Chapter 06_
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Efficient overlaps
Keep the settings consistent
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For this view of an art installation in a gallery, four frames were overlapped by approximately 40%. There is ample detail in the scene for the stitching software to recognize content.
There are three stages in stitching. First, the software has to find corresponding areas of content in adjoining images and warp them so that they are in perfect register. Second, it has to blend the tones so that they match smoothly. Last, it combines the multiple images as one. The first step relies on there being enough of an overlap between neighboring frames for the content to be recognized. That means enough corresponding points in each image. Ideally, you want enough of an overlap for this without overdoing it and shooting more frames than necessary. There is no hard and fast rule on this, partly because different software varies in its ability to do the matching automatically, but more because the quality of the detail depends on the scene itself. Sharp detail is best, and stitchers understandably have difficulty with featureless areas like sky and white walls. Around a 40% overlap is fairly safe, but you might want to vary this according to how detailed the scene is. Personally, I like to keep things simple and consistent by overlapping just under half. In practice, this means rotating between frames in such a way that an object on the edge of the frame in one shot is almost in the middle of the next, and so on. As I always do this the same way, I can shoot a panorama quickly and without having to think very much, and that’s not bad.
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StitcherUnlimited - Untitled.rzs*
The second stage in the stitching procedure, as I described on the previous pages, is the blending, and this involves color as well as tone. If you keep the white balance the same for all the frames, this will make life easier for the stitching software. And this applies to other settings as well, including exposure. For this reason, the standard advice when shooting a sequence for stitching is to switch to manual and keep the settings consistent. This might well involve doing a dry run and checking what the settings should be for each frame in the sequence. As 360º panoramas are quite likely to include light sources in shot (especially outdoors on a sunny day), this can mean that a single exposure and color setting might cause out-of-range values in shadows and/or highlights. In other words, it exceeds the dynamic range of the camera (see Tip #15), and this is quite common. The usual solution in this case is to take a sequence of exposures for each frame, and then combine the results either through exposure blending or HDR. That said, if you shoot Raw it doesn’t matter very much, other than the extra time making color adjustments in the Raw converter. An interesting and useful technique is to change the color balance progressively. Imagine a scene in which the color temperature varies, such as from daylight on the window side of a room, to tungsten on the other. In postproduction you might well consider trying to normalize the balance, but if you were to select Auto white balance when you shoot a stitched sequence, the software will make an attempt at doing the blending automatically.
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1-8 An example of going against the standard advice for consistent white-balance settings. The four source frames were shot in Raw, but also with Auto WB, and so the color temperature changed from left to right [1 = 5500K, 2 = 4500K, 3 = 4000K, 4 = 3300K]. The result, once the stitching software had blended them, is a progressive change which, to my mind, gives a better balance between the blueish exterior and yellowish interior. Final retouching using Replace Color took care of the reddish tinge on the right side of the window frame. For comparison, here is a stitch using a consistent, tungsten WB.
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