post color correction to optimize the M8 files

[mwalker649]

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On the "mothership" thread some of you where discussing post process color correction to get the most out of your M8 files. Can you go into depth on this, are you talking about camera calibration or special profiling for lens?

[garyvot]

On the "mothership" thread some of you where discussing post process color correction to get the most out of your M8 files. Can you go into depth on this, are you talking about camera calibration or special profiling for lens?

 

Mike, I have not read the other thread, but I assume you are referring to the "UI/IR magenta/cynan" color correction... There are several diifferent but related issues:

 

1) Because RF cameras lack a mirror, wide angle lenses can be built without resort to retrofocus designs, which means they rear elements are much closeer to the sensor (or film plane). This causes light reaching peripheral areas of the sensor to have a much higher angle of incidence than light striking the center portion, leading to difficult problems of vignetting that have only recently been (partially) overcome in sensor design. These effects can be corrected for in-camera or in post-processing if the lens type and focal length are known. Hence, the new Leica 6-bit lens coding, which tells the camera about the lens in use.

 

2a) In part because of the constraints on sensor design imposed by the first problem, the Leica M8 sensor (made by Kodak) has a very thin infrared filter that does not quite block all infrared light. This can cause magenta shifts in dark synthetic fabrics under incandescent light, for example. The solution is to use an IR-blocking filter over the lens for most photographs (you can think of it as being equivalent to a UV "protect" filter, albeit a more expensive one).

 

2b) However, the use of IR-blocking filters leads to a new problem: cyan color shifts towards the edges of the frame, particularly with wide-angle lenses. This too can be be corrected for in-camera or in post processing if the properties of the IR filter and lens type and focal length are known.

 

Updated M8 firmware can correct everthing in-camera but assumes the use of Leica-branded lenses and filters. Alternatively, you can use post-processing software called CornerFix, developed as a wonderful community service by Forum member Sandy McGuffog.

 

With the newest firmware, if you already own coded Leica-brand lenses and use Leica's IR filters, then the M8 "just works". With other brands you can still rely on the firmware to simplify your workflow, but your results may be slightly off depending on which brand of lens and IR filter you use.

 

On the other hand, CornerFix allows you to profile any lens/filter combination so that color shifts and vignetting can be completely corrected. However, there is more work to do and time lost in post... If using CornerFix, you can turn off the lens detection / IR filter processing in camera via a menu setting on the M8.

 

Hope this helps.

 

Gary