Adobe Photoshop CS5 for Photographers - Martin Evening [34]
Figure 1.89 The ‘non-linear history’ option allows you to branch off in different directions and simultaneously maintain a record of each history path up to the maximum number of history states that can be allowed. Shown here are three history states selected from the History panel: the initial opened image state (A), another with a Curves layer adjustment (B) and thirdly, an alternative version where I added a Black and White layer adjustment layer followed by a Curves adjustment layer to add a sepia tone color effect (C).
Non-linear history requires a little more thinking on your part in order to monitor and recall image states, but ultimately makes for a more efficient use of the available scratch disk space. Overall, I find it useful to have non-linear history switched on all the time, regardless of whether I need to push this feature to its limits or not.
Non-linear history in use
On pages 434–435 in Chapter 8 you can see a practical example of how the History feature might be used in a typical Photoshop retouching session.
When files won't open
You can open an image file in Photoshop in a number of ways. You can use the Bridge program or Mini Bridge panel (which are described on pages 76–81), or you can simply double-click a file to open it. As long as the file you are about to open is in a file format that Photoshop recognizes, it will open in Photoshop and, if the program is not running at the time, this action should also launch Photoshop.
Corrupt files
There are various reasons why a file may have become corrupted and refuses to open. This will often happen to images that have been sent as attachments and is most likely due to a break during transmission somewhere, resulting in missing data.
Every document file contains a header section, which among other things tells the computer which application should be used to open it. For example, Microsoft Word documents will (naturally enough) default to opening in Microsoft Word. Photoshop can recognize nearly all types of image documents regardless of the application they may have originated from, but sometimes you will see an image file with an icon for another specific program, like Macintosh Preview, or Internet Explorer. If you double-click these particular files, they will open in their respective programs. To get around this, you can follow the instructions described in Figure 1.90. Alternatively, you can use the File Open command from within Photoshop, or you can drag a selected file (or files) to the Photoshop program icon, or a shortcut/alias of the program icon (Figure 1.91). In each of these cases this allows you to override the computer operating system that normally reads the file header to determine which program the file should be opened in. If you use Bridge as the main interface for opening image files in Photoshop, then you might also want to open the File Type Association preferences (that are described in Chapter 11) to check that the file format for the files you are opening are all set to open in Photoshop by default.
Figure 1.90 The header information in some files may contain information that tells the operating system to open the image in a program other than Photoshop. On a Macintosh go to the File menu and choose File Get Info and under the ‘Open with’ item, change the default application to Photoshop. On a PC you can do the same thing via the File Registry.
Figure 1.91 When files won't open up directly in Photoshop the way you expect them to, then it may be because the header is telling the computer to open them up in some other program instead. To force open an image