Panoramic Image Projections
If you want to get started in panoramic imagery it is useful to get at least a rough idea of the different panoramic image projections that exist and how they affect the images.
Admitting that the environment around you takes the shape of a sphere, the rectilinear projection is used when you take photos of only a portion of that sphere. This portion of the sphere is then projected on a flat surface. That’s the rectilinear projection. It is often used to stitch a rather small number of images: it is well adapted to partial panoramas and mosaic pictures.
This one will be used when the panorama does not have any data on the zenith or nadir (the poles of the sphere) – typically a single row (sometimes two rows) of images. It is the projection used for cylindrical panoramas and some larger partial panoramas that look too distorted in a rectilinear projection. It projects the portion of the sphere (the cylinder) on a flat surface (the image).
Often, when creating a partial panorama, my software would automatically choose a rectilinear projection but I found out that it would look nicer in a cylindrical projection. Don’t hesitate to play with the projections in your software to understand how they affect the image and choose the best one for your panorama! That said, most of the time the software will automatically detect the right projection for your panorama.
This projection is used to project the whole sphere on a flat surface. The result of that is an equirectangular image, with a 2:1 ratio. The width is exactly twice the height. This is logical, since it covers 360 degrees horizontally and 180° vertically. You will see that in this projection, the top and bottom of the image appear very distorted and this is perfectly normal. This is the projection you will use as a source for a full spherical panorama.
This projection can be seen as a derivative of the equirectangular projection, without distortion at the zenith and nadir. The world maps are in this projection. For panoramas, it can be useful if you want to print the image of a spherical panorama for example, or use the image on a website. But it should not be used to create interactive panoramas.
This projection is used like a breakdown of an equirectangular image (spherical panorama). The principle is that the whole sphere is turned into the 6 faces of a cube – front, right, back, left, zenith and nadir. Each of the 6 square images has a rectilinear projection.
This projection is very useful when you want to edit the image of a spherical panorama. It is not always easy to edit the warped images on an equirectangular image, and it is impossible to edit the completely distorted zenith and nadir. By breaking down this distorted imaged into 6 flat images (the rectilinear projection is the one with the less distortion), we can edit them easily.
That way, you can also very easily add a logo on the nadir image, for example. When you are done editing, you just have to convert it back to an equirectangular image and you are done!
Basically, just try to remember:
- You stitch a few images and get a partial panorama using a rectilinear projection
- Your stitch a larger partial panorama or a cylindrical panorama using the cylindrical projection
- You stitch a spherical panorama using the spherical or equirectangular projection
- You can edit an equirectangular image more easily by first converting it to a cubic projection, and then convert it back to an equirectangular image
Now let’s see what editing you must apply to your panorama to make it look good before you hit the Rendering button! Click on the link below to continue.