Icon resources
Custom icon data can be supplied for icons of different sizes and color depths, and it can be stored in two basic formats. The software creating the custom icon determines which data it will store when creating icons.
Sizes and color depths (a short history lesson)
Prior to System 7, Macintosh icons were limited to black and white (1-bit) icons in small (16x16 pixels) and large (32x32 pixels) sizes. System 7 introduced support for icons with sixteen colors (4-bit) and 256 colors (8-bit), and custom icons. Custom icon data was stored in resources, one resource for each size and color depth. Mac OS 8.6 added support for icons with millions of colors (32–bit) and transparency, and introduced a new data type, the icon family resource, for storing all sizes of icons in a single icon family. Mac OS X 10.0 introduced support for icon sizes up to 128x128 pixels. Mac OS X 10.6 introduced support for two larger sizes, 256x256 pixels and 512x512 pixels. The more icons included in an icon family, and the larger their sizes, the more space they require on disk. Icon families in Mac OS X is always stored in an icon family resource as part of another file such as an alias file, or alone in a .icns file.
Which icon data do I need?
If you have a lot of files with custom icons and wish to conserve disk space you can have File Buddy remove the sizes you never view. Finder can scale icon date up or down if needed, so intermediate sizes in particular are of limited value.
Why trim a custom icon?
Disk space. Custom icon data increases file size. Larger icons and more sizes in an icon increase the amount of icon data stored in the file. Given the size of modern hard disks, this isn;rsquo;t an issue if you only have a limited number of files with custom icons, but if you're using a smaller drive, such as solid state drive (SSD), you may find it worth the effort to trim custom icon if you are trying to conserve disk space.
Depending on the application which created the icon, custom icon data may contain formats and/or sizes you never see. If this is the case, you can reduce the disk space required to store the icon by removing that unnecessary icon data.
Aliases created by the Finder in Mac OS X are often given a custom icon, and in many cases that can add as much as 70K to the size of an alias file which would otherwise require only a few kilobytes of disk space. These aliases can be good candidates for icon trimming. These files also contain icon data appropriate for displaying a custom icon in the Finder prior to Mac OS 8.6. Most File Buddy 8 users can safely remove this data as well.
Preview resources are resources used by file selection dialogs when selecting picture files. Preview resources contain no custom icon data, and not all picture files have preview data.
Preview data can also be removed by the Trim Custom Icon command to save additional disk space if desired.
Trimming
Custom icon and preview trimming are available in two locations:
- The Trim Custom Icons button in the Select Action dialog. This is that dialog that can be displayed when items are dropped on File Buddy in the Finder. This option will not work for trimming icons in aliases because the Finder resolves all aliases before an application sees them when dropped on the application.
- The command in the List window toolbar's Actions menu. If you wish to trim the custom icons in aliases, this is the only option for doing that.
In either case, select the items and formats to be removed in the dialog displayed by the command.
The current implementation of Trim Custom Icons only operates on files whose custom icon data is stored in the resource fork of the file. It does not work on bundled applications, bundled files, or folders.
