So when i try to export with textures and convert normal maps, some of the normal maps get converted correctly, but some of them becoming completely black.

The maps are already RGB maps?
Which model? I'll have a look.

For example Hellcat's normal map. And bunch of others too

OK...
When it is converted, the red channel which is used as the alpha mask for the ambient map is moved to the alpha channel.
If there is no mask in the red channel, when it is moved to alpha in the normal map, it makes it show up in windows explorer as black but in the preview panel, it shows up correct. The normal map will still function as a normal map. In 3DS, you may have to change the setting so its alpha is not used. I'm not sure. Been a while.

There may be a way to detect if alpha is used in the xml (visual_processed) and if not, write 1.0 in to the alpha. Let me check on that when my heart slows down. I'm in the middle of a mild AFIB attack.

Yes.. I think I can detect if the red channel is used in the compressed normal map using the visual_processed xml.

I would appreciate it if you updated with that fix =)

OK.. This is fixed. Download version 121 and install it.
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