Adobe photoshop elements User Manual

CHAPTER 12

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.

Choose File > Save As, and choose PNG from 

the format list. 

Specify a filename and location, select saving 

options (as described in “Saving images” on 
page 246), and click Save.

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 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

®

 (Mac OS), 

to replace the zeros with header information.

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.