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This chapter is from the book

Mastering the Adobe Creative Suite

Formats and Platforms

What makes .tif or .psd files different in Macintosh and Windows?

Actually, nothing. A file extension indicates a particular file type. File types are almost always standardized so that they work equally well on both Windows and Macintosh computers (assuming that the appropriate program is available). However, the file must be on a disk or drive that can be read by the computer. Macintosh computers can read and write Windows-formatted disks, but Windows computers can't read Mac-formatted disks without a utility.

Remember, too, that file formats can change with versions of the software. Just as a PSD file created by Photoshop can have features that cannot be used in Photoshop 4, so, too, do the most recent DOC files from Microsoft Word have features unavailable in Word 4.2.

Hard and Variable Transparency

I want a soft drop shadow around my image, but Export Transparent Image always seems to leave a white halo below the shadow.

The transparency generated for EPS and GIF files is hard-edged transparency, in which a pixel is either completely transparent or completely opaque. Your drop shadow relies on variable transparency, in which pixels can be partially transparent.

Save for Web can now generate GIFs with dithered transparency, interspersing opaque pixels and transparent pixels. Print applications are a good bit trickier. InDesign 2.0 supports variable transparency, but other page layout programs do not. There are various techniques for simulating such effects as drop shadows, but generally it's easier to replicate the page's background in Photoshop.

Lossy Compression

I want to get my files really small for the Web, but it takes a long time. I save an image at one compression level and open it up to look at it. Then I have to go back and try a different compression level to get what I want. Isn't there a way to preview an image being saved as a JPEG?

Use the menu command File, Save for Web. This feature allows you to compare up to four versions of the same image, all at the same time. You pick the versions that best meet your needs for quality and file size and then click OK.

RGB for the Web

I created JPEG files of a lot of the images my company used in its latest brochure so that I could post them on the Web, but they don't show up. I exported them as JPEGs, so what's the problem?

For a brochure, eh? I'll bet those images were CMYK. Although that color mode is perfectly acceptable for JPEG, it's not acceptable on the Web. Your images need to be converted to RGB before they can be seen by a Web browser. Throw away the CMYK JPEGs and go back to the originals. Use Save for Web rather than Export, and the color mode will automatically be converted for you.

What's that? Why does JPEG accept CMYK if you can't see it on the Web? Well, JPEG does more than just Web graphics. It's also one of the major file formats used to compress images for storage or archiving—and many of those images are CMYK.

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