Tuesday, 9 July 2019

Solar panels and 'reflective' grass

I was interested to read in today's Guardian that BP are researching the most reflective kinds of grass to plant underneath solar panels; panels that pick up on top and underneath. The story points out that "bifacial panels can increase electricity output by almost 15% – but this can be much higher if the ground beneath the panel is particularly reflective".

Although the story doesn't mention it, regular readers and fans of infrared photography will know that grass (as well as other foliage) strongly reflects near-infrared light due to the retro-reflective effect of those wavelengths travelling through plant cells. Chlorophyl is transparent to near-infrared radiation. The effect is the same one that makes snow appear white, which is why infrared photos and snowy scenes can be confused.

The Solarquotes blog in 2017 looked at the proportion of solar radiation that a solar panel can exploit. Their context was about UV but if you scroll down the page you'll see a diagram that shows that a silicon solar panel will make use of radiation between 400 and 1100 nanometres. Since visible light extends from about 400 nm to about 650 nm you can see that including near-infrared more than doubles the available energy.


All this makes planting grass underneath bi-directional solar cells a logical thing to do. That reflective grass is not just fun for infrared photography then ... or grazing!

Tuesday, 18 June 2019

Infrared astronomy faces a gap

In late 2016 I noted that the James Web infrared space telescope was two years away (in this post) but it now seems that the launch has been pushed back to March 2021 at the earliest. This delay means that there will be a gap in infrared observation capabilities, as the Spitzer is set to cease operation over a year before that.

More information on this can be found on the Scientific American web site.

Friday, 24 May 2019

Photocrowd IR competition

Occasionally photo communities ask for, and sometimes rate, infrared photographs. DP Review have done it in the past and I selected one of their winners for the 2010 Infrared 100 exhibition.

Just launched is one for Photocrowd. If you're a member, or want to join, you can submit photos and rate others. In this case the contest finishes on the 28th. Anyone can view the entries. The ones so far include some interesting ones as well as some strange ones, some of which are (IMHO) not even infrared images! But worth a peruse.

Go to www.photocrowd.com/photo-competitions/infrared-1-technique-photo-contest-5980/.

Wednesday, 13 March 2019

Injections can give you near-infrared vision

Scientists in China and the USA have developed a technique to extend the range of vision by injecting nanoparticles behind the retina (so without any external technology). These particles bind to the photoreceptors in the eye and can convert low energy (near-infrared) photons to a higher energy (green). This has been demonstrated to allow mice to add near-infrared to their range of visible 'colours' with no side-effects.

I first came across this in New Scientist: Mice given ‘night vision’ by injecting nanoparticles into their eyes ... but the full paper is also available online via Cell.com.

One interesting thing about this is that a transfer of energy also occurs in photosynthesis, between types of chlorophyl) and in sensitising film to accept longer-wavelengths.

[Ma et al., Mammalian Near-Infrared Image Vision through Injectable and Self-Powered Retinal Nanoanten- nae, Cell (2019), https://doi.org/10.1016/j.cell.2019.01.038]

Monday, 25 February 2019

Presentation at RPS Bristol April 13th


I have arranged to give a talk about infrared photography at the amazing new RPS building in Bristol. It will be at 1400 on Saturday April 13th, lasting about an hour and a half.

The RPS are at: RPS House, 337 Paintworks, Bath Road, Bristol, BS4 3AR

More info here: rps.org/events

Tickets are £10 (£8 for RPS members) and £6 for concessions.

I hope to see you there.

Monday, 11 February 2019

What ... no comments

Sorry, but I have decided to remove the comments facility. For the past year or so almost every comment posted has been spam, presumably designed to help someone else's SEO, and not adding anything to what I have written.

Monday, 28 January 2019

What colour is the sky in your infrared world?

If you take a digital photograph using a camera which has no infrared-blocking filter, infrared will pass through the colour-filters (the Beyer matrix) on the sensor and will register with the red, green and blue photo sites. With an infrared filter such as the common 720nm one, almost all the radiation reaching the sensor will be invisible to the naked eye. (Saying a filter has a wavelength of 720nm means that at 720mn the filter blocks 50% of the light with shorter wavelengths reduced more and longer ones by less.)

The three colour filters on the sensor will pass near infrared light but in differing amounts and that results in what seems to be a colour picture. I call this faux-colour to distinguish it from the false colour that infrared Ektachrome produced.

It will usually look something like this ...


Here the colour balance has been adjusted slightly to make the foliage appear white/grey but even without this change the sky is a reddish-brown colour.

If you don't like this you can change it since there is no correct version of this colour arrangement, it is purely an artefact of your camera's Beyer filtering when confronted with near-infrared.

The usual technique is to use the colour mixer in Photoshop (or similar) to swap the red and blue channels which results in this ...


There is an alternative way, which is quicker and produces slightly different results. If you convert the image from RGB into LAB colour then you can invert (make negative) the A and B channels to change that reddish sky to a blueish one. Neither of the A or B channels has a red-blue axis. Red-green (A) and yellow-blue (B) are the axes of the components: colours are defined by their position along those two axes (and the L is the luminance or brightness).

Inverting the B channel changes the sky to a blue colour ...


This is different to the channel swap result. Inverting the A channel has a much smaller effect on the image but you can do this as well as inverting B to get this result ...


So now we have three ways to post-process the faux-colour images. My personal preference is for the one with both LAB colour components inverted, but your mileage may differ.

Thursday, 10 January 2019

Trees and the Wood effect

The effect in infrared photographs where foliage appears bright or white is known as the Wood effect. This is named after Professor Robert Williams Wood rather than wood as in trees. What happens is that light around in the high 600 nanometres wavelength is not absorbed or reflected by chlorophyl. So the light bounces around inside plant cells and either passes through or comes out, including towards the viewer. This happens with snow, which is why infrared and snow scenes are sometimes mistaken for each other.

The amount of Wood effect isn't related to the colour of the leaves, as these two photographs show. First a pair of trees, of definitely different colour ...


When you look at the same trees through a 720 nm filter you can see that they look basically the same ...


Incidentally, the Wood effect happens in very deep red, rather than in true near-infrared. You can prove this if you have a 720nm filter. Go outside on a sunny day and look through the filter at some foliage. It will be very faint, but you will see the glow.