Map to cylinder adding random Clear patches

[n4mwd]

I am trying to restore an old photo that includes a coffee can in the foreground.  I was able to find several donor images of the can I need.  These were rectangularized, flattened, and then stitched together to make a large flat version of the complete can.  The result isn't perfect, but should be fine for what I'm doing.

   


I then used the FILTERS->MAP->MAP OBJECT->Cylinder  filter to make a new 3D cylinder out of it that I could rotate into the proper orientation.  The problem, as pointed out by the arrows, is that several sections of the new cylinder are transparent.  The original flat image has no transparencies.


   

So what is going on here?  How do I make a cylinder with no random transparencies?

[rich2005]

(Yesterday, 05:23 PM)n4mwd Wrote: I am trying to restore an old photo that includes a coffee can in the foreground.  I was able to find several donor images of the can I need.  These were rectangularized, flattened, and then stitched together to make a large flat version of the complete can.  The result isn't perfect, but should be fine for what I'm doing.




I then used the FILTERS->MAP->MAP OBJECT->Cylinder  filter to make a new 3D cylinder out of it that I could rotate into the proper orientation.  The problem, as pointed out by the arrows, is that several sections of the new cylinder are transparent.  The original flat image has no transparencies.




So what is going on here?  How do I make a cylinder with no random transparencies?

Who knows except yourself. I can not reproduce your transparency. This a half scale result (full size png too large to post)

   

Because there are many settings these screenshots of all the dialogues. How do they compare with yours ? 
Note it works best with a square base image . The white image is the top and bottom.

   

[n4mwd]

I guess I have found the answer  on my own.  For those who are curious, there is a bug in Gimp 2.10.

The workaround seems to be to remove the alpha channel before using this tool.  While there are no transparent spots in the original flat image, apparently the presence of an alpha layer causes gimp to fail to render the cylinder image properly.

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(Yesterday, 06:44 PM)rich2005 Wrote: Who knows except yourself. I can not reproduce your transparency. This a half scale result (full size png too large to post)

Because there are many settings these screenshots of all the dialogues. How do they compare with yours ? 
Note it works best with a square base image . The white image is the top and bottom.

Thanks for your reply.  It looks like we just posted simultaneously.  As stated below, the problem is a bug in gimp 2.10.
I don't get the error if I delete the alpha channel before using the tool.  It should not make a difference.

In your case, the files I uploaded were JPG files to keep the size down.  JPG doesn't usually have an alpha channel so you wouldn't see the problem. 

I tried adding the alpha channel back and the problem didn't come back.  So there apparently was something flakey about the original PNG image that had the alpha channel.

Going back to the original PNG, I used Alpha To Selection, then Add Layer Mask(Selection) then Show Layer Mask.  This was to see if there was anything on the alpha layer and there wasn't.

If you are curious, I can post the PNG that I can replicate the problem with.  It is 6.6MB.