Yesterday I got taken out to another archaeological site, in the Ahmor area of North Uist, this one a ‘barp’ (a mound or cairn of stones) about an hour’s walk inland from the road. I don’t really know much about shooting landscapes, but since coming to North Uist & shooting these panoramas I’ve noticed that scattered clouds make for much more interesting images than either completely clear or completely overcast skies. It also helps the panorama software, as a large expanse of flat blue or grey doesn’t have any features for the software to pick up on & match between adjacent images. Yesterday was the perfect example of this & I’m really pleased with how the panorama I shot up next to the barp came out.
So how do we go from this bunch of images…
To this 360×150 eqirectangular panorama?
I talked about the physical camera setup in a previous post so we’ll skip ahead to the stage where we have the photos taken. Because I can’t fit a graduated ND filter to the lens (what with it having a 180° diagonal FoV & a large, bulbous front element with no filter thread) I shot bracketed +1/-1 EV to capture more of the dynamic range between land & sky. So with shooting every 60° we end up with 6x sets of 3x images, for a total of 18x images. In the screenshot above I actually used 7x sets because the lighting changed a bit during shooting & I wanted to be on the safe side – I didn’t fancy repeating the 2+ hour walk through bogs to get there & back again!
We load the images into a new PTGui project, entering the focal length of the lens & the crop factor of the sensor (as the lens is mounted via an adapter & doesn’t have any electrical contacts, this information isn’t included via the EXIF data). The crop factor for the a6000 is actually 1.53x but it doesn’t seem to make any discernible difference from 1.5x.
We set the crop circle (though I’m not sure whether this is strictly necessary for a fisheye lens that fills the frame). Whilst you can just enter 0 into the ‘top’ box I’ve found that you have to manually drag the circle to set the ‘bottom’ value, as when I try to just type in 6000 it repositions the circle & affects the ‘top’ value. Zooming in to 400% or so helps to get the circle exactly right.
PTGui automatically realises that we are using bracketed exposures, so when we click [Align images…] it asks us what we want to do about it. I opt for Exposure Fusion as opposed to HDR & let PTGui align the images just in case there was any movement in the tripod.
The Panorama Editor window will then open with a preview of the panorama. When you are doing an exposure fusion this preview isn’t particularly useful, because it only shows you the ‘topmost’ image – from the PTGui website:
“Note that the panorama editor shows the warped source images, not yet merged to HDR. Since the bracketed exposures are stacked, only the topmost images are visible, in this case the ones with the longest exposure time.”
You can however choose where you want the centre of the image to be (I chose the barp itself) & then level the panorama after you’ve moved it. Obviously when viewed via a panorama viewer/app there isn’t really a ‘centre’, but choosing the centre carefully makes a difference when viewing the image flat & affects what angle you start at when using a panorama viewer/app.
At this point I go to the Optimizer tab (click the [Advanced] button at the top right of the Project Assistant tab to get access to the Optimizer tab) & change the ‘Minimize lens distortion’ setting to ‘Heavy + lens shift’ which is supposed to be good for fisheye lenses. Click [Run Optimizer] to apply the changes & if you’re input images were any good you’ll probably end up with a ‘very good’ result & won’t need to tweak anything else to get a nice stitch/blend.
The one time I did still have stitching problems at this stage, I activated the Optimizer tab’s own advanced mode & activated viewpoint correction & vertical shear after generating some extra control points at the offending area.
A useful trick for generating extra control points is to [shift]+[left click drag] to select an area, then right click & choose ‘Generate Control Points Here’, rather than creating them manually.
In the Exposure/HDR tab you can click [Fusion Settings…] to get a preview of what the blend will actually look like & tweak the target brightness & whatnot.
Then in the Create Panorama tab we can actually produce the panorama. The built in PTGui blender is by far the fastest however I’ve found that SmartBlend (installation instructions for PTGui here), whilst substantially slower, does a much better job at blending water ripples & clouds. With any luck we now have a decent looking panorama with no stitching or blending errors!
Switching to Photoshop, we can use the magic wand tool to select the black areas at the top & bottom, then the lasso tool to select the parts of the tripod that protrude into the bottom of the frame, then use content aware fill to remove them. Image > Auto Tone quickly improves the whole image very easily.
From here I used the tonal contrast feature of Color Efex Pro 4 (available as part of the Nik Collection from Google, from the same people that make the Snapseed mobile editor) to abuse the sky into a more dramatic state & bring out some more detail in the foreground rocks, while trying to keep away from the realms of overbaked HDR.
Finally, bumping up Image > Adjustments > Vibrance gives us those impossibly blue skies & green fields.
The final image is a bit ‘over the top’ compared to what I would normally do, but for viewing via a panorama viewer & especially via a HMD such as Google Cardboard (which is a potential part of this North Uist project) the in-your-face edit produces a bigger impact.
Update: Altering colour/tone/etc. of a panorama in Photoshop can cause a visible join to appear between the left & right sides of the image when viewed via a panorama viewer. Thinking about it for a moment the reason is obvious; Photoshop doesn’t know that the two sides of the image are supposed to join into a continuous image, so it doesn’t try to maintain smooth gradients between them. The quick & dirty solution to this problem is to copy & paste the whole image 3x times in a row, apply the adjustments, then crop down to just the centre copy (which can be easily done exactly using Image > Canvas Size).