What is microcontrast

Discussion in 'Casual Photo Conversations' started by charcoal_happy, Mar 17, 2012.

  1. What is microcontrast exactly?
     
  2. I wouldn't know where to start, and wherever I ended, someone else would propose more. My personal view is micro contrast is the ability to capture fine detail such that a distinction exists between various tonal values. With film, where I spend most of my time refining micro contrast, three (primary) factors are most important to me in achieving micro contrast: the resolution of the lens, the capability of the film (there are many components to this one), and the processing procedure.
    That is why I've spent a good amount of time experimenting with stand development, various lenses, and various films. I am constantly looking for ways to bring out specular details from shadows and highlights. Good lenses are not hard to find (but are expensive to acquire): Leica, Zeiss, Nikon, Canon, etc. Film has gotten much better, including T-Max, Delta's, and Acros. Development has been the most lengthy journey for me, but I believe I can maximize specular details (micro-contrast---and I realize some will take exception to my lumping them together) by using a developer that exhausts linearly (temporaly), such that highlights are not over developed, and shadows are coerced into yielding more information.
    There are pitfalls in these methods. For lenses, the most obvious case to me is a lens that resolves very fine details, but produces too much contrast. Some Zeiss lenses come to mind (particularly for LF). Films can have similar problems. Development is the one area where I believe I have the most immediate control over micro contrast. Where a developer falls short, I can add or subtract chemical components to get what I need. That's not the case with film and lenses (even with filtration).
     
  3. Microcontrast=fairy dust collected on the stroke of midnight in midnight sunlight. This stuff was also used by Peter Pan and enables children to fly, as documented by Disney. It is used in the final coating stages of Zeiss optics and lenses, but that is a closely guarded proprietary secret. :)
     
  4. That's certainly a theory Ingemar.
     
  5. Contrast has generally been described by the difference between the overall deepest black and the brightest highlight of a scene that a lens can faithfully transmit, while microcontrast concerns that of two adjoining and extremely small yet potentially visible subject areas, and relates in particular to very fine details of texture that the lens can resolve. If some small detail is recorded, but the microcontrast is too low, it will show up only as a sort of image noise that will simply degrade the definition of the image. If the lens is not able to record microcontrast, little variation in film or paper exposure and development will help, although, as Michael infers I think, they are also important links in the overalll chain.
     
  6. How do you measure LP/mm for the lens and for the sensor?
     
  7. Charcoal, there are entire books devoted to optical system characterization and major sections of them are typically devoted to such measurements. Typically, a grad level course in this subject is given over two semesters and carries about 6 credit hours.
    Although you will likely receive some replies which will attempt to compress all of the theoretical background, concepts, techniques, etc. into a couple of paragraphs, if you are truly interested in this subject, I suggest you may be better served by a less superficial approach either via textbooks on optical engineering or Google "measurement of MTF". There are also many folks on the web who attempt to make such measurements on their own, but often they don't get the nuances right and hence, endless / pointless discussion follows.
    Tom M
    PS - We've already seen some of the latter in this thread, specifically, the attempt to distinguish differences in small tonal values without reference to the spatial scale on which these changes occur. If folks would understand that MTF is essentially a Fourier domain characterization of an optical system, the relation between the amplitude changes and the length scales would be much clearer. OTOH, if you aren't familiar with Fourier concepts, this is going to be hard to do.
     
  8. Charcoal, there are entire books devoted to optical system characterization and major sections of them are typically devoted to such measurements.​
    What I'm looking for is the point where a lens or sensor outresolves the other.
    LP/mm used to be common information but I don't see companies publishing these figures anymore.
    What is the native resolution of slide, 35mm film, medium format etc?
     
  9. There is no sharp dividing line. The spatial resolution of an entire optical system is, to a decent approximation, the square root of the sum of the squares of the spatial resolution of the individual components. So, even if you had a lens and sensor, "perfectly matched" with the same resolution, and then you replaced one of the components with one that has perfect resolution, the overall system resolution would only be improved by a factor of about 1.4 (ie, sqrt(2)).
    Tom M
     
  10. "What is the native resolution of slide, 35mm film, medium format etc?"
    Google {MTF kodachrome}, {MTF velvia}, etc. etc.. and you will find 44,000 hits, most of them being on-topic.
    In addition, there are hundreds of long, more general discussions of the topic. IMHO, there is little use in repeating them here.
    Tom M
     
  11. "What is the native resolution of slide, 35mm film, medium format etc?"
    Google {MTF kodachrome}, {MTF velvia}, etc. etc.. and you will find 44,000 hits, most of them being on-topic.​
    Why can't you give a straight answer? If "google" is your answer, I guess you don't have a clue.
    44 000 hits of which 99% are trash. I only need one good reply.
     
  12. Trust me that Tom Mann has a clue! There's no reason to insult those who try to help you. It's not their job to spoon-feed you the information.
    FAIW, I took a course in machine vision in graduate school, a third of which was devoted to this very topic. That's how much material you're asking people to spoon feed you in this thread.
     
  13. Hello, Charcoal -
    It's very telling that you would say that 99% of the hits that resulted from Googling {MTF kodachrome} were trash because, in fact, (a) the raw numbers that you asked for, (b) the actual MTF curves, and (c) insightful discussions about the issue of film resolution were in the 5 out of 7 of the first hits that result from the above search.
    For example, about 200 words into the very first hit after Googling {MTF kodachrome}, that website states:
    " Kodak TMX has a contrast that drops by half at 100 lp/mm".
    About 100 words into the second hit after Googling {MTF kodachrom}, that website states:
    "For the E100VS green layer, f50 = 40 line pairs/mm"
    The third hit was not relevant (it was someone's gallery). The fourth was this thread. The 5th, 6th and 7th hits also gave exactly the info you asked for, although in the 7th hit, one did have to make the extra effort of clicking on a link to get to the Kodak datasheet that contained the MTF curve for Kodachrome.
    Assuming that you actually made the effort to perform one of the searches I suggested, the only possible explanation is that you didn't understand what you were seeing, even though the information was right there in front of you.
    This is exactly why in my 1st posting in this thread (Mar 18, 2012; 04:37 p.m.) I warned you that these topics are not simple and require some study. My suggestion that you do your own Googling was because I knew this would almost certainly lead you to more in-depth discussions which would help you learn about this (and related) topics. Your obvious frustration tells everyone reading this thread that you currently have an inadequate understanding of even the most basic principles and terminology in this field AND and have little interest in improving yourself. That's your loss. It is a very interesting and useful field.
    In fact, it's so interesting and useful that I've earned a good living for my entire adult life working in this area. For the majority of the 23 years that I spent at a major government lab, I was the head of optics, lasers and spectroscopy research groups and have been a full professor of science and engineering at a major university for the past eight years.
    I truly was trying to help you get into this topic.
    Good luck,
    Tom M
     
  14. Funny, I thought the subject was contrast, or a derivative of that, microcontrast? Whence cometh LP/mm? Resolution is not just that, but you have to factor in contrast.
     
  15. What I'm looking for is the point where a lens or sensor outresolves the other.​
    Your editing software is the final determiner in finding out the significance of that. There's no way to see what your lens and camera system delivers in MTF, microcontrast or whatever you want to call it until you see how the software maps each pixel that has a different tone to the next.
    My $80 kit lens can distinguish the finest detail that can deliver the thinnest hairline thickness as long as there's enough pixels squares (my 3000x2000 pixel Pentax K100D) to provide edge contrast tonal role off in making the hair look like hair and not a hard, stair stepped/pixelated edge vector graphic.
    I can increase resolution in rendering enough microcontrast for edge tonal roll off by either getting closer to the strand of hair (macro) or getting a camera with higher resolution.
    My camera tends to render most of my images with a soft, low contrast appearance which I can fix in post. That doesn't mean that my camera and lens system didn't capture and deliver the detail to my software's demosaicing algorithms. It just reduced the degree of tonal differences between each pixel square which can be enhanced using software.
    Again, it's the software, not the hardware you should be looking at. Each camera/lens combo manufacturer has tweaked their internal algorithms to give the best look to their jpegs. Just because an image looks crappier in a third party Raw converter doesn't mean the hardware is at fault.
     
  16. The 100% crop image shows lack of microcontrast and what I pulled out of the image that the lens and sensor actually delivered.
    Did the hardware do this or did the software allow this? MTF graphs aren't going to tell you the level of work that's required under every shooting condition to bring out microcontrast. You'll have to test each camera to see what their hardware combined with their software algorithms are going to deliver requiring the least amount of fixing in post. No one can do this showing graphs and mathematical equations.
    00aASS-451717684.jpg
     
  17. ArthurP: "Funny, I thought the subject was contrast, or a derivative of that, microcontrast? Whence cometh LP/mm? Resolution is not just that, but you have to factor in contrast."
    Hi Arthur - Actually, most of my comments were in response to the OP's 2nd post, in which he asked, "How do you measure LP/mm for the lens and for the sensor?". That's one of the reasons LP/mm entered the discussion.
    However, to respond to your comment and his original question, the term, "microcontrast", is commonly used in at least two different ways, so discussions of this term often get off to a rocky start when the participants are using different definitions. The simplest definition is that contrast is a large change in brightness between different areas of an image, and microcontrast is a small change in brightness, with no reference made to the length scale over which the change in brightness occurs in either case.
    Many people, myself included, find that definition is severely lacking for a variety of reasons. First, and most importantly, it is imperative to distinguish carefully between contrast / microcontrast of just the lens, vs the contrast / microcontrast of the entire imaging chain including lens AND film or sensor AND in-camera and/or post processing, exactly as Tim pointed out. Many internet discussions of this topic and these terms do not differentiate the various factors that can be included, and confusion always results. To add further confusion, many discussions even throw issues of human perception into the mix.
    However, if we restrict the discussion to the contrast / microcontrast of the lens, by itself, many of the above issues disappear. Non-controversial definitions and good measurement techniques become available.
    Specifically, the contrast of a lens means the fractional preservation of a step function change in brightness of the target in the image formed by the lens. For example, if the target consists of a set of perfectly black and perfectly white bars, you have a target contrast of 100%. Of course, the image formed by the lens will have less contrast. The ratio of these two image contrast values IS the vertical axis of all MTF graphs, and itself is also expressed as fraction. This is also why MTF curves for lenses are sometimes called "Contrast Transfer Function" curves.
    Optical bench measurement of the brightness changes in the image formed by the lens is always done using a very sensitive, low noise, wide dynamic range detector with a very small entrance aperture. Considerable care is taken in the design / selection of the measurement equipment to ensure that its limitations (eg, dark noise, diffraction, scattering, resolution of small changes in brightness, etc.) are insignificant compared to the image degradation caused by the lens. For example, in the old days, measurement of spatial changes in image brightness was often performed using photomultiplier placed behind a precisely made narrow slit that could be mechanically scanned over the image plane.
    Of course, there are many variables that will change the contrast of bars in the image plane of the lens. These include wavelength, method of illumination of the target/subject, f-stop, magnification ratio, field curvature, distance off axis, radial vs tangential orientation of the bars (aka, sagittal vs meridional), and many others, especially the spatial frequency of the bars on the target. The convention is that the ratio of image to object contrast is usually only plotted as a function of spatial frequency, but in extensive optical testing (eg, for military imaging systems), many of the other variables are often also considered and reported.
    This finally brings us to the question of what does "microcontrast" mean when applied to just the lens in an optical imaging system. Because, by definition and choice of measurement technique, we have eliminated all film/sensor and post processing issues from the discussion, we are left with just the MTF curve for the lens under discussion. The obvious definition is that the microcontrast of a lens is nothing more than the fractional preservation of contrast at short length scales (ie, high spatial frequencies).
    Of course, a photographer is interested in the performance of his entire system, not just the lens, and so, issues such as sensor resolution, in-camera and post processing, bit depth, etc. all enter the discussion, but it is much easier to do this if each component in the system is first characterized individually. The Wikipedia article on Optical Resolution is quite good and may seem highly detailed, but it barely scratches the surface of this subject.

    HTH,
    Tom M
     
  18. Tom,
    Thanks for your explanations, which I appreciated. I assumed, probably wrongly, that the OP was talking about the lens only and so I fully agree with your following comment in that regard:
    "The obvious definition is that the microcontrast of a lens is nothing more than the fractional preservation of contrast at short length scales (ie, high spatial frequencies)."​
    Tim has also added other elements of the chain that impact on microcontrast. A good and worthwhile discussion.
    When we change the level of sharpening or saturation in our camera's firmware, are we changing only jpeg output or does that also impact on a RAW file? I understand that the information from the sensor is analogue and it is the DSP that changes it to digital, but it doesn't, by itself, alter sharpness or saturation.
     
  19. When we change the level of sharpening or saturation in our camera's firmware, are we changing only jpeg output or does that also impact on a RAW file?​
    With Raw only when using the camera manufacturer's Raw converter.
    A side note about lens MTF data. As far as I can tell from reading wikipedia articles and at least what I'm finding with my own camera is that the lens's MTF data aids the camera manufacturer's choice of aperture/shutter speed/ISO shooting in Auto/Program mode with emphasis on aperture to control diffraction and local contrast appearance at certain focal lengths that affect DOF. My camera is quite clever at riding my kit lens's aperture controlled diffraction limits whenever I zoom out to wide angles.
    I like what I get shooting at my lens's f/8 sweet spot but am surprised what with sharpness appearance in what Program mode chooses especially with my jpegs. Adobe Camera Raw usually only needs a bit of clarity and sharpness to get the same results.
    I notice in Program mode my camera chooses 1/250, f/10 (instead of my desired f/8) pointing at a somewhat dimly lit sunlit morning scene outside my window and then quickly switches to 1/50, f/5.6 panning to my brightly lit white walls of my living room both locked in at ISO 800. With both differently lit scenes the aperture changes when I zoom in and out between 18mm-55mm focal lengths.
    The camera is definitely making exposure decisions that don't make sense to me but does make for better contrast, clarity and sharpness appearance in my jpegs.
     
  20. Micro contrast, in common with terms like hyperfocal distance and especially bokeh, is a term that is latched onto by beginners and touted by various and sundry egos who have been sold a bill of goods by lens manufacturers and their minions. They squabble all day long about their importance, losing sight of the forest for the trees. Another good one is N coatings and all the magic they are supposedly responsible for. By and large, folks who have come to photography only since the digital age began some 10 years ago, really don't know much about photography from what I have read in these threads. There is hardly a lens out there today that cannot produce a darned good image, if you will just look at the entire work for a change instead of using your computer as a microscope to quibble about this and that (chroma, asigmatism, and on and on and on) that are not seen by the vast majority of your audience, if you have one. I challenge anyone to look at a group of well made prints and tell me what camera, what mp, what mb, what lens they were made with. Stop worrying about micro contrast and make photos. And remember, nobody cares about bokeh but you.
     

Share This Page