XnConvert

This is a fast, powerful, and free cross-platform batch image converter. It allows you to automate editing for your massive photo collections; you can rotate, convert and compress your different images, photos, and pictures easily and apply over 80 actions (like resize, crop, color adjustments, filter, …). All common picture and graphics formats are supported (JPEG, TIFF, PNG, GIF, WEBP, PSD, JPEG2000, OpenEXR, camera RAW, HEIC, PDF, DNG, CR2).