More fun with long exposure stacking of photos

A few months ago I experimented with Imagemagick by using it to merge very similar photos of flowing water to give the impression of a longer exposure.

Here are a few more examples.

By merging a series of thirty photos taken two seconds apart I created a pleasing image that looks like a sixty second exposure. The day I took these photo was overcast and dull, but not dark enough to do an actual long exposure like that without the help of some fairly dark filters. I used the intervalometer in Magic Lantern to shoot this so I didn’t even need a remote release. My camera did all the work! This was created using the following Imagemagick command line:

convert *.jpg -average average.jpg




I combined 60 long exposure shots of the night sky in the mountains of Utah (during the Automattic Grand Meetup a few weeks ago) to create a single long exposure of the stars moving through the sky. Thanks mkaz for publishing this post on interval shooting where I got this command line:

convert *.jpg -evaluate-sequence max combined.jpg




Finally, another series of sixty shots taken in Utah. The same convert command line was used to process these.




In the image above I should have cloned out the wires in the bottom left of the image. Lightroom makes it easy to make the same modifications to every image. Work on one image, then select all the ones you need and click “Sync Settings”.

It can be frustrating taking these types of photos as your camera is shooting a long series of very ordinary shots, and the final result can’t be seen until the images are processed correctly but it’s certainly worth it.

Aperture ƒ/8
Camera Canon EOS 6D
Focal length 24mm
ISO 100
Shutter speed 1/50s
Lightroom - dng

The Limits of Lightroom’s Smart Previews

I just stretched the limits of Lightroom’s Smart Previews this morning.

After editing the following image I decided to see what it looked like as a smart preview. I pushed the image quite a bit, exposing the colour in the sky as the sun set behind me in Lanzarote a few days ago.

Lightroom - original image

The original image is dull and lacks contrast but with a little work I was able to expose the lovely shades of magenta and orange present. Here’s what it looked like when Lightroom was editing a DNG file:

Lightroom - dng

But when I removed the file and Lightroom had to use the smart preview this is what that lovely colour gradient looked like:

Lightroom - smart preview

There’s visible compression artefacts visible that aren’t in the original and it looks more pronounced in Lightroom. I didn’t push the image too much, but these sort of artefacts can be seen in Jpeg images of smooth colour gradients like a blue sky has. They’re really visible if you push the contrast at all, or modify the colours in the gradient like I did with this image.

Smart previews create images that are 2500px wide or tall which is a good compromise between full size RAW and not being able to edit the image at all, but on a high resolution screen like a Macbook Retina screen you won’t be able to zoom much.

I will continue to use smart previews. My 1TB+ photo archive can be crunched down to less than 200GB which is within the reach of a laptop, and still leave free space. Once I plug my external drive back in and fire up Lightroom I can then export the images and be sure that the final image is what I want.