Hi John, I'll add some general comments as others have already provide quite a few responses.
In OpenGL when you create a texture object you first have the memory for the imagery in the applications main memory, when you (via osg::Texture2D) pass that image data to OpenGL fifo, then afterwards the the driver takes the data from the fifo and creates an internal representation of that data that is suitable for passing directly to the graphics hardware. This representation may have different pixel format depending upon the hardware and the texture settings you used, and also may create mipmaps for you. Finally when the actual texture is needed on the GPU it'll be copied to local memory on the graphics card. The result of this pipeline is several copies of your data, it's not a bug, but just the way that OpenGL/hardware manages things. The Texture::setUnRefImageAfterApply(true) usage tells the OSG to unref the image after the data has been passed into the OpenGL fifo, and as long as no other references are kept to the osg::Image this data will be deleted so getting rid of one copy of the data which is why it helps. Another aspect to take into account is that files on disk that are compressed in .jpeg etc. are all much smaller than they are once they are loaded into memory. However, if you use an OpenGL compressed format such as S3TC then it'll be stored in a format that you can pass directly to OpenGL without any unpacking, here the memory usage will be consistent from disk to OSG memory to driver memory and to the GPU memory, with a caveat that if you generate mipmaps at runtime this will increase the footprint by around 40%. Robert.
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