Big Ben's Panorama Tutorials

Preparing the Zenith/Nadir Patches

There are many people who say that it is not necessary to patch the zenith of a panorama shot with a circular fisheye lens because it is sufficiently covered by the main images.  To some extent this is true but there are also a few problems that can be seen in many panoramas.  The main problems occur from attempting to manually edit near the top of an equirectangular image and/or variable image quality across the top of the image.

In this particular panorama there is a small hole anyway and this must be filled. Only a small portion of the upward pointing image needs to be used, but a full circular image leaves a lot of room to play with.

The nadir on the other hand presents a far greater problem. As the exposure time was 4 seconds it was not possible to hand hold the nadir shot.  Instead, the tripod was moved and the camera pointed down towards where the panorama was shot from.  This means that there are large parallax errors.  As the floor is flat we will be distorting the nadir image to fit only the region that we need to patch.  Attempting to do anything more is futile and will drive you nuts should you attempt it.

Having optimised control points for the main panorama we can now select and optimise control points between the patch images and the rest of the panorama. Select control points only from the region that you are trying to patch.

Once again, optimisation is carried out in a number of steps. Firstly, a rough optimisation to get the images close.

v v3 b3 y3 r3 p3 v4 b4 y4 r4 p4

After this, add the extra parameters to distort the image further.

v v3 b3 d3 e3 g3 t3 y3 r3 p3 v4 b4 d4 e4 g4 t4 y4 r4 p4

Since the nadir image is shot "off centre" the average pixel distance will be much higher than normal.  There's nothing that can be done about this.

So now it's time to make the final Photoshop document to begin stitching. Below is the script I used for this example.

p w1000 h500 f2 v360 u20 n"PSD_nomask" k2
m g1 i7
i n"image0.tif"
o f2 y-180 r0 p0 v178.18 a-0.2 b0.292999 c-0.2 d-0.011232 e1.10518 g9.017548 t-8.559522
i n"image1.tif"
o f2 y-55.2707 r-0.716773 p-3.25847 v178.18 a-0.2 b0.292999 c-0.2 d3.277535 e-1.229613 g9.017548 t-8.559522
i n"image2.tif"
o f2 y63.1817 r-2.13526 p-2.13937 v178.18 a-0.2 b0.292999 c-0.2 d-3.921241 e2.249382 g9.017548 t-8.559522
i n"image3.tif"
o f2 y72.8419 r174.592 p-101.992 v126.351 a0.062606 b0.615685 c-0.61264 d12.485645 e-52.668886 g111.675616 t-106.705916
i n"image4.tif"
o f2 y-112.876 r-67.2378 p90.0676 v149.727 a-0.2 b0.448478 c-0.2 d-2.831832 e2.15134 g6.433032 t0.048377

Rather than let PTStitcher produce masks for the seams I prefer to edit the masks manually from scratch. If the seams were going to be OK using just PTStitcher then it is very easy to edit the masks.  If the seams need special attention, then it easier to start from unmasked images. Either way, after editing the masks of the main panorama, discard the mask of the bottom layer and the lower patch layer to end up with something like this...

Main Panorama
Patch Layers

Merge the two patch layers together and then merge the layers for the main panorama, leaving only two layers representing two panoramas. Note that the nadir patch does not look like it fits properly because it has been distorted to fit only a portion of the image. This is nothing to worry about.