blog added 09/11/2006

Want to remove the tripod arm from nadir photos. Alpha channels are the answer. Using Realviz Stitcher I use the inbuilt stencil tool to remove the tripod side arms, but PTGui doesn't have such an inbuilt tool.

However, PTGui does allow you to use an alpha channel to mask out the tripod in the nadir photos.

Here is a Adobe Flash video which illustrates the process of adding alpha channel to your nadir photographs. Press play to see video.

Text description of the method.

  1. Open the two nadir photographs in Adobe Photoshop
  2. For the first photo, press on the channels tab
  3. Add new channel
  4. By default this is an alpha channel
  5. Check Selected area & 100% Opacity
  6. An all  white alpha channel appears
  7. Press on RGB channel to see nadir photograph, the alpha channel is still selected as the working channel
  8. Click on brush tool and paint on to the photograph the areas you do not want to appear in the final panorama
  9. Painted areas appear as a red coloured alpha channel
  10. Now since the other photo has the sames areas to be removed, just select Duplicate channel and copy this to the other nadir photograph
  11. Check that in this other nadir photograph that the alpha channel looks fine
  12. Save both as .tif files with alpha channel

These two resulting files can be loaded as normal into PTGui and when PTgui renders the resulting file, nothing which has been selected in the alpha channel in the above procedure will appear.