Stitched Panoramas


Stitching is process of joining together two or more images to form a larger image that appears continuous. The word "panorama" sometimes conjures up the idea of a long skinny image that shows most of the horizon. That type of panorama can be interesting, but it is a special case.  Merely wide angle or very wide angle photography is more important for common use.  Sometimes you may want a wide angle to show a group of people in a room or other confined space, so you need the wide angle just to get the job done.  For scenic photography, a wide angle enhances the feeling of what it was like to have been there. That may be because we naturally see in wide angle. Normal vision is not quite 180 degrees. With respect to human vision, a ca,era's so-called normal lens is really a moderate telephoto. It's true that even though we have a wide field of vision, we have a central spot of high acuity that we move to view individual objects in detail. The momentary attention to individual objects could be analogous to taking a snapshots. Nonetheless, our eye roams around in the full field of view to pick out those items of interest. A wide angle photography allows the viewer of the photograph to experience the exploration process and to fit the elements of the scene into the whole.

Here is an example of two photos taken with a pocket camera and stitched into one. The museum sign was not damaged in a storm; it is art. Notice the change in perspective, the way vertical lines converge towards the top, between the separate images and the stitched image. Perspective change is a problem for the stitching process.

Museum, left image   Museum, right image

Museum, stitched

Because wide angle images are designed to be explored, they are more effective when viewed large. Click the stitched example to enlarge it. It will adjust to fill a window up to 1280 pixels wide.

For the reasons cited, a wide angle image is often the best. Not always, but often. Photos of individuals or small groups of people are best taken zoomed in. Photos of a merganser or the setting sun demand an extreme telephoto. If you mainly take portraits or birds or sunsets then a wide angle will be an exception for you, but for many people wide angle should be the rule for capturing good images. The problem is that to our knowledge no pocket camera has a decent wide angle capability. That is probably because most people take out their camera only a few times a year and mainly take pictures of friends and family. Add-on lens attachments are available for some pocket cameras to increase the field of view, but they introduce unacceptable distortion, and the add-on sticks out to make the camera too bulky to fit in a pocket.

If you are going to carry a camera separately, you might as well step up to one that has interchangeable lenses, but even good wide angle lenses have limits. The basic problem is that the lens is trying to put a circular world on a flat image sensor (like film) and that produces annoying distortion. The bottom line is that the stitching technique is often useful, even if you have shelled out for a spiffy camera.

How to Stitch

The technique of splicing together two or more images is the same whether the frames are stacked horizontally or vertically. However, vertical stitching has advantages that are easily overlooked.  Vertical stitching can overcome common problems of getting a whole scene in focus and keeping the sky from being overexposed. 

The main draw for stitching is to achieve a wide field of view with the modest lens capabilities of a pocket camera. Sometimes we associate stitching with long thin panoramas.  Stacking to frames vertically produces an image with a more conventional aspect ratio. Here are two images taken in Oakland's Chinatown, brought up in the Full Edit mode of Photoshop Elements:

Original Oakland Chinatown images

From the File menu, select New > Photomerge Panorama ...

Menu for making a panorama

The Photomerge window pops up.  Auto usually works for the Layout option, but choosing Interactive Layout makes it possible to fiddle, if necessary, without backing up a step. It will attempt to align automatically nonetheless. We only had the two files we wanted opened, so Add Open Files selects them to make the panorama.

Get files for panorama

It's lucky we selected the Interactive Layout option, because we had to click on the Perspective option in the next step to get two images to match up for stitching. If the stitching still doesn't work, try the Cylindrical option. The stitching then proceeds and stitched image is returned to the editing space. Note how the bottom image was distorted by the Photomerge software to achieve the match up for stitching. The image is returned in layers, so use Layers > Flatten Image to get to a normal image that can be saved as a JPG:

flatten

The crop tool is then used to make the image rectangular.  

Oakland chinatown vertical stitched

So maybe it is still not a prizewinner, but compared to either of the originals, it is more interesting and gives a better sense of what it was like to have been there. The pocket camera with the equivalent of a 35mm wide angle produced, with some effort, a result equivalent to what might have been obtained with about a 24 mm lens. The image also gained about a 50% more pixels as well.

Nothing  Should Move in the Stitch Region

If something moves in the overlap region between the taking of the two frames then the two images will not splice neatly. It was not windy, so the leaves did not move. If the leaves were moving, the bottom image could have been cropped to eliminate the leaves, leaving the immobile red facade as the region of overlap. Having people or cars moving in the lower image and leaves moving in the upper image would not cause a problem so long as the region of overlap had nothing that moved. So watch for moving foliage, people, and cars ... and the really nasty one, moving waves in seascapes.

Focus and Dynamic Range Advantages

The images for a stitched panorama must be taken at the same zoom magnification or they won't match up. However, the exposure and focus distance of the two images can be different, and that offers interesting possibilities.  Tilting the lens on a view camera is one way to get an image that is in focus from a foot away all the way to the horizon. Another way is to approximate by taking a closeup of the foreground and stitching it to a shot that covers, say, six feet to the horizon.

An automatic exposure setting will adjust to produce a proper blue sky when the sky fills the frame. If the image is half sky, the average exposure for the scene may result in the sky being pale and overexposed. HDR imaging solves this problem, but stitching a sky photo to a ground photo can also work well. The overlap region should be around the horizon. The exposure mechanism is automatic, so there is nothing to do except point the camera for the two exposures. If there is ocean or moving grass in the lower frame, cropping the top image exactly to the horizon or to just above the horizon may facilitate the software registering the two images.

Here is a stitched image taken from the Saddle Road looking towards Mauna Loa on the Island of Hawaii:

Saddle Road vertical stitch

A closeup view of the near foreground was stitched to an image that included the horizon to provide a sharp image over a large range of distances. The perspective give the eye a lot to explore in the image.
copyright QuickShotArtist.com