Adobe PHOTOSHOP ELEMENTS Manual page 260

CHAPTER 12
252
Saving Images
PNG format
Developed as a patent-free alternative to GIF,
Portable Network Graphics (PNG) format is used
for lossless compression and for display of images
on the World Wide Web. Unlike GIF, PNG
supports 24-bit images and produces background
transparency without jagged edges; however, some
Web browsers do not support PNG images. PNG
preserves transparency in grayscale and RGB
images. For information on when to use PNG
format to optimize images, see "Choosing a file
format for optimization" on page 227.
To save a file in PNG format:
1 Choose File > Save As, and choose PNG from
the format list.
2 Specify a filename and location, select saving
options (as described in "Saving images" on
page 246), and click Save.
3 Select an Interlace option, and click OK:
None to create an image that displays in a Web
•
browser only after downloading is complete.
Interlaced to create an image that displays
•
low-resolution versions in a browser while the
full image file is downloading. Interlacing can
make downloading time seem shorter and assures
viewers that downloading is in progress. However,
interlacing also increases file size.
Raw format
Raw format is a flexible file format for transferring
images between applications and computer
platforms. Raw format consists of a stream of bytes
describing the color information in the image.
Each pixel is described in binary format, with 0
representing black and 255 white. You can specify
the file extension (Windows), file type (Mac OS),
file creator (Mac OS), and header information.
In Mac OS, the file type is generally a four-
character ID that identifies the file—for example,
TEXT identifies the file as an ASCII text file. The
file creator is also generally a four-character ID.
Most Mac OS applications have a unique file
creator ID that is registered with the Apple
Computer Developer Services group.
You can save the image in an interleaved or nonin-
terleaved format. If you choose interleaved, the
color values (red, green, and blue, for example) are
stored sequentially. Your choice depends on
requirements of the application that will open
the file.
The header parameter specifies how many bytes of
information appear in the file before actual image
information begins. This value determines the
number of zeros inserted at the beginning of the
file as placeholders. By default, there is no header
(header size = 0). You can save the file without a
header and then use a file-editing program, such as
HEdit (Windows) or Norton Utilities
to replace the zeros with header information.
Targa format
TGA (Targa ) format is designed for systems using
®
the Truevision video board and is commonly
®
supported by MS-DOS color applications. When
saving an RGB image in this format, you can
choose a pixel depth of 16, 24, or 32 bits per pixel.
(Mac OS),
®