Graphics Programs Reference
In-Depth Information
lots of colors blending into each other, soft shadows, and so on.
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PNG.
PNG, which stands for Portable Network Graphics, features lossless
compression. While I most often use JPEGs for on-screen presentations in
slideware, I do occasionally use the PNG (.png) format to achieve a transparency
effect, such as that shown in the slides examples here.
The images in these slides are PNG files. I created the gradient transparency effect in Photoshop. PNG and
TIFF formats can be used for these kinds of transparency effects. (Images in slides from
iStockphoto.com
.)
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TIFF.
If you need to print images, I recommend the TIFF format (.tif), which stands
for Tagged Image File Format. Use TIFF files for printing images in CMYK. (TIFF
files can include an alpha channel for transparency effects and can work in
slideware, but the TIFF files are much larger than PNG files.) TIFF files can be
compressed without losing picture quality. However, compared to JPEGs, TIFF files
can be much larger. Larger file sizes will not usually create problems, especially with
newer computers, but there is no reason to create unnecessarily large files. On
older computers, larger image files can slow things down a bit.
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GIF.
GIF, which stands for Graphics Interchange Format, is a file format used
mainly for the Web. The GIF format may be appropriate for line art with very sharp
edges and large areas of the same color. GIF reduces the colors in an image down
to 256, so it is not good for photographs.
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EPS.
EPS stands for Encapsulated PostScript. You may run into the EPS format
when you purchase line art or vector graphics or create your own line drawings in an
application such as Adobe Illustrator. An EPS file can hold photographic information
as well, but you are most likely to see this format used for vector graphics. The
advantage of vector graphics is that you can greatly increase the image scale
without decreasing the image quality. To illustrate this, I took a vector graphic from
iStockphoto and converted a copy of it to a small bitmap (JPEG) image. When I
stretch the bitmap image larger, you see the quality is reduced as the pixels get
larger. The vector image, however, looks great scaled because it uses
mathematical formulas to make sure all the points on the paths maintain their
original relationships. The EPS format is good for drawings, but for photographs
you'll stick primarily with good-quality JPEG files.
