It's a process in which all the images taken for a panorama gets seamlessly stitched together to form a larger photograph, which is extreme wide angle and is projected on a curved surface with the 'observer' inside.
Remember the snow-globe model?
If the photographs taken from standing inside the dome, are combined to make one very large image, and then the image is projected on some similar or almost similar dome shaped curved object, and if the 'observer' is somewhere inside the projection dome, then he will see the same scene seen by the photographer who was on the spot. So this is a convincing process in which it is possible to fool an observers sense of vision, and hence brain to make him believe, that he is standing inside the actual scene! So this is a successful process of achieving virtual reality. You will know what I mean if you have been inside a Pan-hemispheric Cinema, popularly known as 'Space-theaters'. In this cinema the entire huge dome is a cinema screen, and the audience sits inside the dome. If it is a film shot in true pan-hemispheric way, with true fish eye lenses and all the large format film supporting gears, (and not a movie made for I-max format) then when it is projected inside the space-theater dome, it will produce the true perspective correct images, that will give the audience excellent illusion of being at the spot- be it land, up in the sky, or underwater, and even the feeling of movement at times! I-max format films also produce similar effects, but the straight line always gets curved at the edges because of the curvature of the screen.
The Pan-hemispheric cinema
in Kolkata Science City
What goes on inside the pan-hemispheric theater?
So what exactly is image projection? What are the ways to do them?
Image projection is the process of mapping a flat image into a curved surface. This is where I found answer to my first problem (where I forgot to consider the curvature of the dome). The photographs I'm taking are coming as rectangular slices of the scene, but ask a cartographer, he'll know exactly how to put back these flat slices on the curved surface on which I want to rearrange them. On the curved surface, the rectangular slices will no longer be rectangular, in the center they will be slightly curved at the edges, but overall they will be very near to being a rectangle. But at the polar regions, the distortion becomes larger and hence will be more difficult to compensate (see image below). So image projection includes taking all the photographs and projecting them on the correct slices over the globe, and in the process introducing correct amount of distortion on the respective photographs. And image stitching will be the process of stitching these photographs together seamlessly.
My search yielded that there are many softwares out in the market which can efficiently do this job. I tried out two of them. One of them is 'PTGUI Pro' which is very light and extremely efficient. There's another one called 'Hugin' which is free and open source. However Hugin is still under construction and has got some bugs yet to be fixed.
One good thing about these software is that they can automatically read the 'EXIF data' from the camera and correct the photographs accordingly. The Exif data includes the FOV of the photograph and out of that it calculates the barrel distortion of the lens. So my second problem which was the distortion of the lens, is also taken care of now.
I wasted no more time in trying this software out on the same photographs I took from my terrace.
The result was awesome!
Ofcourse this is not an effectively projectable panorama as you can see that many pieces from the sky and ground are missing, so anyways the virtual tour will not be complete, but still one can see how nicely the software stitched the photographs together, blended them, and has introduced the correct amount of distortion into the scene.
Actually this distortion is introduced individually into each of the photographs, and then the distortion in the whole scene is calculated while the stitching goes on. To understand how this distortions takes place, consider the diagram given below.
Now that I found the correct software, I thought of creating a new complete panorama.
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