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:

Wednesday, June 5, 2013

Noisewise, Is My Camera Meeting Spec?

Noise spec? you ask.  Point to where that is printed on the camera's spec sheet, you demand.  Sorry, camera manufacturers don't  spec their noise or more accurately their signal to noise ratios. Why? Maybe it's because some of us meany pixel peepers might take the number seriously and start demanding refunds. Or, to be more charitable, it might be because accurately measuring a camera's S/N ratio takes more than a look at a computer screen?

Physics-wise, S/N ratios are complicated. Photon shot noise, addition in quadrature, Poisson  statistics--those sort of things. Complications on top of complications.

A more reasonable question would be "Is my camera as good as the camera that was used  to take the photos for the review I read on my favorite photo site? The one that convinced me to buy the camera?"

If you are lucky, yes. More likely, no. Any marketing manager worth his corner office will make sure the cameras sent to review sites were hand picked for performance. But your camera should be close or you do have the right to demand your pixel peepin' refund.

This came up in the forums recently. A new user had bought a 'bridge' camera or, as I used to call them before marketing folks invented the name, a super zoom.  Those types of cameras have little sensors since, among other things, their light weight and inexpensive super zoom lenses only make little circles of focused light. Since they also pack about 12 megapixels into their little sensor--lets say the trade offs are not favoring S/N ratios and low light performance.

Our new user picked the right place to fix his noise problems even though his expectations were originally too high. RawTherapee has great noise reduction tools but there are limitations. So a question came up. Was his camera's S/N ratio within 'spec'?

Here is the workflow I used to work out the answer by using a comparison image, RawTherapee and ImageJ

I've already posted a tutorial on how to create a noise profile in ImageJ so I won't repeat the steps here.

Imaging Resource is the place to go for your comparison images. They have created a massive data base of reference images going back to the days when a 2 megapixel camera equaled a $1000 investment. And they did things right from the start, controlling details, such as consistent lighting, needed to create reference images that highlight real differences between individual camera brands.

To download your comparison image pick your camera in the review pages, go to the sample tab and then the sample image page.

Near bottom and after a multitude of jpg images you will find Raw downloads of their multi-image test shot taken with your camera's various ISO settings. It has the Macbeth color chart we will use. I downloaded the ISO6400 version  to compare it with  the bowling alley picture I blogged about earlier.

Using the neutral profile I converted both NEFs  into jpgs before loading them into ImageJ. That conversion insures I was doing a real apples to apples experiment. If your camera doesn't take RAW files, obviously you must use jpgs but then your test image must have been taken with the same setting as the reference image for any meaningful results.

Pick the closest match you can find on your image, the wall behind Rhianna, and on the Imaging Resouces' multi image, the #4 gray scale box.  Run your profiles. Compare the graphs.

That's it. Twenty minutes time max and you know how well your camera is working. Take a few more measurement, let ImageJ do the signal averaging and you have an accurate S/N number.  Then you can brag about your new camera's performance in the forums. Or. more important, toss down a hard copy on the service desk if your camera needs fixing.

As for the new user who just posted his "Thanks" -- "You're more than welcome since your questions inspired this tutorial."

You can find RawTherapee here. The package includes an updated manual