Teach.Yourself.Adobe.Photoshop.CS2.in.10024.Hours [Electronic resources] نسخه متنی

Saving Your Work

Theres one very important thing to know about saving your work: Do it often! Computers are prone to unexpected shutdowns and errors. Saving takes only a couple of seconds, and it can make the difference between having to do your work all over again or just reopening it if the computer shuts down.

The first time you save a picture, youll see the Save As dialog box, as shown in Figure 2.5. Give the file a name and select an appropriate format to save it in from the pop-up menu. After this, click Save or just press Command+S (Mac) or Control+S (Windows) to save the file.

Cross-Platform Concept

For Macintosh users only: If you have to work cross-platform, that is, on both a Macintosh and PC, you should always choose to include file extensions with your files. This option is found in the Preferences dialog box. Also, always check Use Lowercase to be sure that your file is Windows and UNIX compatible.Hour 24.

Reducing File Size

As you start to work with different Photoshop files, youll notice that your hard drive is starting to fill up. Photoshop files can become large very quickly. You can make your files smaller in several ways:

Reduce the resolution or the physical size of the image

Reduce the number of colors in the image palette

Use a format that compresses the file

Use a compression utility after the file is saved

Merge layers in native Photoshop files

Delete any alpha channels that are no longer needed

Reducing the resolution is not a good idea if youre going to print the image. If the picture is going to be viewed only on your computer screen or on the Web, reduce the resolution to 72 dpi. Be aware, though, that increasing the resolution again, if you change your mind, reduces image quality. You can change the resolution in the ImageImage size dialog box. Dont make it less than 72 dpi.

Reducing the number of colors means reducing the bit depth. This can make your colors look blotchy onscreen and in print. If you are working in grayscale (no color in the picture), reduce the bit depth to 8 bits by choosing Grayscale in the Image Mode submenu. This gives you 256 shades of gray, which is more than a printer can print.

Using a compressed format means choosing a file format, such as TIFF with LZW compression, that automatically shrinks the file down as small as possible when it saves. It does this by a means called lossless compression, so theres no image degradation or blotchy color. LZW compression (named for its inventors, Lempel, Ziv, and Welch) is also used by GIF and PDF formats.

There are also formats, such as JPEG, that use lossy compression. Lossy means, as you might guess from the name, that some of the data that makes up the image is lost in the compression process. Instead of 20 shades of blue in the sky in a TIFF file, the same image in a JPEG file might have only 5 shades of blue. And, yes, you can see the difference. Unfortunately, compression is necessary when you are placing images on the Web, in a multimedia presentation, or in another situation where upload time or storage space is limited. JPEG saves files in the least possible amount of disk space. One point to remember is that if you save a JPEG image a second time as a JPEG, it is compressed again and loses more information. If you work on a JPEG file a lot, you can end up with an unreadable picture. If youre going to work on a picture, save it as a Photoshop file. Dont make it a JPEG until youre done with it and ready to post it on your Web page. If you have to change the image, trash the JPEG file and go back to the Photoshop version.

When you have files you want to save for future reference, you can save them in the normal way as Photoshop documents (with a .psd filename extension) or in whatever format you prefer to work in, and then compress the files with a utility such as StuffIt or PKZip or WinZip. All these file compression utilities use lossless compression algorithms and shrink your image files by anywhere from 20% to 50%. That said, compressing JPEG or GIF files is relatively useless because theyre already compressed. You wont gain more than a few percent of additional compression.

Figure 2.6 shows a typical digital photograph that I saved in a number of different file types. (The original is about 5 inches wide, and saved at 200 dpi.) Table 2.1 shows the more common file types and the sizes of the files that this picture required. The version shown is a PSD, the native Photoshop format.

Table 2.1. File Format/File Size Comparisons for Figure 2.6

Photoshop native

1.97MB

BMP

1.97MB

EPS

2.82MB

GIF

536KB

JPEG (high quality)

272KB

JPEG (low quality)

192KB

PDF (medium quality)

188KB

PNG (interlaced)

1.3MB

TIFF (LZW compression)

1.4MB

Choosing a Format

With so many possible formats, how can you decide which one to use? Its really not so difficult. As long as you are working on an image, keep saving it as a Photoshop document (.psd). This makes sense, especially after you learn to work in layers, because Photoshops native format can save the layers, whereas most other formats require that you merge the layers into one. After you have flattened the layers, you cant split them apart again. So, bottom line, as long as you think youll want to go back to a picture and modify it, save a copy as a Photoshop document.

When you finish working on the picture and are ready to place it into another document for printing, save a copy as an EPS file if its going to a PostScript-compatible printer. If you arent sure how it will be printed, save it as a TIFF because TIFF is compatible with most printers and page-layout programs. If youre going to place your picture on a Web page, choose GIF if the picture is line art, has large areas of solid color, or uses a limited color palette. Choose JPEG or PNG if the picture is a photograph or continuous tone art (lots of colors). If you want to import the picture into some other graphics program for additional work, choose Photoshop format (PSD) if the other program supports it, and TIFF if the other program doesnt recognize Photoshop files.