dots per inch (dpi) instead of ppi. These terms are often used interchangeably.
If you want more details to appear as you enlarge your picture, you need to start with a picture that has more pixels, or a higher effective resolution. Enlarging a picture decreases the resolution (fewer ppi). Reducing the dimensions of a picture increases its resolution (more ppi).
If your picture resolution is too low, the picture will have a blocky appearance. If the picture resolution is too high, the file size of the publication becomes unnecessarily large, and it takes more time to open, edit, and print it. Pictures with a resolution higher than 1,000 ppi may not print at all.
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