While this is likely caused by the bug documented in ticket 686, I'm opening a separate ticket just in case it's not....
When using the command Furniture > Export imported furniture to SH3F texture files saved in the resulting furniture library are resized to the nearest multiple of (depending on size) 128, 256, or 512 along each dimension. This can reduce texture image resolution, with resulting loss of information; increase image resolution[1], which sometimes introduces jaggies and other artifacts of resizing; or a combination of both.
As with earlier tickets, the seeming workaround is mnually to replace the altered texture files later, either by editing the SH3F file directly or by unzipping it, replacing the textures, and re-zipping the file. However, I've not yet been able to determine whether the texture files are resized only during export or if the imported furniture item is modified on import -- that is to say, if it makes any difference at all to correct the texture files, as SH3D may be compromising texture resolution routinely for all imported -- or possibly all imported or loaded furniture items.
To duiplicate:
After additional research, it appears this may be a hold-over from an older version of Java3D, which required texture images to have dimensions that were each a power of 2. Evidently this requirement was dropped as of version 1.5 of the library, but the model loaders may still incorporate the older algorithm. While in most cases the texture degradation that results from image resizing is minor, under some conditions it is noticeable. I've been hand-tweaking .sh3f files to incorporate the original image files -- which I now suspect ultimately made no difference, assuming SH3D insists upon enforcing the power-of-2 rule regardless of where the model originates.
See this comment on ticket 686.
See this forum thread for more information.
This is the same issue as in ticket #686. Using version 5.3 will solve this issue.