Using the Save as a Copy Feature
The Save as a Copy checkbox in the Save As dialog box is intended to keep you from losing data, but it's a common source of confusion. And sometimes the Save as a Copy comes on all by itself, which adds to the confusion. The key to avoiding confusion is to understand its reason for being.
The Save as a Copy checkbox is there because of the conflicting requirements of master and media-specific documents that I've been talking about. For example, suppose you're preparing an image that needs to be delivered as a JPEG document. While building the document, you save the image in Photoshop format so that you can take full advantage of features like layers, vector type and shapes, and alpha channels. When it's time to hand off the final JPEG, you choose File > Save As and choose JPEG from the Format pop-up menu (Figure 15.1). When you do this, all of the Save option checkboxes become dimmed, and the Save as a Copy checkbox becomes dimmed and enabled. The reason Photoshop does this is to prevent you from replacing the current, full-featured Photoshop document with a JPEG document that can't store all of the Photoshop features you used. In the past, it was too easy to save over your full-featured document with a version that was no more than a flattened document containing only pixels, removing the flexibility of the master document. Whenever you choose a Save As format that can't store all of the features listed in the Save options of the Save As dialog box, Photoshop requires that you save as a copy.
Figure 15.1. In the Save As dialog box, saving a layered, annotated Photoshop document in JPEG format causes Save As a Copy to become enabled and dimmed.
Save as a Copy also becomes enabled if you save in Photoshop or TIFF format but disable any of the Save checkboxes, because once again, you're about to create a document with fewer editing capabilities than your master document.
An important effect of the Save as a Copy feature is that the document you save is not the document that remains open. If you want to work on a document that was saved using Save as a Copy, you must open it separately. The document that's open after you Save as a Copy is the master document you originally opened, and any changes you make to it don't appear in the Save as a Copy version. That's because the Save as a Copy version is like a spinoff of the master document, which makes perfect sense if you were using Save As to create a simplified, media-specific version of the master document.
Playing Nice with Other Programs
Buried in the File Handling panel of the Preferences dialog box is a setting called Maximize PSD and PSB Compatibility (Figure 15.2). Not everyone knows what it's actually for, and a lot of people turn it off after realizing that it makes Photoshop documents take up more disk space. Many believe that it's there so that older versions of Photoshop can read the document, but there's more to it than that.
Figure 15.2. The Maximize PSD and PSB Compatibility checkbox makes it possible for other applications to read feature-rich Photoshop documents, such as layered documents.
Many other programs claim to be able to read Photoshop files, but not all of them understand all of the possible kinds of Photoshop documents. Some programs can only read Photoshop files that are flattened. Others can't read Photoshop documents in 16-bit color, that are layered, or that use the Lab color mode. The Maximize PSD and PSB Compatibility option exists to get around this problem. It embeds a composite (flattened) version of the Photoshop document along with the usual Photoshop layers and other non-pixel datathat's why the document gets bigger. When a program opens or imports a Photoshop document that includes features it doesn't recognize, the program can fall back to the friendly composite version embedded in the document.
If you rarely view Photoshop documents with other programs, you might choose to disable Maximize PSD and PSB Compatibility and save some disk space. However, the more you handle Photoshop documents with other programs, especially non-Adobe programs, the more you want to enable that option. Remember that non-Adobe programs that handle Photoshop documents directly can include graphics-viewing utilities that come with your computer such as Apple Preview, page-layout software, video-production software, and digital-asset managers. Disabling Maximize PSD and PSB Compatibility may limit your ability to preview Photoshop documents in some Adobe programs. I keep it on because large hard disks are affordable.