Understanding Graphics
Overview
The size of graphics are measured in dots. The required density of these dots depends on where the image will appear. On a computer screen, we call those dots pixels. (Abbreviated px below.)
| Low Resolution | Medium Resolution | High Resolution | |
|---|---|---|---|
| Media | Internet (Web page or email) |
Newspaper | Magazine, Ink-Jet Printer, Brochure |
| DPI (dots per inch) |
72 - 96 approx (depends on monitor) |
150 | 300 |
| How big will a 300px wide image print | Over 3" wide | 2" wide | 1" wide |
How to tell how many pixels wide an image is
On a web page, right click on an image and select "View Image Info" in Firefox or select "Properties" in Internet Explorer. So, for example, the BBB image to the left is 101px wide. If you used this graphic image in a brochure, it would be 1/3" wide. High-resolution printing requires more dense dots or pixels.
You've probably noticed that we're only talking about image widths. Most media has more latitute for height. Web pages can scroll up and down and printed pages can flow onto the another page. But you don't want sometime to be wider than your computer screen and certaintly not wider than the printed page.
Two types of graphics, Vector and Bitmap
Vector? Bitmap? What's that?
See Bitmap (or Raster) and Vector in Wikipedia
In a nutshell, bitmap images are a bunch of dots. If you blow up the image, the dots get bigger and the image looks pixelated. (horrible) All photographs are bitmap images.
 |
 |
| A bitmap star that's 38 px wide | Portion of same star blown up to 1090 px wide |
Vector images are curves (or angles). If you blow up the image, the curves get bigger, but no matter how big you blow it up, it will be an exact replica of the original. Your logo is likely to be a vector image in its native format, that is, the format of the software used to create it.
|
 |
| A vector star that's 38 px wide | Portion of same star blown up to 1090 px wide |
About your logo
Here's a word of warning. Keep the original copy of your logo in a save place. Let's say you decide to print a banner or poster with your logo on it. If you can your logo as a vector image, you can blow it up to the size of the Goodyear blimp and it will look perfect. If you lose your original copy of your logo and try to blow up a bitmap version of your logo, it will look absolutely horrible.
Types of bitmap images for the Internet- jpg and gif
Most images on web pages are either jpg or gif images. In a nutshell, photographs are usually jpg images and logos are usually gif images. For example, right click on the header of this page and look at the properties or image info. You'll see the filename is topimage-bg.jpg. It's a photograph of a chart. Right click on the BBB logo to the left. You'll see the filename is accred_bus_7469.gif. It's a logo, so likely to be a gif file. The difference between a jpg and a gif image has to do with how the image is compressed. With a gif file, unused colors are discarded. So with the BBB logo, the file will only contain white and shades of blue. But you don't want to discard colors for a photograph, so jpg images are compressed differently.
Frankly, if you find this confusing, don't sweat it. It's not crucial.
Images for hi-resolution printing
Photographs
A printer will want photographs 300 dpi (dots per inch), so if you want to print an image that will be four inches wide, you'll need an image that's 1200 px wide. There's a good chance you will have someone else handle your printing design and layout, so here's the most important thing you need to know: Keep the original copy of photographs, whether from a digital camera or downloaded from the Internet. Keep the original. You can always shrink it down. You can't blow it up--it just gets "pixely." (Like the bitmap star above after it's blown up.)
The best images you can give a graphic artist are the photos straight from the camera--not modified at all. Or for logos, the best image you can give a graphic artist if the logo in a vector format. Then it can be resized to any size at all.
Action Plan
None, you're done!
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