LED Road Test - Selfie Phenomenon - Blog 9 Nov 29

29 Nov 2015

The selfie phenomenon has gone completely viral, it is probably the most common type of photograph taken today. This blog will explore a little bit how LEDs might play a role in this ubiquitous phenomenon and a little more generally how LEDs affect photography.

There are vast numbers of ways to use LEDs in photography and the BLE LED module from Texas Instruments enables a tremendous range of experimentation. This blog can only hope to cover a small fraction of the possibilities.

LEDs are available in many colours but they all emit a range of colours around their nominal colour as illustrated in this spectral plot:

If you combine red green and blue LEDs the light appears white, but if that light shines on a surface that only reflects yellow, the surface will appear dark because there is actually no yellow light in the the white light obtained from RGB LEDs.

Even white LEDs (which all use a white phosphor driven by a blue LED) don't emit a uniform range of colours as shown in this spectral plot:

The situation becomes even more complicated when capturing digital photographs because camera sensors only capture light intensity (black and white) (except for Foveon technology which is only used in Sigma cameras). This means the camera must have red, green and blue filters in front of appropriate pixels to capture colours. These filters are not monochromatic either and each one must let a range of colours through. Here are some typical filter characteristics for some pretty good cameras:

These seemingly wide filters imply that a green LED will get through both blue and red filters and a picture of the green LED will have significant red and blue content. Likewise both red and blue will get through the green filter.

Here are some pictures of our black and white cat to illustrate this colour leakage. RGB histograms are shown at the right of each picture.

Taken with a white flash:

Taken with a red LED for illumination:

Note the white fur still looks pretty white due to red light leaking into the green and blue pixels.

Here is what the image looks like with green and blue removed by post processing:

Here is the cat under green LED illumination:

Here is the cat under blue LED illumination:

The cat was not too impressed with all the crazy lighting but was a good sport about it. If she wants to commandeer my computer chair she is going to have to pay the price.

I really didn't expect the white fur to come out so white in these pictures, but that is why experimentation is useful.

Here is a patch of white fur under strictly blue LED light and the same image with red and green removed by post processing:

So if you want to know what you are going to look like under various LED lighting conditions, this TI module might come in handy. If you wear makeup, it may reflect the dominant reg, green and blue LED colours differently from expectations so you may want use a light like this to select makeup that works the way you prefer under LED lighting. Unfortunately, I do not have any makeup to experiment with.

With selfies it is a different situation ... you may want to create some special effects or unique lighting conditions to give your work some extra creative flair. Here are a few examples - some of which are very hard to recognize as me:

Some of these lighting effects are very difficult if not impossible just using photo editors and there are a huge number of possibilities, well beyond what I can imagine, so I can see this very convenient technology becoming a neat addition to one's selfie accessory arsenal. With all the hordes of people taking selfies, any little twist allows you to differentiate your work.

So chalk up a couple more nifty applications for TI's magic LED module.

The LED Road Test page is here:

http://www.element14.com/community/roadTests/1481

The Lighting Group page is here:

Lighting

Here are links to my other blog entries for this road test:

LED Road Test - Proposal - Blog 0 Jan 1, 2016

Light Emitting Diodes Road Test - Blog 1 Nov 1

LED Road Test - 3D Printed Housings - blog 2 Nov 10

LED Road Test - Dodecahedron Light Fixture Blog 3 Nov12

LED Road Test - Wearable Interactive Lights - Blog 4 - Nov 13

LED Road Test - Interactive Trophy - Blog 5 Nov 16