The Definition of Microcontrast

I have been interested in the rather vague term "microcontrast" and have long sought a precise definition with numbers and stuff.

Yesterday I found an article by our Jim:

blog.kasson.com/gfx-50s/mtf50-and-microcontrast-of-fuji-35-70-gf/

... complete with numbers and a definition:

My questions are: "are other frequencies in cycles per pixel relevant to microcontrast?" and "how do other units of measure relate to micro-contrast?"

For example I have a camera which can select on-sensor 2x2 binning which gives an effective pixel pitch of 18.24 um or 27 lp/mm.

I have another camera which, with pixel-shifting, gives 80 MP which gives an effective pixel pitch of 1.68 um or 298 lp/mm.

Wondering if 0.25 cy/px or those lp/mm is a microcontrast frequency on either of those cameras? I'm hoping not - because that could bring us back to vagity.

A very interesting topic and great that you got a definition by @JimKasson for it. I've stumbled upon the term occasionally and got a feeling of what people mean, but as I'm not a very technically-minded person I never looked up any real definition... so while I unfortunately won't be able to contribute anything meaningful here, I'm very interested in any discussion on the matter.

[deleted]

Must give it a try in Wavelets at the 32px level 6 for both my cameras mentioned earlier. What degree of sharpening e.g. amount, or contrast enhancement, would give "a great microcontrast"?

I would describe that as local contrast (as against global contrast, which applies to the whole image), but not micro-contrast which is on a much shorter scale to my mind.

Having said that, I'm all in favour of local contrast enhancement as a processing tool when used judiciously.

32px USM and also Wavelets level 6 applied to an 1134x768px image ...

USM radius 32px amount 23

Wavelets size 32px double contrast

Rather that a fixed cy/px or a fixed detail size, It appears that the criteria associated with SQF a la Grainger are more relevant:

www.bobatkins.com/photography/technical/mtf/sqf1.html

That is overcooked to my mind. It's better with low contrast shots:

Original image taken on a foggy day

USM(r=30, a=0.5) local contrast enhancement

and USM(r=0.7, a=2) sharpening

Yes, overcooked to show that 32px does not suit an 1134px wide image.

I did ask "What degree of sharpening e.g. amount or contrast enhancement would give "a great microcontrast"?" No response yet although "a=0.5" seem OK on your 1600px wide stuff.

The metric chosen by Jim and Bob is MTF, not contrast. Therefore, in theory, the degree of improvement, i.e. MTF, does not depend on the contrast of your original.

MTF is a property of the lens or lens/camera system, not a property of an image. In general a higher MTF at a given frequency means higher contrast in the image at that frequency, all else equal.

It is highly dependent on the image, but I often choose a=0.2 or thereabouts. It's largely trial and error.

oops - quotes messed up - withdrawn

Tom said "It's better with low contrast shots:" I responded to that statement but didn't really know what "it's" referred to. Perhaps I should not have responded.

Out of interest, I took a review test image for the Sony a6700, the which image having a slant-edge in the middle.

I re-sampled the image to 50% and 200% with Lanczos3 and then, at constant sensor size, plotted the MTF for all three images:

Note that the MTF at 0.25 cycles/pixel is greatly different in each plot. No surprise to me and that probably means that Jim's preference for that frequency to indicate "microcontrast" is for the camera that he was testing and may not be a universal value for all cameras.

Is "micro" referring to detail size or the reciprocal thereof? Scene detail? Image detail? Sensor detail?

Or does "microcontrast" mean whatever Chuck Norris say it means?

In other words, I am now thinking that I have not discovered a definition after all - and there may not even be one ...

Yes and no. Microcontrast means contrast at high frequencies. I was try to define frequencies that are high for any given Bayer CFA camera and below Nyquist.

Thanks Jim, yes, "below Nyquist" for sure. Sorry to say that I am struggling a little with "any given Bayer CFA camera" but you know me for taking people too literally ...
... although, in another blog post on your site, you did give a range of frequencies 0.2 to 0.4 cy/px, IIRC.

Yup

Ta