Ultra High-Resolution Images From Stitched Image Mosaics

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Years ago I used large format cameras for landscape and scenic photography: a vintage 1950s Crown Graphic 4"x5" press camera and a massive, heavy Linhof 4"x5" studio camera. I had a black and white darkroom in my basement and loaded and processed my own sheet film for these cameras. Big enlargements from 4"x5" negatives can be incredibly sharp and grain-free, much finer than even the sharpest 35mm transparency or negative. The problem with these cameras, at least for me, was the sheer inconvenience of traveling with them. They are big, very big, and heavy, very heavy. And the the sheet film must be loaded into bulky holders, two sheets per holder. A stack of four or five film holders for my Crown Graphic, for eight or ten exposures, probably takes up about as much room as a twenty-roll brick of Fuji Velvia 35mm film canisters. I could take boxes of sheet film and a few holders and reload them in the field, but this really requires a dust-free, completely dark environment to do successfully. Perhaps I just wasn't committed enough to the principles of large format landscape photography, but due to these hassle factors, most of my large format exposures were taken within a few miles of my home.

More recently, in a quest to achieve similar high-resolution results with portable, travel-friendly 35mm cameras, I've begun using image-stitching software to assemble huge tiled and panoramic images. There are a number of commercial software packages which can assemble such images, some with more features and capabilities than others. I actually prefer using a free image stitching software package called Panorama Tools. Its ease of use is definitely on the difficult end of the scale, but it is probably the most feature-rich and powerful stitcher currently available, free or otherwise. There are very good tutorials on using Panorama Tools already published on the internet elsewhere, so rather than provide another tutorial on using a particular stitching package, I'll simply show a case study on producing a stitched image mosaic.

I make a distinction between an image mosaic and a stitched panoramic image. By mosaic, I mean a grid (two or more rows of images) of photographs that, when stitched together, resemble the field of view of a single, rectilinear wide-angle lens. By stitched panoramic image I mean a single row of photographs (actually you could use a multi-row grid of photographs as well) that, when stitched together, resemble the panoramic image created by a rotating-lens panoramic camera (like the RoundShot Super 35). Incidentally, Panorama Tools has options to build a stitched image using either lens type, rectilinear (single, wide-angle lens) or cylindrical (rotating-lens which 'paints' an image onto a strip of film as it rotates, as if the film-plane were curved like the inside of a cylinder). In the example Atlanta skyline mosaic below, I've chosen to use a rectilinear projection: the final result approximates shooting the same scene with a large-format camera with a wide-angle lens.

The first step in creating the mosaic is to shoot a series of photographs with overlapping fields of view. Here I've overlapped each adjacent pair of images by perhaps 25%. This shoot was done after sundown and the low light necessitated long shutter speeds. You may notice that the car headlight and taillight streaks in the individual frames are often cut off by the frame boundaries. When I stitched together the final image, I had to hand-edit some regions of the frame to hide these discontinuities.

Raw photo mosaic of Atlanta Skyline

The next image shows a rough assemblage of the raw frames. You can plainly see that, in order to seamlessly stitch together the individual frames, each image must be warped slightly and any color-balance and tone differences between pairs of images must be smoothed out. The stitching software accomplishes this by matching up corresponding image features in pairs of images, figuring out how the camera lens distorted each image (slight barrel distortion in this case), un-distorting each image, and finally merging all the images together into a single frame by feathering the boundaries between adjacent images.

Rough stitch of Atlanta Skyline

The finished image below has had tone and contrast tweaks and a moon image composited into the sky (the skyline scene and the bright moon need widely different camera exposures and therefore couldn't be captured in a single frame). The resulting image is around 30 megapixels in size. Compare this to a single 6 megapixel frame from the Nikon D1X camera used to take the tiled images! A full-resolution crop shows that the text on the distant road sign is quite legible. This image makes very sharp, vibrant 40" x 36" prints.

Atlanta Skyline Full-resolution crop from Atlanta Skyline image

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