More Tilt-Shift Trickery… with Bing Maps Birdseye

A few weeks ago, John Nelson of IDV Solutions posted an infographic describing how to simulate tilt-shift photography using aerial imagery from Bing Maps. You can see his guide on visual.ly.

While using Bing Maps imagery as a source for pseudo-tilt-shift imagery is an interesting idea, I think John has missed a trick, because he only uses Bing Maps 2d aerial imagery. Aerial imagery is shot looking straight down from above, so that all the features in the image lie on an essentially flat plane parallel to the lens. Therefore, there’s no reason to expect that features lying further away from the focal point of the image would be any more out of focus than those in the centre (even if this were a scene from a model village, which is what the tilt-shift effect is generally used to simulate).

I think that a much better effect could be produced by using Bing Maps birdseye imagery, which is shot at an oblique angle. Therefore, blurring can be applied to mimic the varying depth of field you’d get throughout the image if this were a close-up shot of a miniature scene. Another point to note is that the plane of focus does not have to be aligned to the plane of the image (i.e. the part of the image that is in sharp focus does not have to be a perfectly horizontal band). It can sometimes be more effective to use an oblique plane of focus -that’s what the “tilt” bit of a tilt-shift lens enables you to achieve.

To demonstrate, here’s some quick pseudo tilt-shift Bing Maps birdseye images I made using the technique described in my blog post from last year. They give the impression that the whole world is one big model village….

I’m now wondering if it would be possible to create a “dynamic” tilt-shift filter in HTML5 or Silverlight to apply this effect in realtime as you panned across Bing Maps in birdseye view. Hmmm…..

Tilt Shift Lens Effects and Toy Trombonists

Watching the Eurovision Song Contest with friends last Saturday (don’t ask – it’s a family tradition…), we noticed the extensive use of tilt-shift lens effects in the opening “postcard” video preceding each act. Tilt-shift lenses can be adjusted (well, tilted, specifically) to deform the field of focus you’d get from a conventional lens, keeping the subject sharp while hyper-accentuating the blurring in parts of the image that are out of focus.

When applied to a picture shot from above, the effect created by such lenses makes the entire image appear to be a miniature toy model, such as in this image from the introductory video to Estonia’s song entry (it looks even more impressive when seen as part of a moving video):

Dedicated tilt shift lenses, such as the Nikon PC-E NIKKOR 24mm F3.5D ED lens pictured below are expensive and difficult to use,  and generally only used in dedicated fields of architecture photography.

However, it’s possible to mimic the effect of a tilt-shift lens digitally using Photoshop.

To try this out, I chose a detail from a snap I’d taken from the recent Norfolk and Norwich Festival, showing the excellent “Always Drinking” marching funk band. I chose to base the image on just the trombonist and the crowd behind him, highlighted here:

I wanted to create the impression that the trombonist and the people behind him were die-cast figures, placed in a “town carnival” scene of a model village. So, here’s what I did:

1. First, crop the image and placed it in a new layer.
2. Create a new layer mask (Layer > Layer Mask > Reveal All). This layer was going to be used to define an artificial “depth” map to apply when selectively blurring the image. There are several good tutorials on the internet that explain how to create a layer mask for tilt shift effects using the gradient tool (such as this one), so I won’t repeat what they say here. However, while a basic gradient works well when the focal depth of the image varies consistently with the angle of the photograph (which is generally the case in a view taken looking down at a subject from a distance), I found it wasn’t going to work so well with this subject because it was taken at a much more shallow angle. Instead, I started off with a broad reflective gradient that defined an area that was to be mostly in focus across the middle of the image, and then manually edited the mask with a semi-opaque brush to bring out the trombonist. Areas that were masked (i.e. those shown in white in the layer mask thumbnail, and opaque in the main image) were to be in focus, while those unmasked would be blurred. After a few minutes my layer mask looked like this:
3. Now, selecting the layer itself rather than the mask, I applied a lens blur filter, using the layer mask as a depth map.
4. To make my trombonist look more like a painted toy, I increased the saturation by 20, and lightened the image slightly. I also narrowed the extremes of the input levels in the image and created a slight S-shape curve to emphasise contrast.
5. The result is shown below. It’s certainly not perfect, but I’m quite pleased with it as my first attempt at this technique, and I think it creates the general impression I was hoping to achieve – I could probably imagine this as a detail from some amazing model village, with a Hornby model train about to race around the outside… it also only took me a short time to do – with more effort I could have refined the mask further.