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Castle Image Viewer vs nomacs: catalog facts
Castle Image Viewer	nomacs
Free Free and open source under the GPL.	Free Free and open source under the GPL 3.0.
Windows, macOS, Linux, Command line	Windows, macOS, Linux
Reads texture formats like KTX and DDS that many viewers cannot Alpha bleeding for textures with transparency	Opens RAW camera files and Photoshop PSD documents Synchronises pan and zoom between two windows or two machines
Editing is limited to a few specialised functions Interface is aimed at game developers rather than photographers	Not an editor; adjustments are minimal The interface exposes a lot of panels at once
Downloadable app	Downloadable app
Open source	Open source
License: GPL-2.0-or-later	License: GPL-3.0
No account needed	No account needed
Works offline	Works offline
Official website Full listing and sources Checked October 2, 2026	Official website Full listing and sources Checked September 21, 2026

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