SP.747 Final ProjectMatt PapiMay 17, 2007MotivationMy final project, a 160◦HDR panorama of the Boston skyline that blends day to dusk tonight, was primarily motivated by a desire for something that was interesting to look at andinteresting to create. The city as seen walking east along Memorial Drive is one of my favoriteviews, and I’ve been fascinated by the concept of panoramas – especially by the process ofmaking them without any special equipment – so the choice of subject was natural. Theidea for a day-to-night transition came mostly from my inability to choose the time of dayfor shooting the panorama. I wanted the final project to be technically challenging but notheavily altered, and blending the scene seemed to satisfy both criteria. HDRI was used (andexcessive tonemapping – the “surreal” look – was avoided) to attempt to give the scene amore natural feel.TechniqueThe creation process consisted of four major steps: shooting, HDRI, stitching, and blending.ShootingThe images were shot using an Olympus E500 DSLR camera with a telephoto lens at 25mm.The camera was placed on a tripod along the edge of the Charles river; I marked the spotwith chalk, as I’d be shooting in three different sessions. Lens choice resulted in a tradeoffbetween image detail and sharpness: a longer focal length means more images composing thepanorama and a higher resolution overall, but wind and long exp osures caused longer focallengths to produce blurrier images overall. 25mm was the shortest focal length I could reallyuse – any more and I would have had enough images to exceed the limits of the computersI was working with.After several rounds of shooting in three sessions – one 1.5 hours before sunset, one atsunset, and one 1.5 hours after sunse t – a total of 48 images were retained. Since HDRI wasbeing used, each piece of the panorama had to b e shot three times: one overexposed, onecorrectly exposed, and one underexposed. HDRI techniques merge these three exposures1into a single image to retain details that would normally be in blown-out or shadowed partsof a correct exposure, thus giving a better approximation of a scene. Three images wereshot for day, six for dusk, and seven for night (times three exposures each, yielding 48).The difference in the number of shots in each session was due to the fact that I didn’t knowexactly where the dusk/night overlap should occur – it would largely depend on how mucheffect the Fenway lights had on the photographs. So that HDRI could be employed, theimages were shot on the highest resolution in raw format; so that there would be as littlenoise as possible, everything was shot at ISO 100 (as a result, some of the night overexposuresrequired shutter speeds of over 30 seconds!).HDRIUsing the “Merge to HDR” feature in Photoshop CS2, each set of three exposures wasconverted to a 32-bit HDR image. I avoided performing excessive tonemapping on theimages; instead, when converting to 8-bit, I used histogram equalization (stretching theinput image’s dynamic range to fill that of the output image) for the day and dusk images,and highlighting compression for the night images. This process was very straightforward andworked well (though at some point I’d like to play with HDR tools that are less automatedand have more features).Figure 1: Three exposures and the merged HDR image.StitchingStitching was performed using the Hugin tool, which is Free Software and is available fromhttp://hugin.sourceforge.net. Hugin has several handy features, including image fea-2ture detection to help automatically align, rotate, and skew images, and a high-qualityblending tool for getting rid of the seams between component images. The day, dusk, andnight HDR images were stitched into three separate panoramas. I used the equirectangu-lar proj ection, since it seemed to give the straightest horizon line and the least amount ofdistortion for all the panoramas.Figure 2: The day, dusk, and night stitched images.BlendingUsing the Gimp (also Free Software; http://gimp.org), I created an image in which eachof the three panoramas was a layer. Since the dusk panorama was to be the central one, itwas placed as the background; for day and night, an opaque-to-transparent gradient layermask was created (with the gradient in the overlap region). Then, the day and night layershad to b e scaled, rotated, and moved to align as closely as possible with the backgrounddusk layer. This was definitely the hardest part of the entire process, since a bit of blur hadaccumulated from HDR merging and stitching, and since the panoramas were shot in threesessions (the camera and tripod setup was disassembled and reassembled between each one).After blending, I cropped the image (the original stitched images were slightly skewed fromthe projection) and made some minor adjustments to increase the sharpness of the image.3Figure 3: The final blended