Tag Archives: photography

Automatically removing foreign objects from photographs

Imagine that you’re on holiday, trying to photograph a famous landmark. There are sure to be other tourists around, messing up your photographs. But what if there were a way to automatically remove these interlopers from your photographs?

Here are eight photographs of the street outside a local car park, taken from the car park’s roof. In each of the photographs there is some sort of foreign object present – either a pedestrian or a car.

IMG_6524 IMG_6525 IMG_6526 IMG_6527 IMG_6528 IMG_6529 IMG_6530 IMG_6531

Below is a copy of the image, but with all of those foreign objects removed. This isn’t the result of hours of painstaking manipulation – it’s the result of running one special filter, a median layer blend, on the collection of images.

blend-resultThe median layer blend works by taking the colour values for the same pixel in each photograph and then using the median value as the value used in the output image.

For example, if the red values for the first pixel in each image were 234, 234, 197, 251, 222, 193 and 218 then the median would be 218, as it falls in the middle when they are arranged in order (193, 197, 213, 218, 222, 234, 234, 251). Because each foreign object is in a different position in each frame, the RGB values for the pixels that make them up will lie at either end of the scale, and those values will be eliminated when the median layer blend filter is applied.

It is very important that whilst taking your images that the camera remains in a fixed position; if the camera is allowed to move you end up with a blurry and oddly smooth image. The leaves in the output photograph above are slightly blurred because they were moved by the wind as the original photographs were being taken.

This technique is also very useful when taking photographs with a high ISO setting in low light. Images taken in low light are prone to noise, but because this noise is different in every image, a median layer blend filter does a very good job of removing this noise.

Here is a boring image of a London Tube network map, taken at ISO 3200 in poor light.


If we look closely, the image is very noisy.

tube-map-original-closeupBut after running ten of these images through a median layer blend filter, the noise is very satisfactorily removed.


L-R: The original noisy image and the resulting “de-noised” processed image.

I used the GIMP image processing software with the G’MIC plugin to create the images above, but I’m pretty sure similar tools are available for other packages (e.g. Photoshop).

Infrared imagery of the transport of nuclear waste

As much as I loathe Greenpeace, they’ve released some fantastic infrared imagery of nuclear waste being transported by train. The intent seems to be to try and get people to think that the casks are emitting something dangerous, but I think they do quite the opposite.

The waste is being transported in CASTOR containers from Germany to France for reprocessing and then back to Germany for reuse.

I haven’t been able to find much information from Greenpeace about the images, but I love how they’re described by National Geographic (who should know better) as Red-Hot Nuclear-Waste Train Glows in Infrared despite the fact that they’re not even close to red hot: at somewhere around 35°C they’re actually colder than the people watching them.

Images copyright Greenpeace

20 years ago today

4545 days after launch, on 14th February 1990, at a distance of six billion kilometres from Earth, the Voyager 1 probe turned its camera on the solar system for a “family portrait“.

One of the 60 individual photographs taken became one of the most famous space photographs of all time – the “Pale Blue Dot“. Midway down the brown stripe (caused by light reflecting inside the camera) you can just make out a bright spot – Earth.

Carl Sagan said of the image:

“Look again at that dot. That’s here, that’s home, that’s us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives.”

Voyager 1 is the farthest man-made object from Earth; currently it’s about 16.9 billion kilometres from Earth, 15.7 light hours away.

High speed photography

A Belgian photographer who goes by the username footopa takes some incredible high-speed photographs.

Splashes take on a whole new life – you can see surface tension pulling drips into near-perfect spheres; a bee looks positively graceful.

Of course this all requires some pretty sophisticated equipment:

You can see lots more photographs at fotoopa’s website.