Starting with AGG version 0.2.3, AGG includes a Batch Resizer tool, which can be handy if you want just to resize (and skip
unneeded gallery creation) of a large bunch of images. It is a bit more powerful, too, since you can resize images
recursively in a whole directory tree.
Example of the resizing dialog
Resize files in: Choose the source directory
Recursive: Include also files in all subdirectories.
Keep Directory structure: Only with recursive option: preserve the directory structure in the output folder. If it is not ticked, the hierarchy is "flattened" in the output directory - all images are put in a single directory. This can be potentially dangerous, if you have lots of identically named files in different directories, since their output filenames will coincide (but don't worry, AGG will warn you if this is the case).
Output directory: This is where to put resized images. It can be the same as the input, in which case images are destructively resized and originals are lost forever. Think twice before applying this operation to a large directory three.
Include: Select which type of image files you want to process
Convert to: Select the output image format.
Resize to: The destination resize length on the larger image side. Same restrictions as in galleries apply: AGG will never upscale an image; small images will simply be untouched (but the Load/Save cycle is present, which in the case of JPEG can ruin the quality - keep that in mind).
JPEG Quality: The quality of the resulting JPEGs. Useful values: 5-95.
Resize using: Select which resizing algorithms to use when shrinking the images. See comparison between them here.
Preserve Exif metadata: Un-ticking this will strip Exif metadata from JPEG files that have it. It is usually worth a few kilobytes per image.
Rotate images according to Exif: This will physically rotate images, that have set the image orientation tag in the Exif (most modern cameras with orientation sensors have it set). Useful if you plan to strip the Exif metadata or if you intend to view the resulting images with a viewer, that doesn't automatically rotate images according to Exif.