Category Archives: Micro Four Thirds

Micro Four Thirds Cameras and Lens Correction

Unexpected Support

Quick update on the support position for the Panasonic GX7. Phase One won’t commit themselves on Capture One support. It looks like the DNG converter is the best Adobe are going to do. I also haven’t yet managed to track down updates for some utilities like ExifTool, although they may exist.

Then last night as an idle thought I tried the RAW processing app I have on my Galaxy Note tablet, PhotoMate. It worked first time with the GX7 images! Nice.

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What’s More Important: Hardware or Software?

Eric Clapton at the Royal Albert Hall - May 2013
Camera: Canon PowerShot S95 | Date: 17-05-2013 21:55 | Resolution: 2498 x 1405 | ISO: 800 | Exp. bias: 0 EV | Exp. Time: 1/50s | Aperture: 4.9 | Focal Length: 22.5mm | Lens: Canon EF-S 10-22mm f/3.5-4.5 USM

We live, as some of you might have noticed, in a digital age. The displacement of older technologies by digital versions has been accompanied and largely enabled by rapid, substantial advances in technology. Yet a couple of recent experiences suggest to me that we may be reaching a point in many areas where further hardware change is of less importance than improvements to the supporting software.

This has most clearly been brought home to me in respect of cameras. My older, larger, cameras and lenses work by delivering high quality optics coupled with relatively straightforward processing of the captured image from the sensor. The newer, smaller cameras make some dramatic compromises on optical accuracy, and then correct the errors in software. This works surprisingly well, but introduces the challenge that if you want to shoot in RAW format and develop the shots yourself, you need RAW processing software capable of reproducing the same, or better, corrections.

That’s been a problem for me, as the software I was using (the former Bibble, now Aftershot Pro) didn’t have adequate support for my new Panasonic GH2 and its diminutive lenses. Also new owners Corel seem to be determined to kill the software through negligence, which makes the prospect of improvements unlikely. (That’s another story, to follow…)

This week I got a bit disheartened, fearing that I was becoming “locked out” of both new cameras and fully developing my work with the GH2, and finally bit the bullet. I didn’t buy a new camera, I started evaluating alternative RAW processors. After a couple of false starts I have settled on Capture One from Phase One. The results so far are very promising: it not only corrects the distortions of my Micro Four Thirds lenses, but it delivers silky smooth output from my larger Canons at ISO 3200, and does a remarkable job of highlight recovery. The shot above was taken at ISO 800 from the back of the Royal Albert Hall with my tiny Canon S95. (BTW, Eric Clapton was excellent!)

But the big surprise has been applying Capture One to some of my older images. The following was taken on our 2007 visit to the Southwest USA, using my original Canon 350D. I was never really happy with the Bibble version, which struggled both to recover the blown highlights and to pull some usable shadow detail without excessive noise. The difference using Capture One is dramatic. It’s almost like revisiting the scene with a new camera.

Getting back to the original topic of this post, I’ve also seen the same software-led effect elsewhere. Support for a proper stylus aside, there’s not much in hardware terms between an iPad and my 10″ Galaxy Note, and some might prefer the Apple hardware. However the dramatic differences in software capabilities are a real differentiator. (See my various reports for details.)

I don’t want to belittle the impressive work of digital hardware engineers, and we’ll continue to take the benefits of further advances, but we need to recognise that the efforts of frequently unsung software engineers may be just as, or sometimes even more key to the hardware’s exploitation.

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MFT: Formula, What Formula?

In a discussion with Phil Harvey of exiftool fame, it became apparent that the first problem I have to solve in respect of Micro Four Thirds lens correction is to understand the formula, or formulae, being used to apply the correction.

Most image processing software supports geometric correction via three parameters labelled a, b and c. These are the parameters in the following formula:

Ru = scale*(Rd + a*Rd^3 + b*Rd^5 + c*Rd^7)

In this Rd is the distance of a point in the image from the centre in the distorted image, and Ru is the distance it was in the undistorted image. The model is that distortion is radially symmetric, and has the effect that concentric circles of image points move either closer to or further from the centre than they should be. This translates into the more recognisable types of distortion when straight lines in the image cut across these imaginary concentric circles.

There’s a couple of useful pictures here.

There are several variants on this formula. Wikipedia has a much more complex looking version which appears completely different, as it allows for the effects of off-centre lens elements and different profiles in different directions, but if you ignore these effects then with a little bit of factoring it boils down to exactly the same equation. Bibble, for example, switches the labels a and c, and other versions factor “scale” into the individual parameters, but the basic formula is the same.

The problem is that if this is the formula used in MFT in-camera corrections, then the data isn’t the right shape. We should just see three or maybe four fractional values, and the rest should be zeros, or maybe constants for a given lens/camera combination. While in some cases you can select values from the MFT data which work, it’s inconsistent and there’s no explanation for all the other data.

We know that MFT cameras also correct in-camera for chromatic aberrations. Maybe this could explain the other data points? The trouble is that this doesn’t work either. CA correction formulae work in one of two ways. They either provide a pair of shifts for the different colour channels (requiring two further parameters in addition to the three or four for geometric correction), or you get three sets of geometric correction parameters, one for each colour channel, as per the following taken from a DNG file using one of Raphael Rigo’s tools:

r : 1.000168 -0.128185 0.052356 -0.005116 0.000000 0.000000
g : 0.999694 -0.127995 0.052335 -0.004995 0.000000 0.000000
b : 0.999967 -0.127973 0.052642 -0.005050 0.000000 0.000000

While this might explain the number of values, you’d expect to see three sets of very similar values in the MFT data, and that doesn’t happen.

There are other ways of doing geometric correction. There are other formulae, but they don’t seem to be in common use. There’s also a non-linear approach (see again), but this would need either a series of small values with the same sign (for a cumulative curve), or a progressive sequence (for an explicit curve). Of course, there could be some sort of complex differential version, but that’s cheating!

I have to assume that the model is capable of interpretation, especially since for some lenses a simple mapping works pretty well. However, it’s clearly not as simple as we’d hoped.

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The Micro Four Thirds Lens Correction Project

Although most Micro Four Thirds (MFT) lenses are tiny,  the cameras produce great JPG files with apparently little or no geometric distortion. They do this by applying corrections in camera,  and the correction parameter data is also stored with the RAW file. Unfortunately this data is only useful if you can read it,  and most RAW processors can’t.

Although there’s no obvious reason why not,  Panasonic and Olympus have not published the specification for this data.  That leaves those of us who want to use a RAW processor other than LightRoom or SilkyPix struggling to get decent results with our MFT images.

Building on some excellent work done by “Matze”  ( Raphael Rigo ( I decided to have a go at implementing a parser in my CAQuest plug-in for Bibble/AfterShotPro. However although getting the raw data is fairly straightforward I have discovered that the algorithm is more complex than we thought,  and seems to vary from lens to lens.

I have therefore decided to open up the exercise to a “crowd-sourcing” model to try and get several eyes on the problem. As we uncover algorithms which work well for one lens or another I’ll publish them here,  and also build them into CAQuest.  Over time we may come to completely understand the complete MFT algorithm,  and our work will then be done.  Of course,  if one of the MFT partners wants to help by publishing the algorithm,  that would also be perfectly acceptable :).

The project pages are here:, with a discussion hosted at the Corel AfterShotPro forum.

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Finally, Something Smaller

Detail from the side of Shakespeare's birthplace, Stratford-on-Avon
Camera: Panasonic DMC-GH2 | Date: 27-06-2012 19:24 | ISO: 400 | Exp. bias: 0 EV | Exp. Time: 1/1300s | Aperture: 8.0 | Focal Length: 42.0mm | Lens: LUMIX G VARIO PZ 14-42/F3.5-5.6

First Impressions of the Panasonic GH2

Regular readers will know that technology miniaturisation has been on something of a negative trend chez Johnston. My most recent TV, desktop, main camera and most notably laptop purchases have all been significantly larger and heavier than their predecessors. Even my latest phone, purchased a few weeks ago, is rather larger than the previous one, although there’s no real weight penalty.

However, I’ve finally bucked the trend. Recovering from knee surgery (which limits my carrying ability), and thinking about my next holiday under the cloud of increasingly challenging airline luggage limits, I’ve taken the plunge and invested in an EVIL camera (“Electronic Viewfinder, Interchangeable Lens”:) ), in the shape of a Panasonic GH2. It’s funny how several influences came together:

  • A very good Panasonic cinema advertising campaign featuring a professional taking great shots in Yosemite, using a Panasonic G3,
  • Rave reviews of the new OM-D,
  • A growing desire on my part to get a new toy and kick-start my slightly stuck photographic activities.

I had a look at the OM-D, but it just didn’t fit my hand. Oddly the Panasonic G3, almost identical in size, felt fine, but came up short on spec. A bit of research suggested that the GH2 would be a better match for my needs – a similar package, but closer to my Canons in capability. However, what really swung it was a review by Michael “Luminous Landscape” Reichmann, a man who apparently thinks nothing of spending £10k on the latest medium format wonder, who used a GH2 as his main camera for a six-month stay in Mexico last winter. Sold!

It’s been in my hands a few days now, and so far I’m very impressed. In terms of functionality, it’s closer to my Canon 7D than anything else in my fleet. There are proper knobs and switches for all the major functions, but also a comprehensive set of custom functions and buttons (the lack of which is one of the things which would make the Canon 60D a poor replacement for my much-loved 40D). Handling will take a little getting used to, but it all makes sense and with a bit of practice should work by feel with the camera up to the eye – very much my preferred mode. The electronic viewfinder is very clear, now I’ve got it focused at a point which works for my eyes with glasses either on or off!

The camera is rich in features with some, like the ability to change the aspect ratio in camera, potentially very useful. However, it has to be said that neither Canon nor Panasonic have made any progress against my list of enhancements we really need in DSLRs. Let’s hope the next generation do better, and in the meantime I’m off to investigate the growing phenomenon of GH2 “hacking”…

Image quality is really very good. Despite the smaller sensor noise levels are similar to my Canon 7D, certainly up to ISO 1600. I haven’t played with the really high ISOs yet. Beyond that is the performance of the 14-42mm “power zoom”. This comes in a package which when switched off looks like one of Panasonic’s tiny “pancake” primes, but extends when powered up to provide a useful zoom with 28-84mm range (in 35mm equivalent terms). It’s pretty sharp throughout its range, and chromatic and geometric aberrations seem to be almost absent. This conflicts sharply with the Canon EF-S mid-range zooms: the 17-85mm suffers very bad CA, the 15-85mm has very noticeable geometric distortion for a large part of the “wide” end, and neither is very sharp at the edges of the frame. Admittedly the Canon lenses have almost twice the zoom range, but I’d much rather have a really good 15-45mm “L” zoom, if only Canon made one… 🙁

All this comes in a tiny package. The camera is just about as small as it can be and fit my hands. Powered off, it’s about 3″ deep. And the body plus standard zoom is less than 500g. That’s about 40% of the weight of the Canon 7D + 15-85mm combo, or less than that lens alone. I suspect a “three zooms plus fast prime” lens set will probably still weigh less than the 7D and standard zoom lens, and not cost much more.

Now I don’t know how reliable it will be, or how it will stand up to regular use. The current version couldn’t compete with the 7D for fast action, or in very low light, although the gap is narrowing with each generation of these new mirrorless, smaller sensor cameras. Whether there’s a case for the 550D is more questionable. Will I dump my Canons for the GH2? Not yet, but it feels like the writing may be on the wall…

Update, September 2012

The apparent excellent performance of the tiny MFT lenses is due to in-camera correction of the JPG files. The RAW data shows the geometric challenges of such lenses in their full light. If you are prepared to use either SilkyPix or Adobe LightRoom as your RAW processor, then it will automatically read the correction data and re-apply it, but this is not available to users, like me, of other RAW processors. I’m becoming slightly obsessed by this problem, and now running a project to try and get to grips with it. However, I thought it worth updating my original post with this note. If you shoot JPG, then the MFT cameras are little short of amazing. If you shoot RAW, be prepared for a bit of a challenge…

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