PTGui’s inception and intended use revolves about the entrance pupil… but sometimes folks (myself included) want to try pushing this amazing bit of software to do other things. For example, a client loans me a large map and allows it to be copied. Using only a small flatbed scanner and sufficient overlapping scanned images, PTGui stitches and blends them together perfectly.

Stitching images of two dimensional objects like drawings and maps is one thing, but the stitching together of images of three dimensional objects require consideration of the station point before a single click of the camera is heard. Regardless of the field of view (focal length of 10mm or 1000mm), it is the station point of the observer , along with the orientation (vertically plumb or angled) of the picture plane / film plane / censor plane which determines the perspective for that image. The focal length of the lens and its effect on straight / parallel lines appearing to curve (or not) is something PTGui is quite good in figuring out; however, it’s up to the photographer to determine the scene’s perspective.

For these mural experiments I kept it simple: one-point perspective shots. In the first example, three separate images were taken with the censor plane vertically plumb and square to / parallel with the stores along the northerly side of Main Street. Placement of the station point was deliberately in front of the little one-point scenes flanking the store and the third one-point scene immediately in front of the store’s entrance. All station points were along a common line; the face of curb on the south side of Main Street. Everything else was treated like a regular spherical pano; i.e., manual focus, manual white balance, manual exposure, etc. And for the curious; all experiments were done using 24mm on a full frame camera.

3-shot pano

Blending images to include / exclude perspective of neighboring scenes illustrated with seams in red in the PTGui screen capture above.

Right-click on image to the left and Open link in New Tab or Window to see the largish version (3773 x 1020).

Station point elevation becomes an increasingly important consideration if the goal is to maintain a single horizon line and although in this example the camera was elevated at a constant height above grade for each setup and the slope of grade was appreciable (which resulted in three different horizon lines) the only noticeable frame of reference is the disjointed condensation trail seen in an otherwise featureless sky. The trees’ interruption of this feature is almost enough to not worry about it cloning the con trail out, but then it wouldn’t be as effective in illustrating this discussion

6-shot pano

Some elements from a neighboring shot require d a little extra attention to masking since it’s included in the result. For example, looking northward down Franklin Street toward City Hall there are two street lamps flanking the view with one of them (the one on the right) protruding into the primary Franklin Street one-point perspective shot. Detail of the lamp post area mask shown on the left (click image for larger view) with an overview of the masks used in this 6-shot series shown below .

Right-click on image to the left and Open link in New Tab or Window to see the largish version (6759 x 1284).

Some features like the painted cross walk stripes are better cloned out, but here again are left in for these experiments to highlight the need for consideration of station point locations to minimize or eliminate foreground elements that arouse the sense that the perspective looks whacked.