Friday, June 21, 2013

Tavy railway bridge panorama

I'm not a practiced shooter of panoramic pictures but some subjects cry out for the ultra wide treatment.  A couple of weeks ago I went to Warleigh Point on the banks of the Tamar near Plymouth.  The aim was to shoot insects in the nature reserve (I did) but I couldn't resist shooting the railway bridge which crosses the Tavy where the Tavy and Tamar join.

Railway bridge over the River Tavy, Devon.  Click to enlarge.
One of the benefits of digital photography is the ability to stitch multiple shots together in software rather than requiring a dedicated panoramic camera such as the Hasselblad XPan back in the days of film.  In this case the bridge, set against a background of the rolling hills of the Tamar valley, needed a stitched panorama to avoid either cropping top and bottom or the inclusion of large amounts of sky or estuary mud if I'd tried to fit the whole width in a single frame.

Out came the tripod, on went the 180mm macro to get the right framing, the camera was set to manual exposure at 1/400 and f9 to avoid variations in brightness across the panorama, and I took 12 shots, tracking from left to right with decent overlap between the shots to make the stitching easier.

Back at my desk I processed the RAW files with identical recipes, batch converted to JPEGs and stitched the 12 files using Canon Photostitch (free with Canon DSLRs).  Sounds easy.  It's not.  You can't rely on the autostitching so each merge seam has to be merged using multiple points to get the best placement.  12 shots is eleven merge seams.  Get one out and it throws off your other merges.  And to check it's necessary to save the merge, check the resulting JPEG - and start again if a merge hasn't worked correctly.  I spent a little over an hour getting it right to produce a seamless panorama.  It may be easier in more advanced programs but I work with what I've got.

Even that wasn't the end of the process.  The resulting panorama needed straightening tp produce the correct alignment.  I use GIMP as my photo editor and this has a tool to set the correct angle.  In the case the alignment was easy.  I simply aligned the middle four spans at the point they met the river.  Just like using a spirit level.  A final crop and save produced a 25875 x 2947 px image, reduced by Blogger to 1600 x 182 for inclusion on this post.

I think it works well - and the original preserves all the detail inherent in a high resolution shot.  Detail like this of one of the supports.  Click for the 100% crop.

100% crop from Tavy railway bridge panorama
Now to find someone who can print it.  At ~300dpi it should work out to 90 x 10in / 225 x 25cm, even larger if I take the dpi down to 250 or even 200.  On second thoughts I'm not sure I've got that much wall space - especially if I repeat the process with the tide in.


I've added a 4000px wide image to Flickr.  Click here to view.  Right click on the Flickr image and choose original from the size options to see the larger image.

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