Sigma "Merrill" micro-contrast

Micro-contrast exposed:

There are still many discussions about the pronounced micro-contrast of the Sigma "Merrill"cameras.
Some love it, others criticize it and prefer the softer look of the "Quattro" generation.
There are claims that, because of the harsh look, the "Merrills" are not good for portraits but better for landscapes etc.

The fact is: It's your decision if you want the image to be harsh or smooth. It's all "hidden"
in Sigma Photo Pro.

There are three main settings that affect the micro-contrast of the image:

• SPP chroma noise reduction
• SPP monochrom mode
• exposure (before taking the image, not within SPP)

 1. Chroma noise reduction:

Less chroma noise reduction produces less micro-contrast
More chroma noise reduction produces more micro-contrast

2. Monochrom mode:

Using SPP monochrom mode produces less micro-contrast.
Yes you lose the color, but the solution is simple:
1. convert a color version of your image
2. convert a monochrome version of your image
3. Open both images in Photoshop as layers, put the monochrom image on top
and set the blending mode to "luminance"
Now you have the colors of the color image and the luminance information of the
smoother monochrome image.

3. Exposure:
More exposure while taking the shot results in less micro-contrast.
More exposure/light "fills" each pixel with more data/color information, thus,
Sigma Photo Pro doesn't need to apply its micro-contrast generating chroma noise reduction.

Lets have a look what this means in a real world sample:

Here is an "underexposed" and an "overexposed" photograph of the same scene.
(bracketing on a tripod)

Lets bring them to the same brightness in Sigma Photo Pro:

They look similar now. Now let's take a closer look at the ancient door:

Clearly visible that the lesser exposed image on the left has less color and stronger micro-contrast.

Chroma noise reduction

Let's apply more and less chroma noise reduction to the lesser exposed image.

Again quite clearly, more chroma noise reduction (+2) leads to more micro-contrast 

SPP monochrom mode
The same image (1/6s exposure) on the left with a SPP monochrom conversion as luminance layer.
Result: less micro contrast

And finally the two extreme samples side by side
Left: more exposure and monochrome
Right: less exposure plus maximum chroma noise reduction

Conclusion:
These different methods can be used, tweaked and combined to get exactly the look you want.
Sigma gave us, presumably unintentional, a very powerful tool with the Merrills and Sigma Photo Pro. It's almost as if you have different cameras in one device.
Unfortunately, all the described options are gone with the Quattro generation.