Choosing the best Graphic Format for the Job
If you've ever wondered why the formats of
graphics on the Web are different from those used in documents, presentations,
or spreadsheets, you're not alone. With TIFFs, GIFS, BMPs, and PNGs, it's hard
to know which format to use, and which program to use it with. Knowing what
formats are out there, and learning about the advantages and disadvantages of
each can help you create lively documents, presentations, and Web pages.
Popular raster graphic formats
BMP (bitmap), GIF (Graphics Interchange Format),
JPEG (Joint Photographic Experts Group), PNG (Portable Network Graphics), and
TIFF (Tagged Image File Format) are raster image formats. A raster image is also
known as a bitmap and is created from rows of small dots called pixels
("picture elements") or "bits." Because a raster format uses
a fixed method of specifying an image, the image cannot always be immediately
rescaled without losing definition.
Bitmap (BMP)
The Microsoft Windows BMP format (.bmp file
extension) can display millions of colors. Because it is supported by several
programs, it is an extremely practical file format to use when you are providing
an image to someone who may not have the program in which you created the image.
Graphics Interchange Format (GIF)
The GIF format (.gif file extension) is one of
the two most common file formats for images on the World Wide Web, since it is
supported by almost all Web browsers. Because this format can only display a
maximum of 256 colors, it is best used for black-and-white line drawings, color
clip art, and pictures with large blocks of solid colors. The GIF89a format also
supports both transparency and animation. Use GIF files for:
- Images that contain transparent areas.
- A limited number of colors, such as 256 or
less.
- Colors in discrete areas.
- Black and white images.
- A small-size image, such as a button on a
site.
- Images in which sharpness and edge clarity are
important, such as line drawings or cartoons.
- Images containing text.
- Animations.
Joint Photographic Experts Group (JPEG)
The JPEG format (.jpg or .jpeg file extension) is
the other most common file format for images on the Web. It is not limited to
256 colors, so you can use it to display high-quality photographs, or pictures
containing millions of colors. Because it is designed as an image storage
format, it can efficiently compress large, high-quality photos into very compact
files, so it is very useful when you want to send a large image in e-mail.
However, the more you reduce your image's file size (or modify and re-save the
image), the more image information is discarded — and quality is decreased.
Moreover, this format does not support transparency or animation. Use JPEG files
for:
- Photographs.
- Natural-looking images.
- A large number of colors, such as in the
millions.
- A great deal of detail, such as a photograph
of a house on a real estate site.
- An image with large dimensions.
Portable Network Graphics (PNG)
The PNG format (.png file extension) can display
millions of colors. Because it is such a new format, however, fewer browsers
currently support it (although it is quickly gaining support). Images saved in
this format will not degrade in quality, even if the file is compressed. It
supports transparency, but it does not support animation, since it cannot
contain multiple images.
Tagged Image File Format (TIFF)
The TIFF format (.tif or .tiff file extension)
produces very high quality images and is therefore used in publishing
quite often. It can display millions of colors (although grayscale images are
limited to 256 colors or shades), and typically results in larger image
files than the GIF or JPEG formats. If you plan to edit an image in a
program other than the one in which you created it, saving it in this format is
helpful, since it is widely recognized by various programs.
The most common graphic file formats that
Office supports
| Program |
BMP |
EMF |
EPS |
GIF |
JPEG |
PNG |
TIFF |
TGA |
WMF |
| Microsoft Word |
X |
X |
X |
X |
X |
X |
X |
|
X |
| Microsoft Excel |
X
|
X |
|
X |
|
X |
|
|
X |
| Microsoft FrontPage® |
X |
X |
X |
X |
X |
X |
X |
X |
X |
| Microsoft PowerPoint® |
X |
X |
|
X |
X |
X |
X |
X |
X |
Note Depending
upon the program you're using, you'll need a graphics filter installed to
insert any other graphic file formats. If you didn't install the filter when you
installed Office or your specific Office program, you can run the setup program
again and add the graphics filter. For more information about graphics filters,
see Help for your particular program.
Figure out the best file format for your task
When you save your document, data and workbooks,
or presentation as a Web page in Hypertext Markup Language (HTML) format, all
graphics (including drawing objects and pictures) are saved in GIF, JPEG, or PNG
format so that they can be viewed in a Web browser.
If you reopen the Web page in Word, Excel, or
PowerPoint, the graphics will be in their original file formats so that you can
still edit them as you normally would.
|
Action |
BMP |
GIF |
JPEG |
PNG |
TIFF |
| Post an image on a Web page |
|
X |
X |
|
|
| Export easily to other
computer imaging programs |
X
|
|
|
|
X |
| Compress a large image to
create a small file to send in e-mail |
|
X |
X |
|
|
| Use transparent areas in
images |
|
X |
|
X |
|
| Create animation files |
|
X |
|
|
|
| Decompress images without loss
of quality |
|
X |
|
X |
|
| Create highest quality images
(for publishing, etc.) |
|
|
|
|
X |
| Display millions of colors in
an image |
X |
|
X |
X |
X |
| Retain image quality through
numerous saves |
X |
X |
|
X |
X |
Note The formats that are generally used
for Web pages are GIF and JPEG. When you add a graphic other than a GIF or
JPEG to a page and then save it, FrontPage automatically converts the graphic to
a GIF if it has 8 bits of color or less, or to a JPEG if it has more than 8 bits
of color.
|
