Packed JPGs are exported as PNG with filename and mime type JPG

When using a .blend file with packed images in JPG format, they are exported as PNG (making them much bigger). Also in this case it looks like the mime-type in the glTF file is image/jpeg, which is correct, just the actual exported image files are in PNG (even though their file extension is .jpg).

Example (2.80): FuseZombie.zip

You can use: File > External Data > Unpack All Into Files inside blender to get the expected JPGs.

[donmccurdy]

I haven’t looked at how this is implemented in the this repo yet, but see this code from the old exporter:

https://github.com/KhronosGroup/glTF-Blender-Exporter/blob/992b493456abba7e4d45d78f24c8b2a48e8a5a85/scripts/addons/io_scene_gltf2/gltf2_create.py#L340-L421

In particular, note the comment on blender_image.save_render, and the fact that it unfortunately applies Scene settings like exposure to the texture output (https://github.com/KhronosGroup/glTF-Blender-Exporter/issues/184).

My only strong preference here is that if an image can be left alone, it should be left alone. If the user gives us a PNG that doesn’t need to be repacked, we don’t repack it. This way, at least, we preserve the option for the user to do their packing and compression in another tool. In general I think that’s better than trying to intuit the correct format and compression settings.

[aerialglasgow]

Thanks @scurest Totally, it did dawn on me earlier importing another image, I had missed the ‘Use Alpha’ checkbox. Yes could be more intuitive on export, thanks for point this out. What an amazing app Blender is. Slowly getting to grips with it.