This macro allows comprehensive resampling and color model changes for bitmaps in your document.

It’s the fastest way to convert numerous bitmaps to another color model, and/or change their resolution.

• It has the ability to find bitmaps inside Groups, and also within Powerclips.
• It also features a single Undo.
• 8-bit Alpha Channels are preserved when found in an image.
• A handy Adaptive Unsharp option helps restore detail in downsampled images.
• Images under the new desired resolution can be ignored. For example, this allows images over 300 DPI to be reduced, while leaving existing images under 300 DPI alone.

See it here.