/usr/share/kde4/services/qimageioplugins/rgb.desktop is in kdelibs5-data 4:4.14.16-0ubuntu3.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 | [Desktop Entry]
Type=Service
X-KDE-ServiceTypes=QImageIOPlugins
X-KDE-ImageFormat=rgb,rgba,bw,sgi
X-KDE-MimeType=image/x-rgb
X-KDE-Read=true
X-KDE-Write=true
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