Lomo Purple inspired IR style

You may or may not be familiar with the film stock "Lomochrome Purple". It it's a special emulsion created by the company Lomography. Some have said it is designed to replicate Aerochrome but without the need to capture infrared light. in my opinion It's something completely different and calling it an Aerochrome substitution film is very misleading.

On a technical level it is a negative film that makes what we would call in digital photography a Blue/Green channel swap. It's as simple as that ! In theory it's very easy to reproduce in digital format.

In practice however you don't always get the same hues when channel swapping digital visible images in your software of choice.

What I did then was to find a way to prep my digital images for the B/G channel swap with filtration on my full spectrum camera.

Here are the results : a four filter stack + a B/G channel swap

I noticed that the Lomochrome purple film had green undertones in the shadows so I had the idea to use a very small quantity of IR to color the shadows.

In these images visible green is represented as blue, red stays red and IR appears green.

That is the filtration I used to produce these images :

Each filters has a function :

• The yellow filter is there to push the white balance towards the blue which in turn influences the color of the IR (it makes IR appear blue). It also serves as a way to makes the sky teal which prevents the blue sky from turning into green after the B/G channel swap, It will just stays teal. 

• The DB830 is there to reduce IR and only let the bluer part of the IR in

• The GRB3 reduces drastically the amount of IR coming in, leaving them at the state of scarps.

• The didymium filter makes the SOOC greens more green and cuts all yellows that would go too magenta after the B/G channel swap. That helps preserving straw tones a little bit.

That's what a SOOC image looks like, The colors are close to normal but you can see slight blue undertones in the depths of the foliage :