My take on the aerochrome problem

[Chris Barne]

I've been experimenting on aerochrome emulation for the last 8-9 months using a lot of information from all over the web (a lot of which I found on here).

 

The main thing that I have found is that in order to get very distinct variations in foliage, the amount of incoming infrared light needs to be cut. It seems as though pretty much every species of tree and plant reflects the same amount of infrared (which makes sense as chlorophyll a is highly conserved between all land plant species).

 

To this end, the triple bandpass 550/660/850 from MidOpt is attached to the rear of my lens and the HOYA X1 to the front. This leaves me with images that are extremely green, but have the correct amount of red and IR light for a successful conversion.

 

My workflow then generally involves desaturating the greens in lightroom and then performing the standard channel swap in Photoshop. 

 

Even with somewhere between -60 and -80 saturation applied to the greens in lightroom there's is still plenty of colour left to give the deep blue sky with white fluffy clouds that I'm after so much, without having to worry about the magenta cast that I've seen mentioned before.

 

I'll keep iterating through, and I have seen Fandy's post about using a linear colour space so I may try that out on some existing files. 

 

I also need to try out a circular polariser to see if I can get the sharp drop off in the skies that I've also seen from some film photos.

[Andy Perrin]

2 hours ago, Chris Barne said:

It seems as though pretty much every species of tree and plant reflects the same amount of infrared (which makes sense as chlorophyll a is highly conserved between all land plant species).

The first part of the statement is mostly correct, but the proposed explanation is not. The Wood Effect (named for physicist Robert Wood, not because it’s seen in the woods…) is caused because chlorophyll is transparent in IR so the light passes through it and is scattered efficiently by the material behind it, very much like snow scatters white light. 
 

Re “every species reflects about the same amount of IR”: Evergreens seem to reflect less IR than deciduous trees. But I mostly agree with that comment.

[Chris Barne]

36 minutes ago, Andy Perrin said:

The first part of the statement is mostly correct, but the proposed explanation is not. The Wood Effect (named for physicist Robert Wood, not because it’s seen in the woods…) is caused because chlorophyll is transparent in IR so the light passes through it and is scattered efficiently by the material behind it, very much like snow scatters white light. 
 

Re “every species reflects about the same amount of IR”: Evergreens seem to reflect less IR than deciduous trees. But I mostly agree with that comment.

Yes, you're absolutely right I got it backwards - infrared light is reflecting off the internal structures of the leaves and not the chlorophyll. Would have thought I'd studied photosynthesis enough to remember that it's blue and red light that is absorbed. Oh well...

 

Thank you for the correction. 

[Lou Jost]

12 hours ago, Chris Barne said:

Yes, you're absolutely right I got it backwards - infrared light is reflecting off the internal structures of the leaves and not the chlorophyll. Would have thought I'd studied photosynthesis enough to remember that it's blue and red light that is absorbed. Oh well...

 

Thank you for the correction. 

However, chlorophyll does emit IR as fluorescence in natural light. This would of course be much weaker than the reflected light though.