Mega Pixel Vs Spectrum of Light

Discussion in 'Beginner Questions' started by miss.annette_leigh_haynes, Jan 28, 2018.

  1. Some years back a former Kodak guy, Dick Dickerson, had an interesting article in Photo Technique [sp] magazine, where he simulated "grain" using an Excel spreadsheet. (Try making two columns with a random function, =RAND(), then show results on an x-y graph.) The result was shown on a 2D graph, and had a striking resemblance to "grain" patterns. (Hit the recalc button to see different patterns.) So it seems likely, or at least plausible, that what we see as film grain can be largely explained statistically as a somewhat random distribution. Real film is not limited to a single plane, so grain patterns can be much more complicated.

    A second comment relates to what we see as "grain" through a microscope. Years back, circa 1980(?) I had set up some QC procedures to verify "adequate" preset focus on a proprietary camera system. Essentially, resolution targets were photographed, and the processed film was rated via a microscope - somewhere around 50 to 100 X as I recall. I still recall initially seeing the "grain" (actually it was color neg film) and thinking that it would limit the resolved detail. Then being surprised to see that the resolved detail was much finer than what seemed possible.

    I won't try to explain except to say that anyone looking at color film "grain" under a microscope without an underlying "image" may be easily fooled as to the limiting effect on recorded detail. After this, I looked at grain as not setting a limit to fine detail, but being more akin to a coarser overlay that could obscure some of the underlying fine detail.

    Ps, if it matters, the film used was the Kodak professional color neg of the day, either VPSII or III.
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  2. "Unless the dyes react chemically, I'm not sure that blending between layers after processing would necessarily be a problem.."

    - This is getting deep to esoteric now!

    The 'dyes' used in colour film are really dye-couplers - that's half a molecule of dye in simplistic terms. The other half of the (cyan, yellow or magenta) dye is provided by a developer oxidation product, which is common to all 3 dyes. Therefore any mobility of dye-couplers across the 3 colour sensitive layers before development could cause colour pollution.

    To prevent this, the couplers are mixed with an oily substance that reduces their mobility, and also restrains the size of individual dye clouds.

    An homogenous mix of dye-coupler, AgX crystals and gelatine matrix just wouldn't work very well.

    I don't pretend to know the exact details of the chemicals or processes used to anchor the dye-couplers in place. This is just information I've gleaned from various text books and articles over time. AFAIK, it's reasonably accurate.
  3. Interesting, Joe. Okay, thank you. I learn another thing! (Having started with digital, one of these days I'll get all the way back to self-developing film and mastering effective aperture adjustments with focal length on a large format camera. For everyone who finds digital scary, I assure you that going the other way is much more complicated.)
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  4. I agree. Analog refers to electronic technology. Audio tape is analog. The signal recorded on the tape varies as an analog of the pitch and amplitude of the original sound. a CD is digital audio. The original sound is sampled at a very high rate and reduced to a number. That number is etched as a binary number onto the substrate of the blank CD.

    Photographic film is a CHEMICAL process.

    So, the opposite of digital photography is not analog photography, but chemical photgraphy.
  5. Paul: I'm not sure I'd buy that distinction. An analogue computer is still an analogue computer if it works with hydraulics (there are a few examples). Babbage's analytical engine is a digital, mechanical computer. EDSAC and Baby weren't less digital just because they used mercury delay lines and CRT phosphors.

    The opposite of (or at least, alternative to) chemical photography is electronic photography. Older TV cameras (the output of which was recorded on film or tape) were electronic, but definitely analogue. Once everything is quantised to a set of distinct numbers, then it's digital. It's natural numbers vs integers.

    The distinction in this thread was that the activation of silver halide crystals is (as I understand it) digital, specifically binary: they're activated by a photon or they're not. Effectively, the silver halide forms a very fine halftone screen. The complication is that the distribution of silver halide crystals is non-uniform so you don't get a neat grid as with a digital camera. In graphics terms, it's a non-ordered dither. We don't tend to look at the individual crystals, so the resulting image appears to have continuous tone (affected by grain), but at the level of the recording medium, others are right to say it's "digital".

    A photocell, in contrast, actually captures a continuous value (quantised only because of the number of electrons in it); the result is explicitly quantised by an analogue-to-digital converter during sensor read-out, after which the image is "digital" (but not usually bi-level). It then gets processed numerically, of course.

    Of course, it's all quantum if you look closely enough.
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  6. We live in a quantum world, where quantum mechanics applies, not the continuum mechanics that Newton believed.

    Note, though, that the characteristic curves for film curve down, such that the response decreases with increased spatial frequency, not the sharp cutoff that Nyquist indicates for digital.
  7. Nevertheless . . . :rolleyes:
  8. "Note, though, that the characteristic curves for film curve down, such that the response decreases with increased spatial frequency, not the sharp cutoff that Nyquist indicates for digital."

    - By 'characteristic curve' I take it that MTF response is meant, not the H&D curve, obviously.

    Very few digital camera/lens combinations reach the theoretical Nyquist spatial frequency, with the lens being the main limiting factor in the case of sensors with a =< 5 micron photosite spacing. Yet they still convey a far greater impression of sharpness than any film/lens combo.

    Those sensors having a low-pass AA filter are naturally restricted to a spatial frequency below the Nyquist limit.

    The resolution limit for film is set by the average 'grain' size and IME very rarely exceeds 100 lppmm with a very good lens and in the centre of the image circle for slow/medium speed films. Anything with a finer grain structure is almost useless for general pictorial use, and limited to tripod use with static and (usually boring) subject matter and using unreliable processing techniques.

    I still fail to see why the inaccurate use of the word 'analog(ue)' has controversially been introduced, and is being so vehemently defended. It's obviously simply a device to 'hipsterise' the use of film. Such easily swayed individuals rarely have a real commitment to whatever currently 'cool' entertainment catches their interest.

    So what's wrong with the simple, uncontroversial and unambiguous phrase - film photography? Especially when the end output is often scanned, and then definitely enters the digital realm. Thus totally losing any dubious claim to being called analogue.
    Last edited: Mar 15, 2018 at 10:27 AM
  9. Of course, especially in this day and age, and especially on the Internet, a lot of things people claim to be obvious should be taken to be very suspicious. Giving such motives to those who most likely much more innocuously use the term “analog” is probably more projection than obvious.
  10. - Well, someone, or some organisation invented, promoted and propagated the stupid term 'analog(ue) photography'. It's not the sort of phrase that pops into use unbidden and without an agenda.

    I doubt that, at first hearing, the average person-in-the-street even connects the phrase with film photography at all.

    I stand by the hipsterisation theory.
  11. Conspiracy theory much? Pretty natural sounding term to me.
    No doubt.

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