Sheets This OS X widget automates the process for creating sprite sheets using image sequences. ImageMagick allows animations to be created in strips, sheets or with custom settings for scale, tiling, and other settings. You can also create file sheets (also known by contact sheets), with the file name and original size clearly labeled underneath each thumbnail. When necessary, large collections can be paginated automatically.
Images can be a collection. Select multiple files in Finder and click-drag while opening Dashboard. Or, a single image from a numerical sequence. Sheets will automatically collect the rest of the images for you sequence. Images can be sorted lexicographically. Files that contain multiple files and different file names can be grouped together. For best results, full serial numbers are required (0000 to 0100 will sort correctly, while 100 through 100 won't).
The preferences side of the widget lets you choose the scaling algorithm to scale images to fit into specific dimensions. New are the alpha output options: transparent (premultiplied), flattened/removed, extracted (alpha only), multiple files. This produces transparent, RGB and A files that can be used in other tools that require straight RGB input. ImageMagick, for example, doesn't support straight RGB in TIF format so multiple files are the only way you can keep all RGB data.
The output filename is taken directly from the first image of the series. It replaces the frame number by a title that you have set in your preferences. For example, a group of images starting with animation_ver1_0000.png by default will result in animation_ver1_spriteSheet.png.
ImageMagick is required to run this widget. Please visit imagemagick.org for more information. My experience with MacPort (macports.org), while it can take a long time to install, it requires far less user input. You just need to set it up and then let it run for a while as it installs everything automatically.