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Author Topic: What is tonality?  (Read 4226 times)

feppe

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What is tonality?
« on: August 02, 2009, 06:56:39 am »

Tonality comes up in discussions quite often, especially when comparing dSLRs to MFDBs, or digital to film. Although it's almost always implied to be a quantitative, objective term, it seems to be used to differentiate between different formats based on qualitative, subjective observations. I'm always suspicious of such hand-waving which reeks of intellectual dishonesty, and am struggling to understand what people really mean when they use that word.

Online searches don't help much: some sources say it is dynamic range, some say it is the contrast curve, or local contrast or microcontrast (which is another vague term), and others say it's the combination of brightness and contrast.

If tonality is DR, then we can easily go to DXOMark site and compare the DR of cameras to determine which one has higher tonality and be done with it (I'll ignore criticisms of their methodology as that's not pertinent to the topic). Comparing film to digital gets a bit more complex due to the linearity of digital, but I'm sure some theorist has done the math already.

If it has something to do with contrast possibly combined with brightness, shouldn't it be a matter of having the right curve, shoulder. If that's the case, it's a highly subjective term and I don't see why a 15 megapixel point&shoot frame couldn't achieve the same curve ("tonality") as a pixel-binned 15 megapixel Phase One 65+ - a rather ludicrous proposition even I admit.

Or is tonality a mainly subjective term which would not withstand a double-blind study of the end results - sadly lacking on photography review sites. That's how I look at it: my 6x6 film photos have much higher "tonality" (as I currently understand it) than my crop sensor dSLR shots, but I'm not at all sure if I could pinpoint the difference in tonality from other people's work.

So, what is tonality?

Jeremy Payne

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What is tonality?
« Reply #1 on: August 02, 2009, 07:58:39 am »

Well ... as I have been taught, tonal range is kinda like bit-depth ... using the ladder analogy ...

If dynamic range is represented by the length of the ladder, the tonal range is represented by the number of rungs.
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Ben Rubinstein

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What is tonality?
« Reply #2 on: August 02, 2009, 08:48:33 am »

I've always understood it as the 'smoothness' of the transition between dark and light.
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ErikKaffehr

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What is tonality?
« Reply #3 on: August 02, 2009, 12:04:48 pm »

Hi,

IMHO tonality is the essentially the gradiation curve. We normally apply an S-curve to our images so we have a steep gradient in the middle tones, making them visually appealing.

Check this article: http://www.normankoren.com/digital_tonality.html

Best regards
Erik


Quote from: feppe
Tonality comes up in discussions quite often, especially when comparing dSLRs to MFDBs, or digital to film. Although it's almost always implied to be a quantitative, objective term, it seems to be used to differentiate between different formats based on qualitative, subjective observations. I'm always suspicious of such hand-waving which reeks of intellectual dishonesty, and am struggling to understand what people really mean when they use that word.

Online searches don't help much: some sources say it is dynamic range, some say it is the contrast curve, or local contrast or microcontrast (which is another vague term), and others say it's the combination of brightness and contrast.

If tonality is DR, then we can easily go to DXOMark site and compare the DR of cameras to determine which one has higher tonality and be done with it (I'll ignore criticisms of their methodology as that's not pertinent to the topic). Comparing film to digital gets a bit more complex due to the linearity of digital, but I'm sure some theorist has done the math already.

If it has something to do with contrast possibly combined with brightness, shouldn't it be a matter of having the right curve, shoulder. If that's the case, it's a highly subjective term and I don't see why a 15 megapixel point&shoot frame couldn't achieve the same curve ("tonality") as a pixel-binned 15 megapixel Phase One 65+ - a rather ludicrous proposition even I admit.

Or is tonality a mainly subjective term which would not withstand a double-blind study of the end results - sadly lacking on photography review sites. That's how I look at it: my 6x6 film photos have much higher "tonality" (as I currently understand it) than my crop sensor dSLR shots, but I'm not at all sure if I could pinpoint the difference in tonality from other people's work.

So, what is tonality?
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Rob C

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What is tonality?
« Reply #4 on: August 02, 2009, 01:23:41 pm »

Perhaps it's simply the effect of the larger negative/source having more room for enlargement before the gaps beween information begin to be manifest.

You can have a beautiful print at, say, 6x9 ins from a 35mm original yet that same original will look different and express a degraded tonality (in my understanding of the word) when it starts to break up slightly as you go to 12x18 ins. Doing the same sizes of print, from 120 originals of the same shape, subject and film-types, you could go larger before feeling that it wasn´t holding its integrity quite as well as it should. To me, this is what we are talking about with tonality. I do, of course, have to assume the same degree of processing expertise being applied in both cases.

An interesting thought, all the same, because one has to wonder if it really is all about continued tonality being expressed in the sense of continuous visual information without the image breakup I refer to above, or whether the same negative, printed through a diffusing filter, would still be able to show the same range of tonality without the sharpness that you have just removed.

I don´t believe it to be a call based on mathematics or a curve which exists within the negative; the negative isn´t changing but the phenomenon we think of as tonality does.

Rob C

feppe

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What is tonality?
« Reply #5 on: August 02, 2009, 02:39:55 pm »

Quote from: Rob C
An interesting thought, all the same, because one has to wonder if it really is all about continued tonality being expressed in the sense of continuous visual information without the image breakup I refer to above, or whether the same negative, printed through a diffusing filter, would still be able to show the same range of tonality without the sharpness that you have just removed.

This is why I'm having such hard time grasping what people mean by tonality - in addition to the vagueness of the term. It makes sense to think about tonality as a separate entity from sharpness as you suggest.

Enlarging an image beyond its original size always results in guessing, through interpolation or more sophisticated methods. Enlarging a 35mm dSLR frame to the same pixel dimensions as MFDB would require quite a bit of guesswork. I know next to nothing about bicubic, fractal or other methods of enlarging an image, but I imagine they all try to guess tones as well as edges.

But if we ignore sharpness in enlarging, interpolating four tones between RGB (255,255,255) and (250,255,255) would be a trivial job for even the most basic algorithm. But going through three pixels with R values of 255, 250 and 200 would be a much tougher challenge due to the way one could interpret the intermediary steps: should the second step be bunched up towards 250, or evenly spaced between 250 and 200? Doing this on a whole 50+ megapixel image in two dimensions and eight to sixteen bits is yet another feat, which might explain the tonality apparent in MFDB files.

ErikKaffehr

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What is tonality?
« Reply #6 on: August 03, 2009, 01:09:55 am »

Hi,

IMHO it's not really possible to increase the amount of information in the picture beyond capture. Interpolation is about smoothing out artifacts. I often ask, myself, what difference there is between MFDBs and DSLRs in different cases. One major issue here is that MFDBs have no optical low pass filter (also known as AA or antialiasing filter). A system without low pass filter will have false resolution when the lens outresolves the sensor, that is has a significant MTF above the Nyquist frequency. False resolution artifacts may give an impression of sharpness unless they show up as visible artifacts. Everyone objects to rainbow colored moiré but not much else.

It may also be the case that MF lenses simply outperform DSLR lenses. MFDBs may put less demand on lens resolution, because of larger pixels, so even if 135 mm lenses normally have higher resolution than MF lenses the MF lens may win when we take pixel size into account. I'd aslo suggest that performance did increase in MF lenses in connection with digitalization. I compared factory MTF curves between the new Hasselblad HC lenses and their Zeiss made predecessors and my impression is that new lenses significantly outperform the old ones. Most of the MTF data I have seen on Mamya lenses was pretty impressive.

The last part of  the equaition is our vision. People have different vision. There is a fundemental limit in the eye, given by distance between the cones that detect light, this is essentially like sensor pitch. It is also my impression that our vision is more sensitive to detail contrast (call it MTF at low frequencies) then resolution (call it MTF at high frequencies).

Best regards
Erik

Quote from: feppe
This is why I'm having such hard time grasping what people mean by tonality - in addition to the vagueness of the term. It makes sense to think about tonality as a separate entity from sharpness as you suggest.

Enlarging an image beyond its original size always results in guessing, through interpolation or more sophisticated methods. Enlarging a 35mm dSLR frame to the same pixel dimensions as MFDB would require quite a bit of guesswork. I know next to nothing about bicubic, fractal or other methods of enlarging an image, but I imagine they all try to guess tones as well as edges.

But if we ignore sharpness in enlarging, interpolating four tones between RGB (255,255,255) and (250,255,255) would be a trivial job for even the most basic algorithm. But going through three pixels with R values of 255, 250 and 200 would be a much tougher challenge due to the way one could interpret the intermediary steps: should the second step be bunched up towards 250, or evenly spaced between 250 and 200? Doing this on a whole 50+ megapixel image in two dimensions and eight to sixteen bits is yet another feat, which might explain the tonality apparent in MFDB files.
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