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XnView MP vs Castle Image Viewer: catalog facts
XnView MP	Castle Image Viewer
Freemium Free for private and educational use. A commercial licence is required for business use.	Free Free and open source under the GPL.
Windows, macOS, Linux	Windows, macOS, Linux, Command line
Reads more than five hundred formats including RAW, HEIC and JPEG XL Batch conversion, renaming and adjustment across whole folders	Reads texture formats like KTX and DDS that many viewers cannot Alpha bleeding for textures with transparency
Closed source Commercial use requires a paid licence	Editing is limited to a few specialised functions Interface is aimed at game developers rather than photographers
Downloadable app	Downloadable app
Closed source	Open source
License not stated	License: GPL-2.0-or-later
No account needed	No account needed
Works offline	Works offline
Official website Full listing and sources Checked September 21, 2026	Official website Full listing and sources Checked October 2, 2026

Catalog facts only. Anything “not stated” is unconfirmed. Check full listings for details.