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nomacs vs Castle Image Viewer: catalog facts
nomacs	Castle Image Viewer
Free Free and open source under the GPL 3.0.	Free Free and open source under the GPL.
Windows, macOS, Linux	Windows, macOS, Linux, Command line
Opens RAW camera files and Photoshop PSD documents Synchronises pan and zoom between two windows or two machines	Reads texture formats like KTX and DDS that many viewers cannot Alpha bleeding for textures with transparency
Not an editor; adjustments are minimal The interface exposes a lot of panels at once	Editing is limited to a few specialised functions Interface is aimed at game developers rather than photographers
Downloadable app	Downloadable app
Open source	Open source
License: GPL-3.0	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

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