Thursday, June 20, 2013

Infrared--RT's simple workflow.

I've never been that wild about taking infrared images. Not because I don't enjoy looking at them. Rather it because I spent multiple years of my working life designing, building and servicing unusual and very expensive infrared instruments. Learning the ins and outs of IR photography wasn't going to teach me anything I didn't already know.

So I was more interested in seeing how flickr's new interface worked when I happened to visit the discussion area in flickr's Digital Infrared group three day ago.  The thread that caught my eye was on Lightroom, infrared images and some over complicated problems you face using that editor.  I was about to jump into the discussion and shout out all the ways RawTherapee works better, when I thought it wouldn't hurt to process an IR image to check that I knew what I was taking about.

After searching around in my backup folders-- I had vaguely remembered taking a infrared set three or four years ago--I found these images.  And yes, the much simpler RT workflow that produced these little masterpieces is worth blogging and bragging about.

My IR camera is a digital antique, a 3.2 MP Olympus 3020Z, the first digital camera I owned. It has, by today's standards, a weak IR blocking filter. When combined with a Hoya R72 filter it takes a decently exposed sunny day image using shutter speeds of 1/8 of a second.

I must have used a tripod when I took this in 2011. But while preparing for this post I discovered I could loop my camera strap around my neck and use my two legs and my monopod/walking stick to create an impromptu tripod stable enough for shake-free IR images. Big advantage. I'm a handheld photographer.  I'm not interested in lugging a tripod around when I'm out hiking with a camera.

Now the workflow using 64 bit RT

Although I didn't highlight it, up at the top you can see this is a tif file. Without any post processing it loads up with  a perfect 'white balance.'  This is caused by the camera's unusual sensor, one that uses a yellow, cyan, magenta demosaicing filter instead of the standard Bayer red, green, blue filter.

During the camera's internal calculations to create an RGB image that can be displayed on normal monitors several things happen.

1-The camera creates identical RGB channels from the internal IR RAW values. This is an excellent starting point for B&W images and a no-go for any false color IR images. For those I'm going to have to use a different camera.

2-The blue sky noise is half of what one would expect using a RGB demosaicing filter. At the time this was a marketing tool. I remember one salesman holding up a 30in print of mostly blue sky to promote the noise figure of the camera his store was pushing that month.  He also ignored me or didn't understand me when I pointed out some of the technical reasons his big print didn't prove anything.

3-The biggest and most not technical reason was that in normally printed,  real world images blue sky doesn't need  noise reduction. My 3020Z has low noise highlights coupled with high noise shadows with about twice the noise of a similar RGB camera.. Why? There is a signal averaging step in the calculations which degrades the low signal results when making this type of comparison.

As for the TIF file--whatever version of RT I was using 3 years ago didn't do jpgs. So I was stuck with oversized tifs, 7 images only in the 128MB memory cards that were considered huge storage back when I bought the camera.

From the history pane, I played around with the noise reduction before I did any sharpening. You can do the same thing in two steps by switching to a default ISO noise profile and tweeking the exposure slider. With no sharpening and RT's noise reduction there is no visible noise in the black sky even when displayed 400%

While I've brought up a trace of noise with sharpening , look at the detail in the trees full size to see what I've done to improve the overall image.

With a camera this old it's not surprising to find a hot pixel that require a trip to GIMP.

The clone stamp tool fixed that problem.

 Once again here is what I loaded into my flickr account. In the last two day it has gotten a decent number of views, comments and favorites from other IR photographers.

This is an image I took yesterday-one not as visually interesting but taken only a few steps away from my front door.  It is the street entrance to the greenway that  loops around behind my back yard and leads to Pilgrim park.  Long time viewers of my flickr account might remember the nature walks with young Charlotte that always seem to end at the slides and swing sets there.

With this I tried a different sharpening tool-Contrast by Detail. Notice that I dragged the first slider back to reduce single pixel noise.

While this is out of order and happened before the sharpening,  I found the line of trees a bit boring and added an artifical vignette,

For one final editing step I flipped the image.  The jury is still out on the question 'improved composition?' What do you think?


 To download RawTherapee 4,0.11.1

An up to date english  manual come with the download package. You can also find it plus non english language manuals that arrives as RT volunteers translate them at:


  1. Would that be Charlotte Johnson :-D

  2. Honestly I am confused by the post. While the title is IR workflow, the images produced by the camera are not modified in any way by RT to produce the IR effect. The poster seems to be interested in fishing for compliments on his photos. A complete waste of electrons and magnetized ferric oxide IMHO.