Connecting the Sky

[Calvin McDonald]

I need some pointers from you seasoned pano artists who stitch multi (30+) image panos with Hugin.
What is the best way to control point clear blue skies?

[Jeffrey]

there is no way. you need to place them roughly by giving them yaw/pitch/roll coordinates. placing them roughly is usually sufficient, the blender takes care of the rest.

FYI autopano pro/giga does a great job of guessing the position of such images.

[Richard Chesher]

This is a problem for lots of photographers and Jeffrey's comment about Autopano Pro/Giga is of great interest to me - that's my preferred software and I'm ashamed to admit I have not discovered the process of getting Autopano Giga to guess the position of clear blue sky images - or even images where there is just sky and sea and horizon. I resorted to buying the latest PTGui update and going through the long process of manually entering control points - and even then I got miserable results. 

Jeffrey, can you give us a link to a tutorial on how to get good stitches with blue skys or other difficult image pairs?

Thanks, Richard

[Евгений Вельдяев]

http://www.ptgui.com/support.html#5_30
This works, tested.
Evgeniy

[Richard Chesher]

I've been searching for help on this on the Autopano site and found this helpful explanation - you can import the files that include a clear blue sky so long as you have a regular shot pattern (eg. can't do it with handheld). I'm not sure if this was what Jeffrey was referring to but it does work.  Here's how:

http://www.autopano.net/wiki-en/action/view/Autopano_Giga_2.5_-_Import..._-_Gigapan

Richard

[Jeffrey]

in worst case you just drag the images around until they overlap. the blender will take care of everything ok as long as they're approximately correct.

[JimNC]

A"cheat" that I as a newbie use if there are no slow moving clouds:

Position your tripod near a building or even partly under a tree, then make sure your zenith shot includes the building or tree.

Obviously won't work at the beach or desert.

[Sam Ablott]

I've had trouble before using Hugin to stitch panos which have a featureless Zenith shot with no distiguishable points, such as a clear blue or dull overcast sky.

But I invented a little Cheat to get a round it using Photoshop.

 

Remove the problem zenith shot from the project and process the stitch without it.

Load the stitched pano into PS, be sure to alter the Canvas Size, anchored at the bottom to make the image a 1:2 aspect.

Load the problem zenith shot into PS.

Use the Filter - Distort - Polar Coordinates... Set it to "Polar to Rectangular", that will unwrap the centre of the image to the top, as in a 360x180 Lat-Long image.

Copy and Paste the zenith into the stitched pano.

Use Tansform - Scale with Snap on to make the zenith layer fill the blank top part of the pano, stretching and snapping it into the top corners, bring the bottom edge down to make sufficient overlap with the stitched pano image.

Create a Layer Mask for the zenith layer. On the layer mask drag out a vertical gradient covering the overlap of the images, hold Shift to make sure it is perfectly vertical and matches at the left and right edges.

You may adjust the blend on the layer mask further with a soft brush, but don't touch the edges or they won't match up, though you can get around that using the Offeset filter (moving only horizontally) afterwards, then retouching the edge when it's not at the edge.

In fact the horizontal offset can be used to effectivly rotate the zenith to mach the orientation of the pano.

Adjust the Levels, colour balance etc as required to match the zenith with the rest of the image.

When you have a good blend, flatten and export.