Adobe Photoshop CS5 for Photographers - Martin Evening [60]
The Cache Level settings affect the speed of the screen redraws. Whenever you are working with a large image, Photoshop uses a pyramid type structure of lower resolution cached versions of the full resolution picture. Each cached image is a quarter scale version of the previous cache level and is temporarily stored in memory to provide speedier screen previews. Basically, if you are viewing a large image on screen in ‘Fit to screen’ display mode, Photoshop uses a cache level that is closest to the fit to screen resolution to provide a screen refresh view of any edit changes you make at this viewing scale. The cached screen previews can therefore provide you with faster screen redraws and larger images can benefit from using a higher cache level, since a higher setting provides faster screen redraws but at the expense of sacrificing the quality of the preview. This is because a lower resolution cache preview is not as accurate as viewing an image at Actual Pixels.
The optimization buttons can help you set the cache levels to an appropriate value. If you mostly work on small images such as Web design layouts, which are small in pixel dimension size but may contain lots of complex layers, you'll gain better performance by clicking the Tall and Thin button to set the Cache Levels to 2. If you mostly work with large images, but not quite so many layers, you can click on the Big and Flat button to set the Cache Levels to 5, although you may wish to override this and set the cache levels even higher than this.
Scratch disk checks
When you launch Photoshop it checks to see how much hard disk space is free for scratch disk usage and if for any reason have less scratch disk space than RAM memory space, the RAM memory will be restricted by the amount of scratch disk space that is available.
The Cache Tile Size can be adjusted according to what is the most appropriate setting for the type of work you do. There used to be an optional Bigger Tiles plug-in that you could install in order to boost Photoshop performance when editing large images. This has now been done away with and the tiling options are instead now incorporated into the Performance preferences. The Cache Tile Size can be set anywhere from 128K–1024K, and tests suggest the optimum settings to choose from are 128K/1024K for the newer Intel processors and 132K/1028K for AMD processors. For image editing work with large photo-sized documents where throughput, i.e. image size, is more of a consideration, it is better to choose a larger Cache Tile Size here.
Move don't copy
To copy selections and layers between documents, use the drag and drop method with the move tool. This saves on memory usage and also preserves the current clipboard contents.
Scratch disks
Photoshop can utilize the free hard disk space that's allocated in the Scratch Disks section as an extension of RAM memory. Photoshop always makes the most efficient use of the real RAM memory and tries to keep as much RAM as possible free for memory-intensive calculations. Low-level data, like the ‘last saved’ version of the image, is stored in the scratch disk memory giving priority to the current version and last undo versions being held in RAM. Normally, Photoshop uses all the available free RAM as buffer memory in which to perform real-time calculations and mirrors the RAM memory contents on the scratch disk. Photoshop does this whenever there is a convenient opportunity to do so. For example, after you open a new image you may notice some disk activity as Photoshop writes from the RAM memory buffer to the scratch disk. Photoshop then continually looks for ways to economize the use of RAM memory, writing to the hard disk in the background whenever there are periods of inactivity. Scratch disk data is also compressed when it is not in use (unless an optional plug-in extension that prevents this has been loaded at startup).
When Photoshop exhausts its reserves of RAM memory, it is forced to use the extra space on the scratch disk as a source of virtual memory and this is