Small graphics saved from the web usually print poorly (resolution is too low).
Use a photo editing program to resize photos, scans and web graphics; don't drag or scale them.
Use images at the appropriate resolution; balance quality vs. file size.
File size: big photo + high resolution = HUGE files.
Most digital camera photos are much bigger than you will ever need; resize them before pasting or sharing.
Vector = lines and shapes you can edit individually (.eps, .ai). Raster = groups of pixels like a photo or web graphic (.jpg, .gif)
It’s easy to add impact to your documents or web site by adding images. There are a few things to know before you design a document with images. This newsletter outlines some of the broad technical basics of working with electronic images.
Importing an Image
Most word processors and publishing programs allow you to import images. Just look for a command called “insert,” “import” or “place” (you may need to load filters from your program disk to import certain file types). Many programs give you two import options:
- “Link” to the image file if you want the document to automatically show changes you make later to the image file.
- Save a copy of the image file in your document; this creates a larger file, but is helpful if you plan to move the document or share it with other users.
Keep in mind that your document’s file size will increase after importing an image, especially if you’re not linking. Some programs create enormous files when you add a very small image, so keep an eye on your file size.
Two Types of Image File Formats
When publishing documents, it helps to know something about the types of graphic files you’re working with. Here’s a quick overview of the different types of image files.
Programs that draw shapes, lines and curves (such as Illustrator) create vector files. Vector images can be resized by dragging or scaling without affecting the printed quality of the image. Vector files include .ai, .cdr, .dwg, .eps, .wmf and others. WMFs can sometimes cause problems in non-Microsoft programs, but work great in Word. If you can use a vector file format in your document, you will benefit from a smaller file size and the ability to resize it easily.
Photos and scanned images are examples of raster images. Image-editing programs that manipulate pixels using paintbrushes and erasers (such as PhotoShop) create raster (bitmap) files. Common raster file types include .jpg, .gif, and .png, which were created for use on the web. Other types of raster files include .tif, .bmp, PICT files and photo CD files. Raster images should not be scaled by dragging.
Photos and Resolution
Always try to shoot/scan an image at its final printed size and resolution. If you are unsure about how large the final image will need to be, shoot/scan it bigger, then reduce the image in a program like PhotoShop before you import it.
- If you enlarge a photo (raster image) in your publishing program by dragging/scaling, it will decrease in quality (a little or a lot).
- If you shrink a raster image by dragging/scaling, you will end up with a file that’s much larger than you need, and maybe too big to email.
- Don’t copy small images from the web and use them as-is in a printed document; a 72 ppi web image will print very poorly. If you use web images, make sure to use the search tools to find images with size of “large.” These images may be large enough to print okay.
File Formats for Web Graphics
The two most common types of web images are JPEG and GIF (pronounced like the peanut butter). These file types were created specifically to make very small files that download quickly. Both JPEGs and GIFS are raster files, so the file size depends on the resolution and the physical dimensions of the image.
- When preparing images for the web, save them at 72 ppi. Any higher resolution will create a much larger file without improving the appearance.
- Choose GIF format for solid colors (logos, charts, etc.). Use JPEG for photos and other images with shading or subtle color changes. Never resave a JPEG as a JPEG; the quality will degrade each time you save it.