Sunday, 3 July 2011

Software correction to the PL45?

One important aspect of the Micro Four Thirds system is the software correction to the images. Traditionally, lenses need to correct the images optically, so that the medium capturing the images sees the correct image. With the advent of digital imaging, though, the camera can do software based corrections to the image, adjusting for aspects that the lens does not correct.

This has the potential of making the lenses smaller and cheaper. Also, by allowing some aspects of the lens output to be adjusted with image processing, other aspects not possible to correct with software can be given more weight in the design process. This has the potential to give a better image quality. I think that software correction of lens output is a good thing, however, it remains a controversial issue.

One aspect which is corrected with a number of Micro Four Thirds lenses is geometrical distortion. I have explored this in a number of articles, here is one summarizing the effect for a number of lenses.

The other aspect corrected with some lenses, is some chromatic abberations. In my study, some chromatic abberations are corrected for lenses like the Lumix 8mm fisheye, the Lumix 20mm pancake and so on. Currently, this correction is only done when using Panasonic Micro Four Thirds cameras. At the time of writing, Olympus cameras do not perform the CA corrections.

Panasonic Leica 45mm f/2.8 macro

There is some rumor on the internet that Leica branded lenses are not corrected using software. This is clearly not true, since a number of Panasonic compact cameras feature Leica branded lenses that are corrected for geometric distortion. Examples include the Lumix LX3, and Lumix LX5, as well as the Leica branded counterparts.


But what about Leica branded interchangeable lenses? The Panasonic Leica 45mm f/2.8 macro lens (PL45) is the first Leica branded Micro Four Thirds lens. Are there any software based adjustments to the image output? Let's try to find out.

Geometric distortion correction

Here is an example image taken with the Panasonic Leica 45mm f/2.8 at f/2.8:


By looking at the uncorrected RAW, and comparing with the out of camera JPEG, we can easily see if there was any geometric distortion correction. Here are 100% crops from the lower left corner:


As we can see, they are identical in terms of geometric distortion. The RAW image contains about eight more pixels along the borders, which is why a bit more detail is visible from the wall and the leaves. I have previously written about this: Using RAW gives you approximately 1% more megapixels.

Corrections of Chromatic Abberations

So we conclude that there is no geometric distortions correction when using the PL45 lens. What about CA corrections? Usually, we see the CA artifacts most easily in the corners of the image frame, and where there is a huge contrast between light and dark elements. A typical place where this is visible, is where foliage meets the sky. So let's try to see in the upper right corner:


The exposure and white balance is not entirely the same in both crops, so it's not straight forward to compare them. But I think it is safe to conclude that there is no more or less CA artifacts in either image, thus indicating that there is no in camera CA correction performed for this lens.

In my previous study of some Panasonic lenses, it was easy to see that there was a correction of some CA artifacts.

Conclusion

Based on my study, I conclude that there is no software correction of the image when using the Panasonic Leica 45mm f/2.8 lens on Panasonic cameras.

This does not necessarily mean that no Leica branded Micro Four Thirds lenses will feature in camera adjustments to the output image. There is a newer Leica branded Panasonic Lumix 25mm f/1.4 lens. I have not tried it, and so I cannot say if it features this kind of image processing or not.

Note that this is in no way a criticism of using RAW images. There are many RAW image converters which will do the distortion correction automatically and seamlessly, and you will never notice that there was any geometric adjustment done at all. I am using the RAW images to visualize the initial image captured by the sensor, as it is the only way to access it.

2 comments:

  1. Have You tested Intelligent Resolution feature of GH2?
    I'm interested in what you think about it.


    PS
    I've recently purchased Panasonic Leica 45 mm macro elmarit... very nice lens indeed. Thanks for your effort, I value information you provide here.

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  2. I haven't tested the various resolution and sharpness features of the GH2. From what I've read, they work quite well. But I haven't done any systematic test of them.

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