Can someone explain what microcontrast means?

[Herman Zhang]

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Con someone explain to me what microcontrast means please?

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[Danner]

Here's description I copied from fredmiranda(dot)com, posted by a user named Philip

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The definitions are an issue, particularly in the present day when thinking something often makes it true in the mind of the thinker. You can always use the terminology the way the inventors of MTF intended, however.

It's actually a thorny area, with a lot of nuanced issues that in many cases are hotly contested. Fortunately it doesn't really matter any more as most all new 'real camera' lenses produce excellent microcontrast. The basic history is that, before MTF, designers strived for high resolution with little attention paid to lens contrast levels, with poor results - until Carl Zeiss engineers conceived and developed the notion of the modulation transfer function, or MTF, around the 1950s.  

They argued that the best real world metric of lens technical performance could be gained by measuring and recording lenses' ability to distinguish ever finer elements of black and white content, then using carefully chosen spatial frequencies in that process to end up with our familiar MTF charts. Representative orientations of concentric and radiating lines described the points of recording, producing our cross-frame patterns.

Might help:

"Incidentally, it is not the case that, when designing a lens, a decision has to be made between high resolving power and good contrast rendition; both are possible for lenses with good correction.

But what does ‘contrast rendition’ actually mean? We must not forget that when we talk about ‘contrast’ we always mean micro-contrast, i.e. structures, which we can just about see or just cannot see with the naked eye, for example on a slide. But if we photograph a chessboard, for
example, so that it fills the format, the contrast between the black and the white squares has nothing to do with this. 

MTF measurements say nothing about this macro contrast. They gauge only the correction of the lens, i.e. the small deviations of the light beams, while the macro contrast depends on the veiling glare of the lens, i.e. on the large deviations. These result from undesirable reflections between the optical surfaces and from light scattering at the interior barrel components, so that they usually reach the image plane a long way from the original target. [stray light is now design enemy #1]

All these characteristics are often mixed up with each other in the term ‘brilliance of the image’. Good MTF values at low spatial frequencies are necessary, but they are no guarantee for brilliant images."

- Dr Hubert Nasse (Carl Zeiss)

So, microcontrast always refers to structures in the image which we can just barely see or just cannot see with the naked eye. The lens's performance is best judged by its overall depiction of very fine image content. You may want to think of the 'fine detail' line pair of 40 lpmm (or more) as a summary measure, but remember the lens performance is the sum total of all spatial frequencies, for example the broad edge of a person's cheek in an image is in scope just as much as their skin pores. 

It is an extensive subject, one that moves into the psychology of perception, as hinted at by Nasse. Content that we 'just cannot see with the naked eye' is at the core of MTF, and this is pure visual perception - data that is at the limit / beyond what can be seen, that is intuited as much as it is 'seen'. Hence 'micro'.  

[spydrxx]

Before you get into the nuances of microcontrast it may be useful to view this chart:

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[adan]

Microcontrast is more or less what the name says - a characteristic of a lens that maintains control of the tonal contrast in the smallest (micro) details in an image. As opposed to the overall picture contrast.

A lens with high microcontrast can produce an image with the appearance of resolution that may not actually be there, by maximizing the clarity of tonal distinctions (light, dark, in between) at edges and in textures, rather than their actual resolution in lines-per-mm.

Attached is a photo (with detail crops) of my favorite "micro-contrast" test subject, since it is permanently parked across the parking lot at my local camera store. And contains lots of tiny black-on-black and silver-on-silver details. (Plus, it's always smiling at me. 😉)

The image was made with a Leica M10 camera, and the 90mm f/4 Leitz Elmar-C from the early 1970s. 

As we can see in the cropped details, that lens is not perfectly sharp down to the pixel-level, at f/4. Nor does it have especially high overall contrast (nothing in the picture extends to pure black or pure white).

Nevertheless it has good microcontrast - tonal definition of fine details that makes them stand out from their surroundings. Even when they are black-on-black paint chips, or gray-on-gray grass blades.

Or a single-color silver hood-latch - in which we can still see all the planes and angles of its 3D form, as distinct and different grays.

Or screws, where the lens clearly retains the impression of the +-shaped Phillips indentations.

They do not become a "mush" of similar grays.

As Danner reports, this was "discovered" by Zeiss, in research where they found out that modest-resolution pictures (~40 line pairs/mm) with high microcontrast "looked sharper and clearer" to test-observers than did images with higher actual resolution, but lower microcontrast. That knowledge was no doubt used by Leitz in designing the 90 Elmar-C a decade later.

Digital sharpening is basically an attempt to replicate the effect of natural lens microcontrast with a numerical algorithn (to one extent or another). Increase the apparent micro-contrast (a.k.a clarity-definition-acutance) within and along the edges of small details. Whether they are actually sharp or not.

See also the painting technique of chiarscuro ("light and shadow"): https://en.wikipedia.org/wiki/Chiaroscuro

Details full-resolution

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Whole image larger

 

[250swb]

Putting manufacturer names to higher/lower micro contrast the Contax G1/G2 rangefinder camera lenses have high micro contrast and the image 'pops', but Leica rangefinder lenses have less micro contrast but are sharper. Obviously there are exceptions especially in the much wider Leica range, but you get used to the lens you have.

[UliWer]

vor 6 Stunden schrieb spydrxx:

Before you get into the nuances of microcontrast it may be useful to view this chart:

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Simply register for free here – We are always happy to welcome new members!

If you keep this chart in mind you will find out that "sharpness", "resolution" and "micro-contrast" describe the same thing by looking at different factors:

Imagine the black (or grey) and white lines not as "fat" as on this chart but just e.g. 40 pairs of black (or grey) and white on one millimeter:

The blurred edges of the example in the upper right will make disappear the distinction between black and white: you'll just see dark gray. The lack of color contrast for forty pairs of light grey and white in the example on the lower left will also make the distinction disappear: you'll just see bright grey. So there is no micro-contrast without sharpness and also no resolution without micro-contrast.

Though on the lower left example you have a chance to gain something by postproduction: pull down the shades in midtones, increase the lights, increase contrast further and you'll have a chance to achieve better resolution - though you'll loose the lenses "character" and better use one which has more overall contrast. 

   

[evikne]

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Some images have a texture that I can best compare to “frosted glass”. They are crisp and seem to have a myriad of details (this can of course seem contradictory as frosted glass is supposed to make things blurry). I've seen it both from some modern APO lenses, but also from some older designs when stopped down. Only the modern lenses can exhibit this also in the bokeh when wide open.

I don't know if this is due to micro contrast, but I really like it when I see it.

Edited May 7, 2024 by evikne

[pgk]

Microcontrast is quite simply the ability of fine detail to be perceived in an image.

Technically it is more complex because it is dependant on the contrast of the fine detail in a scene and its 'translation' into the final image. So very high microcontrast is easy to appreciate if it is well translated into an image, but as the contrast of fine detail diminishes in a scene it will become more dfficult to see such detail in a final image. If you look at MTF graphs these give an idea of how the contrast reduces as detail becomes finer. If we can no longer distinguis contrast then the detail has gone and a 'rule of thumb' is that 10% MTF is the cut off of what we can see. So an MTF graph based on 100% contrast in a scene will no longer resolve fine detail as the graph hits 10%, but if the fine detail in a scene is not 100% contrast (as it rarely is) in the scene (as in; not black and white and well illuminated) then it will not be resolved as well or may not be resolved at all. So microcontrast is dependant on lighting and fine detail tonality in a scene as well as the ability of a lens to image it.

Simple example from the other evening. The fine detail of the grass is well resolved where it is well lit but disappears where it is shaded.

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Edited May 7, 2024 by pgk

[thighslapper]

12 hours ago, Herman Zhang said:

Con someone explain to me what microcontrast means please?

I've always regarded it as a term in search of a definition and rather cynically assumed it was coined either in desperation or as marketing hype in place of trying to explain the nuances of an MTF graph.  

Perceived sharpness depends on contrast and that depends on the resolving abilities of the lens. Not sure where the micro bit enters into the equation. 

[pgk]

1 hour ago, thighslapper said:

Not sure where the micro bit enters into the equation. 

It refers to contrast at High Spatial Frequencies .....

[adan]

2 hours ago, thighslapper said:

Perceived sharpness depends on contrast and that depends on the resolving abilities of the lens. Not sure where the micro bit enters into the equation. 

Not quite that simple. Although it's certainly true that approaching zero resolution, contrast become irrelevant.

Remember that when Zeiss did its research, there was no such thing as pixel-peeping. Zeiss was showing its test-observers prints from film, likely at a manageable size (maybe even some "drugstore" consumer prints of 4x6 inches/10x15 cm - which would have covered about 99.9% of non-technical consumer/enthusiast photography). Or possibly some projected slides - wall-sized but farther away.

Even today, we don't usually see most pictures "full resolution" (pgk's "Moor" example above, larger on our screens than most consumer prints, is 2.2 megapixels on screen (1800 x 1200 pixels)).

Assuming it was originally made with a 24x36mm sensor or piece of film, his camera lens would only have needed to resolve a dismal 25 lpmm - any detail finer than that would have been "lost in translation" and imperceptible, even with a magnifying glass.

But the full contrast is retained, so that the "low"-resolution grass blades still pop out, and appear sharp ("Sharp," like MTF, is ALL about perception and appearance).

Last night, I made this variation on spyderxx's diagram, to show how lens engineers applied Zeiss's findings to get more perceptible contrast and clarity, even with lower resolution. By controlling the "point-spread/line-spread function." But it is applicable here also.

https://en.wikipedia.org/wiki/Point_spread_function

In the upper section, a lens is resolving (as we can see) a line pair. But at low contrast, due to aberrations spreading out the total light energy around the distinct lines.

In the lower section, the hypothetical lens resolves less (one fat line), but the lens engineer keeps all the light energy "corraled" in a tighter space, with less spread. By better-correcting and balancing the aberrations (spherical, astigmatism, coma) rather than chasing resolution per se. A technique made available by the then-recently-introduced computerized lens calculations.

Step back from the screen 4 meters/13 feet - to simulate viewing a complete image at a reasonable size - and then see which version produces a more distinct and apparently-sharp line, or "detail."

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