Adobe Photoshop CS4 - Manual (Page 476)

469 USING PHOTOSHOP CS4
Saving and exporting images
Last updated 1/10/2010
Portable Bit Map format
The Portable Bit Map (PBM) file format, also known as Portable Bitmap Library and Portable Binary Map, supports
monochrome bitmaps (1 bit per pixel). The format can be used for lossless data transfer because many applications
support this format. You can even edit or create such files within a simple text editor.
The Portable Bit Map format serves as the common language of a large family of bitmap conversion filters including
Portable FloatMap (PFM), Portable Graymap (PGM), Portable Pixmap (PPM), and Portable Anymap (PNM). While
the PBM file format stores monochrome bitmaps, PGM additionally stores grayscale bitmaps, and PPM can also store
color bitmaps. PNM is not a different file format in itself, but a PNM file can hold PBM, PGM, or PPN files. PFM is a
floating-point image format that can be used for 32-bits-per-channel HDR files.
Radiance format
Radiance (HDR) is a 32-bits-per-channel file format used for high dynamic range images. This format was originally
developed for the Radiance system, a professional tool for visualizing lighting in virtual environments. The file format
stores the quantity of light per pixel instead of just the colors to be displayed on-screen. The levels of luminosity
accommodated by the Radiance format are far higher than the 256 levels in 8-bits-per-channel image file formats.
Radiance (HDR) files are often used in 3D modeling.
Scitex CT
Scitex Continuous Tone (CT) format is used for high-end image processing on Scitex computers. Contact Creo to
obtain utilities for transferring files saved in Scitex CT format to a Scitex system. Scitex CT format supports CMYK,
RGB, and grayscale images and does not support alpha channels.
CMYK images saved in Scitex CT format often have extremely large file sizes. These files are generated for input using
a Scitex scanner. Images saved in Scitex CT format are printed to film using a Scitex rasterizing unit, which produces
separations using a patented Scitex halftoning system. This system produces very few moiré patterns and is often
demanded in professional color work—for example, ads in magazines.
Targa
The Targa (TGA) format is designed for systems using the Truevision video board and is commonly supported by
MS-DOS color applications. Targa format supports 16-bit RGB images (5 bits x 3 color channels, plus one unused bit),
24-bit RGB images (8 bits x 3 color channels), and 32-bit RGB images (8 bits x 3 color channels plus a single 8-bit alpha
channel). Targa format also supports indexed-color and grayscale images without alpha channels. When saving an
RGB image in this format, you can choose a pixel depth and select RLE encoding to compress the image.
TIFF
Tagged-Image File Format (TIFF, TIF) is used to exchange files between applications and computer platforms. TIFF
is a flexible bitmap image format supported by virtually all paint, image-editing, and page-layout applications. Also,
virtually all desktop scanners can produce TIFF images. TIFF documents have a maximum file size of 4 GB. Photoshop
CS and later supports large documents saved in TIFF format. However, most other applications and older versions of
Photoshop do not support documents with file sizes greater than 2 GB.
TIFF format supports CMYK, RGB, Lab, Indexed Color, and Grayscale images with alpha channels and Bitmap mode
images without alpha channels. Photoshop can save layers in a TIFF file; however, if you open the file in another
application, only the flattened image is visible. Photoshop can also save notes, transparency, and multiresolution
pyramid data in TIFF format.