It would be nice if we could simply hand off a Photoshop master document to everybody, but that's not always possible. You're often required to provide a simplified document to exacting specifications based on the final medium. Such a document becomes the opposite of a Photoshop master document. Instead of carrying all possible data for any kind of output, you tune the document perfectly for one specific kind of output. You might constrain the image to a specific color mode, file format, and resolution, and you might be required to flatten layers. Table 15.1 lists some typical output specifications for popular media, but for your own projects you'll want to confirm the exact production specifications of your particular job.
Table 15.1. Sample Document Specifications for Different Media
Typical final specifications
CMYK TIFF or EPS document at 300 dpi
World Wide Web
sRGB document in JPEG, PNG, or GIF format at the required pixel dimensions (resolution doesn't matter)
Digital video (standard definition)
sRGB document at the required pixel dimensions, typically 720 x 480 pixels but depends on video format
Digital video (high definition)
sRGB document at the required pixel dimensions, up to 1920 x 1080 pixels
Table 15.1 represents specifications that mainly apply to programs that don't read Photoshop documents directly. Most Adobe Creative Suite and Adobe Production Studio programs can open or import 8-bit Photoshop documents without modification, saving you the trouble of converting to another format or having to read this section; see "Using Photoshop with Adobe Creative Suite."
Conforming a Photoshop document to media-specific settings can sometimes take you all over Photoshop. Table 15.2 is a handy cheat sheet for where to go in Photoshop to change the most common document specifications that need to be changed for a specific medium.
Table 15.2. How to Make Changes for Media Compatibility
To change this…
Dimensions and resolution
Choose Image > Image Size
Color mode (RGB to CMYK)
Image > Mode > CMYK Color
Color space (convert to a profile)
Edit > Convert to Profile
Image > Mode > 8 Bits/Channel
Layers to a flattened document
Layer > Flatten Image
If you often perform the same sequence of steps to prepare a master document for a specific medium, turn those steps into an action or script; see Chapters 17 and 19.
Bit Depth: How Much Does It Matter?
You might hear about 8-bit and 16-bit images, and claims of higher bit depths are used to help sell hardware and software. Should you be using a higher bit depth for your master document or media-specific document? You can think of bit depth as being analogous to resolution, but instead of describing how many pixels an image has, bit depth describes how many separate levels of tone or color a pixel can store in each color channel (such as the red channel in an RGB image). Although 16-bit images can provide advantages for the capture and editing phase, 8 bits per pixel is still the standard for exchanging completed files for print, Web, and most video media, and most images are still edited in 8-bit color. There's no advantage to converting from 8- to 16-bit color. If you prefer to edit in 16-bit color, keep in mind that you'll probably need to convert your images to 8-bit color if you're handing them off to someone else.
16-bit color gives you additional flexibility in editing by helping prevent visible steps (banding) in tones and colors, but only if the original image was a high-quality capture at 16 bits per channel. (A badly captured 16-bit image is simply 16 bits of garbage.) 16-bit images require much more processing power, RAM, and disk space than 8-bit images, and you gain no color benefits without a calibrated monitor, so you don't want to use 16-bit color without a good reason. If the source image is well captured, and you can make tone or color corrections with just a few adjustments, you may not need to use 16-bit images at all. And if you're just starting out, 8-bit color is the easy choice because it's widely used and supported.
16-bit color is suitable for those who have specific quality requirements and the equipment and skills to support 16-bit editing throughout their workflow. If the use of 16-bit color is something of a niche, then who uses 32-bit color, which Photoshop CS2 supports? There are some high-end uses where the ability to store 32 bits per channel of tone and color actually helps, such as astronomy, Hollywood and game industry special effects, and high-end landscape and architectural photography.