Colour Calibration


How does this picture look to you? I can guarantee one thing – it looks different to me, and to anyone else viewing it.

I’m talking specifically about the colours. I’ve viewed this picture on several screens – my computer, my phone, a couple of different tablets and another PC – and the colours were different on each. On the other PC, in particular, the colours were far less warm, and the lower part of the sky was a brighter cyan.

On my Mac, the colours are quite warm with a hint of a magenta cast in the clouds. On the tablets the colours are also quite warm. On the Windows PC, the cast disappeared and the overall colour was colder.

It’s a problem for photographers. A keen photographer may invest in colour calibration equipment to get the colours just right. That’s important when printing, so that soft proofs on screen are as accurate a reflection as possible of the final print. How often do we actually print though? I would imagine I’m like the majority of amateur photographers these days in that my photos are only seen on screen, and rarely printed.

That, then, is the problem with colour photography on the internet. You can tweak the colours all you like to get something that looks right to you, but have no control over how it’s seen by anyone else. No wonder I convert a lot of my photos to black and white!

Experimenting with star trails

20130814_0001-EditWe’ve had a couple of clear nights recently and with the prospect of seeing the Perseid meteor shower I’ve been spending some time in the garden of an evening. I didn’t have much joy – maybe two or three over the course of a couple of nights.

While I was out there, I decided to set the camera up and have a go at star trails. I was mainly aiming to try out the techniques and see what happened. I figured the level of light pollution where I live would rule out getting anything worthwhile, and I was pretty much right.

20130813_0007I started off with a few 30 second exposures, such as the one on the left here, just to get a feel for what I could capture. At that duration, with the aperture wide open, the stars are quite clear but the street light is starting to become obtrusive. The camera has picked up far more stars than were visible with the naked eye.

I tried the stack approach of taking a series of exposures of around five minutes each with a view to combining them in Photoshop. Five minutes is long enough to capture some movement in the stars, and as long as the gap between exposures isn’t too long it should be possible to get continuous trails. Unfortunately none of those experiments quite came off, but I’ve learnt some useful lessons.

Finally I decided to go for a really long exposure – almost 25 minutes (I was aiming for half an hour, but it was cold and I wanted to go to bed!). As expected the sky was getting really bright from the ambient street lighting and the sensor noise was building up. Still, with a little judicious tweaking of levels it was possible to see the stars rotating around the pole star (neither of these work well at thumbnail size, just click for a larger version).

For an experiment it worked out reasonably well, and I now have a better idea of what to do if I can find the combination of a clear night, no moon and darker skies a little further away from civilisation.