Photoshop and Photoshop Elements 2 included new Layer capabilities in TIFF files. If
your image contains layers, the following options will be available in the TIFF
Options dialog box:
■ Layer Compression: RLE. Run-Length Encoding. A lossless compression
method. This format, like ZIP compression, is most effective on large areas of
a single color.
■ Layer Compression: ZIP. A lossless compression format similar to LZW.
Use this compression format for layers that contain large areas of a single
color.
■ Discard Layers and Save a Copy. Flattens the layers in the image and
then saves the file as one layer. Annotations remain separate, however.Photoshop and Elements are capable of opening layer-embedded TIFF files, but other
programs might not. In addition, older versions of Photoshop prior to Version 7 can-
not open multilayered TIFF files.94 ABSOLUTE BEGINNER’S GUIDE TODIGITAL PHOTOGRAPHY
RUN-LENGTH ENCODING EXPLAINED
Run Length Encoding (RLE) is a simple compression format that searches for strings of data
(called a run) and encodes the string in two bytes. The first byte (the run count) represents
the number of characters in the run. An encoded run can contain from 1 to 128 or 256
characters. The amount is usually the number minus 1 (0–127 or 255). The second byte
(the run value) is the value of the character in the run, which is in the range of 0 to 255.
For example, assume a string of 20 Xs appears in a document. This would normally require
20 bytes to store:
XXXXXXXXXXXXXXXXXXXX
After run-length encoding the file, the string would be represented by two bytes:
20X
The first byte is 20, which represents the number of Xs it found in the file. The second byte
represents the actual character that appeared in the run.One confusing setting in the TIFF Options dialog box is Byte Order. In the 1990s, the
Mac and Windows platforms were compatible in disk formats, but software still had
to know how and on which platform TIFF files were saved. TIFF files saved on the
Mac used the Mac byte order (obviously). If you opened a TIFF file saved on the Mac
or PC, you had to tell Photoshop where or how the file was saved (IBM PC or Mac).