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Image
formats for the Web
also useful for email, PowerPoint, inserting in Word
documents
Cynthia
Beth Rubin
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| GIF
and JPEG are both standard, small, compressions
Instructions
on saving to these formats in Adobe Photoshop and ImageReady
are here
Standard
Formats are needed when:
- Uploading
to the Web.
- Sending
email to some one with limited software (and limited time)
- When
you do not know the limitations of a particular software
Compressed
Formats are needed when:
- Uploading
to the Web.
- Sending
normal email (special collaborations are exceptions)
- When
disk space is limited, and image quality is not critical
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Why
use a GIF?
- A GIF
is an 8 bit image (256 colors or less). This makes it a good
format for images with few colors.
- Only
a GIF can be animated with standard software (not using
Flash)
- The fewer
colors that a GIF has, the smaller the file size (generally).
- The advantage
of a GIF is that the artist does all of the file reduction.
What you see when you are done reducing is exactly what you
get.
- A GIF
can have "transparent" as one of its colors
- A GIF
can be made up of any 256 or fewer colors, but only 216 colors
are Web safe (will look the same on all computers)
- To read
more about Web safe palettes Lynda
Weiman's page. You can download charts of safe colors
from her site.
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18 web colors, dithered |
 18
selective colors, no dither |
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| Why
use a JPEG?
- A JPEG
uses the full range of thousands of colors. This makes
it the best format for images with many colors.
- A JPEG
is a "lossy" compression. The more detail that is
lost, the smaller the file size. Thus the scale in quality
for jpegs.
- Blurred
images compress better than sharp ones.
- Low contrast,
and less saturated images compress better.
- The advantage
of a JPEG is that subtle tones can be preserved.
- A JPEG
which is viewed on an 8 bit monitor (256 colors) will be dithered
as it is displayed.
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jpeg
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