Photoshop supports a variety of image file types. Most people tend to work with one or two types and leave the others alone. However, having a basic understanding of all file types helps you make better choices when you have to work with them. The following sections describe some image file types and advantages/disadvantages of them.
Photoshop natively uses its own Photoshop PSD file format. This file format contains all the information relevant to working with the image within Photoshop. For example, all the layer data you have created when working with the image is stored in the PSD file. Use the PSD file format when working with the image in Photoshop. The work done in Photoshop to create adjustment layers and other changes usually represents lots of work. The PSD file is the only format that stores all your work so you can fine-tune your adjustments later. The file format maintains the full image data, so you need not worry about saving it multiple times. PSD files can store image data in 8 bits per channel, 16 bits per channel, and 32 bits per channel. One disadvantage of the Photoshop file format is that it takes up a large amount of disk space compared with some of the other file formats.
TIFF (Tagged Image File Format) is the next best format to PSD when saving your files. TIFF images can be stored in 8 bits per channel, 16 bits per channel, and 32 bits per channel. Advantages of the TIFF file formats are that it stores the layers that you create in Photoshop and can store transparency in the form of an alpha channel .TIFF images are also fairly large comparatively, so you may not want to use this file format for most images you will be working with. Another disadvantage is that TIFF images are typically not supported in Web browsers, so you can’t add them to Web pages.
The JPEG file format has become by far the most commonly used. The JPEG format provides very good image quality supporting 16.8 million colors, combined with one of the best compression Algorithms. This makes JPEG images the best quality for the file size that you can get. Consequently, most cameras use the JPEG image format by default. JPEG images are read by almost every computer program and are easily incorporated into Web pages. They also take much less disk space than PSD and TIFF files because they are compressed.
JPEG 2000 (*.JP2;*.JPX)
The JPEG 2000 file format uses a different encoding and compression system that makes the compression lossless. In addition, the JPEG 2000 file format supports 16-bit color for a greater range of colors, grayscale images, and 8-bit transparency. Although JPEG 2000 files provide a number of advancements over JPEG, they are not as widely supported and so they are still not used as often. Adobe provides a plug-in for Photoshop that will allow you to read and save files in the JPEG 2000 format.
JPEG images use a lossy compression algorithm, which means the more you change and save them, the worse the quality of the image becomes. You should convert the JPEG images to either PSD or TIFF to edit them and then back to JPEG when you are finished making the changes.
CompuServ GIF (*.GIF)
The GIF (Graphics Interchange Format) has been the main graphic file used in developing Web pages since the inception of the World Wide Web. The GIF uses an 8-bit palette that is limited to 256 colors. The 8-bit palette makes the GIF images very small and easily transferred across the Internet. This makes the GIF file perfect for creating images such as buttons, links, icons, and so on that are displayed on Web pages.
A cool advantage of the GIF supports animation effects within the image. This allows you to create animated controls and icons for Web pages. The GIF file format is lossless, so there is no data loss when saving files.
The PNG (Portable Network Graphics) was designed to replace the GIF for use on the Internet. The PNG file format has an advantage over GIF in that it supports 16.7 million colors as opposed to GIF supporting 256. However, there are still some drawbacks to the PNG . Some Web browsers do not support it, and while others support it, they do not handle things such as transparency and gamma correctly. As browsers become more adept at handling the PNG format, it definitely will replace the GIF file format, but for now you should consider working with GIF for Web images unless you need the additional colors available in PNG.
Bmp (*.BMP; *.RLE; *.DIB)
The BMP was developed for graphics in the Windows operating system. It is a simple format that is widely accepted by Windows applications. BMP files are not compressed, which makes them large. Another disadvantage is that there is not as much support outside ofWindows—on Macs or Linux operating systems, for example.
RAW (*.RAW; *.CR; *.CR2; *.DNG; and several others)
The RAW image format was designed to capture the basic information collected by the CMOS sensors in digital cameras. Collecting the information directly without converting it to another file format makes the cameras work faster and results in less data loss. One downside to the RAW file formats is that they have little support outside of image editors such as Photoshop. Another downside is that it is not one single format. In addition to the original. RAW file format, other vendors have added their own file formats. Canon has .CR and .CR2. Adobe has .DNG (Digital Negative), which is designed to try to standardize on a single format. So far, the DNG format seems to be getting the best attention and support by hardware and software manufacturers.
The Open file dialog box in Photoshop provides options for Camera Raw and Photoshop RAW. Photoshop RAW are images that are saved in the RAW file format from Photoshop. The Camera Raw options are for files that are saved in a RAW file format by the camera. There are many different file extensions for the Camera Raw option because most camera venders have their own proprietary.
The biggest advantage to using the RAW file is that you can work with the image as close as possible to the state that existed when the photo was taken. Photoshop has designed as special tool, Adobe Camera Raw, specifically for editing photos in the RAW state because the results tend to be much better than in other.
If you are taking photographs that you really want to look good, you should set your camera to the RAW setting and use Adobe’s Camera Raw tools to adjust them. After they are adjusted, you can save them in another format, but if you may want to adjust them again, keep the Camera Raw files around.
Portable bitmap (*.PBM;*.PGM;*.PPM;*.PNM;*.PFM;*.PAM)
The PBM (Portable Bitmap), PGM (Portable Graymap), and PPM (Portable Pixmap) are basic file standards. They are so basic that they serve as one of the best common denominators for transferring files between different platforms, going from Windows to Linux, Using these formats you can overcome those problems more easily. Another advantage of the PBM file format is that it is one of the few formats that can store image data in 8 bit/channel, 16 bit/channel, and 32 bit/channel formats. This is another major advantage when trying to make an image portable from one system to another.
Wireless bitmap (*.WBM;*.WBMPI)
The WBM is designed for images used on wireless devices. Wireless devices are limited in the size and number of colors an image can contain. Using the Wireless bitmap format allows you to create images that can be displayed on most portable devices.
Encapsulated PostScript (*.EPS; *.AI3-*.AI8; *.PS; *.EPSP; *.EPSF)
The EPS (Encapsulated PostScript) file format was developed by Adobe as a means to store images in a format the PostScript printers can understand. That way, the file could be copied directly to the printer without the need to interact with the applications. Later, Adobe realized that this was an excellent means to transfer documents between different programs. Because all Adobe programs understand how to generate and read the EPS files, it was easy for one application to read an EPS file that was generated by another program.
The greatest strength of the EPS system is that it can contain both raster and vector images. This gives you the ability to generate a vector image in another program, in Adobe Illustrator, for example, and then import it into Photoshop. The vector image can then be used by Photoshop as a vector path, for instance.
A major advantage of the EPS is that its files are readable by almost every desktop layout program in use. One disadvantage is that it is not truly a graphic format. The EPS format is definitely not the best format in which to store photos for later editing. Another disadvantage is that the EPS format results in a very large file because the storage format is not efficient.
Photoshop PDF (*.PDF;*.PDP)
The PDF file format was developed by Adobe to be a standard format for files that contained both vector and raster images. It has been widely accepted as a standard file format across all operating systems. PDF files can be read by many applications. When Photoshop opens a PDF file, it allows you to import the pages and images separately. The biggest advantage to the PDF file format is how widely it has been adopted. It is the de facto standard in publishing documents on the Internet, so it can be read everywhere. You will not use the PDF file format much in Photoshop, but it’s great when you need it.
The PCX (Personal Computer eXchange) format was developed for use with the PC Paintbrush utility for DOS. If you don’t know what DOS is, don’t worry; it’s best forgotten. The PCX format was widely used several years ago, but it has lost pace and been replaced with the GIF, JPEG, and PNG file formats.
You probably don’t need to use the PCX file format unless you are using an image that was created several years ago. Keep in mind that PCX files originally had a maximum of 256 colors, so don’t expect PCX files to contain much detail.
PICT files are sort of the Apple version of PCX files. The PICT file format was original developed for use with the QuickDraw utility. The format was one of the few at the time that allowed a file to contain both vector and raster images. However, that functionality has been replaced by the EPS and PDF file formats.
The Pixar file format is a format developed in-house by the Pixar animation company. The requirements of digital animation put such as huge strain on the available applications that they had to create a custom system including their own file format. Photoshop allows you to read images that were created using Pixar’s system and to write your images out to the Pixar file format. It’s probably not useful to most people, but handy when it is necessary.