Speeding Photoshop

No-one wants to wait for struggling applications when you're trying to be creative. Optimize your image editing with Digit's guide to getting the quickest possible performance from Adobe Photoshop.

Most people would prefer not to see Mac OS X’s spinning beach ball when working in Photoshop. Although eliminating it is not always possible, you can go some way toward doing that by managing your resources wisely. To that end, it’s worth spending a few minutes fine-tuning Photoshop to squeeze the maximum performance out of it.

Adjusting cache levels

When you view an image in the document window at anything less than 100 per cent magnification, Photoshop can use low-resolution cached versions of the 100 per cent view for speedier redraws. This can be helpful if you constantly work on large images and need to zoom out frequently. However, it will take longer to open files while Photoshop creates the low-resolution previews.

You can specify the number of cache levels in the Preferences: Memory & Image Cache screen (press Control/Command+K to open the Preferences dialog box). The higher the number of cache levels, the more resources Photoshop needs to consume. If you have limited RAM or scratch-disk space, you may wish to set the number of levels to 1 or 2; the default is 4 levels. You can go as high as 8 levels, which will give you cached views at 66.67, 50, 33.33, 25, 16.67, 12.5, 8.33, and 6.25 per cent.

Although the cached views can help with speedier redraws, you’ll do well to remember that any reading based on a cached view will be misleading. For example, when you sample a colour or use a cached view to judge the effect of a filter, what you’re looking at will not be based on actual pixels. For critical readings, always view the image at 100 per cent magnification.

Reducing history states

The History feature has become one of the most widely used in Photoshop. Its major downside is that it’s another resource hog.

But you can change several options to conserve and stretch your resources. The first is the number of History states that Photoshop saves in RAM or on your scratch disk. The higher the number, the more resources are eaten up. However, the higher the number, the more undos are available to you should you need to step back to a previous state. You need to strike a good balance between a fallback position and the ability to cruise faster.

By default, Photoshop saves 20 History states. You can change this number at any time via the Preferences: General screen’s History States setting. If you find that you rarely go back beyond, say, ten history states, then reducing the number will allow the saved resources to be used elsewhere. If you find yourself constantly trying to find states that have disappeared from the History palette, then increase the default number and just put up with slower performance, which may not be noticeable if you have small files or if you have large reserves of RAM.

Reducing palette thumbnail size

The palettes also have options that can affect performance. For example, the Layers, Channels, and Paths palettes all store thumbnails by default, and these thumbnails are continually updated as you work on an image. However, to draw and update the thumbnails, Photoshop uses resources that may be gainfully employed elsewhere. If your resources are painfully low, you may want to select None or the smallest thumbnail size. To customize the palette previews, select Palette Options from the palette’s menu and then choose an option that suits your needs.

Do you really need that snapshot?

You can set other options that affect performance by selecting History Options from the History palette menu.

The first two options in the History Options dialog box, Automatically Create First Snapshot and Automatically Create New Snapshot When Saving, are the ones that consume extra resources.

The first option is actually quite handy, even if it does consume extra resources. It can get you out of a tight spot if you accidentally flatten a multilayered file or press Control/Command+S but don’t discover your mistake until well into the editing session, by which time the earlier states will have been overwritten, including the first state. When you click on the snapshot, the document will revert back to the state it was in when it was first viewed in Photoshop, which may not be the same as the version on disk if you changed its colour profile in any way when you opened it.

The second option (Automatically Create New Snapshot When Saving) is one that you can probably live without -- you’ll have to decide whether to take advantage of it. Just remember that it will consume extra resources if enabled.

Assigning RAM

All the software on your computer, from the operating system to applications to widgets, relies heavily on RAM for speed and efficiency. Photoshop can guzzle RAM the way a Merc guzzles petrol. So you need to give it as much RAM as you can possibly afford. The operating system also needs a plentiful supply of RAM, so it’s a bad idea to starve it while indulging Photoshop.

Photoshop gets its share of RAM from the figure allocated to it in Preferences. When it has used up its allocation, it pages out the data to the hard disk (allocated to it as the scratch disk in Preferences), and the result is that it runs more slowly. Knowing this, you may be tempted to max out the RAM allocation at 100 per cent in order to make it run faster. This not a good idea -- Allocating too much memory to Photoshop may slow down performance by forcing the operating system and Photoshop to swap pages in and out of memory. So what amount of available RAM should you allocate? It depends.

Photoshop can use a maximum of only 4GB of RAM. This limitation is imposed by hardware, operating systems, and some other things that only geeks and engineers with degrees in astrophysics understand fully.

Suffice to say, if you have 4GB of RAM, or more, installed, you can safely increase the RAM allocation to 70 per cent. Doing so will ensure that Photoshop uses as much RAM as it possibly can, up to the 3.7GB limit (or thereabouts, because the OS will reserve some of the 4GB for itself). If you do not have more than 4GB of RAM installed, you should reduce the allocation to about 50 or 60 per cent, especially if you are experiencing slow performance in Photoshop, which includes Camera Raw. To allocate RAM, go to Preferences: Memory & Image Cache and specify a per centage in the Memory Usage section of the dialogue box. You will need to restart Photoshop before the revised allocation takes effect.

Assigning scratch disks

Photoshop uses a temporary file for storing data and performing computations when there is insufficient RAM. It places this temporary file, or scratch disk, on your hard disk, or it can spread the file across several hard disks. When you exit Photoshop, this temporary file is deleted, and a fresh one is created the next time you launch Photoshop.

By default, Photoshop uses your startup hard drive as the location for the scratch disk. This is something to be avoided because it can hinder performance if your OS also uses that drive for its virtual memory needs. Because OS X uses the start-up drive to place its paging file, you are almost guaranteed conflict on a Mac. To overcome this potential conflict of interests, you can tell Photoshop which hard disk to place its scratch disk on -- provided, of course, that you have more than one hard disk installed in your computer. If you have just one disk but it’s partitioned, selecting a partition different from the one containing the OS virtual memory files won’t speed up performance. In fact, performing some operations may even take longer because the read-write heads will have to travel further.

You can assign scratch disk(s) in the Preferences: Plug-Ins & Scratch Disks screen. It’s possible to assign up to four hard disks, or partitions, and Photoshop will see them as one large storage space for the temporary file. Photoshop supports up to 64EB (an exabyte [EB] is equal to 1 billion gigabytes) of scratch-disk space -- more than sufficient for most needs.

Regardless of the number of hard disks you assign, make sure the minimum size is three to five times the RAM allocated to Photoshop. Furthermore, the hard drive should be fast, and if it’s partitioned, the first partition should be assigned. Do not assign removable media, such as a Zip drive, or a network drive as a scratch disk. If you assign dedicated partitions that do not store any other files, defragging should not be required.

The more space you can spare, the lower the likelihood that you will encounter the dreaded “Scratch Disk Is Full” error message at a crucial moment.

This article is an excerpt from Hacking Photoshop CS 2, by Shangara Singh (2005; reprinted by permission of Wiley Publishing).

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