Help understanding terms - Tonality vs Contrast.

BradS · Jun 16, 2021

Please help me understand the difference between tonality and contrast. It will may be clearest if it con be explained in terms of the H-D curve.

slope of the curve is related to...
range of values spanned on the vertical axis is related to...

or something else?

Thanks in Advance.

distributed · Jun 16, 2021

... and let the discussions begin!

Looking at a HD curve I say that the slope corresponds to contrast. A steep slope means high contrast, a flat slope means low contrast. In this definition, contrast is a measure of how much density change is produced in the output medium when the process is presented with a given exposure change.

The range of values spanned on the vertical axis is the density range. For instance a reflection density range of 2.0, typical for B/W papers, gives you a factor 102 = 100 in reflected light intensity between the lightest and the darkest parts. Confusingly this brightness factor is what is called "contrast" in LCD monitors.

I would describe tonality as how the tones of an image look like. It's a highly subjective term.

BradS · Jun 16, 2021

ah, yes....but we get immediately to heart of the matter...(Thanks!)

if the slope of the line is smaller, then for a fixed range of exposure (horizontal axis), the range of densities (vertical axis) is smaller - right?
so is contrast defined in terms of slope or range of densities?

Bill Burk · Jun 16, 2021

In terms of contrast, the measure is from one end to another, it’s a single number, the measure of dark to light. It gives you a good idea whether you picked the right development time. There are different measures but those are concrete.

Tonality is the subjective one worth hearing opinions of people who know what they like.

There are different places where people like the curve flatter (shadow) and steeper (faces). So a nice curve has a long toe and slight upward bow near the high gray tones returning to a normal straight line into the highlights without shouldering too soon. Then to use this nice curve properly for portraiture, you would expose to put shadows on the toe and faces in the upward bow.

It’s all very slight in the curves but the curves are logarithmic so a little goes a long way.

There is the paper curve to consider. Here you have a shoulder (in the shadows) and a toe (in the highlights) to contend with.

Sirius Glass · Jun 16, 2021

While tonality can be subjective, I take it to describe how smoothly gradual transitions between light are portrayed on film. The worst case can be described as a smooth transition is rendered as bands instead of how it really appears.

wiltw · Jun 16, 2021

Think of contrast as the ratio between the extremes, black vs. white. Poor contrast could have no black and no white, only greys. A foggy scene inherently has low contrast, no fault of exposure or development.

Max contrast with poor tonality in between is conceptually tone 0 (black)vs. tone 1 vs. tone 2 vs. tone 3 (white)
Max contrast with good tonality in between is conceptually tone 0 (black) vs. tone 1 vs. tone 2...vs tone 126, vs tone 127 (white)
Max contrast with super tonality in between is conceptually tone 0 (black) vs. tone 1 vs. tone 2...vs tone 12766, vs tone 12767 (white)
Poor contrast with good tonality in between is conceptually tone 20 (grayish black) vs. tone 21 vs. tone 22...vs tone 101 vs tone 102 (grayish white)

distributed · Jun 16, 2021

BradS said:
if the slope of the line is smaller, then for a fixed range of exposure (horizontal axis), the range of densities (vertical axis) is smaller - right?
so is contrast defined in terms of slope or range of densities?

I say it is defined in terms of slope. As michael_r said, "contrast is the slope of the H-D curve of between any two points".

You will encounter the word used differently. For instance when wiltw refers to a "foggy scene ... [that] has low contrast" he is not speaking about a slope, but about the subject brightness range (SBR) of the scene being small.

Whenever I read "contrast" I pause momentarily to be sure that I understand which definition of contrast is at play.

distributed · Jun 16, 2021

Maybe that was too quick of me. If speaking about HD curves, grades, adjusting negative development etc. I would assume that contrast refers to the slope. In many other areas of life contrast refers to the a difference in brightness or otherwise measured quantity. Compare the definition of contrast given by Wikipedia: "Contrast is the difference in luminance or colour that makes an object (or its representation in an image or display) distinguishable."

ic-racer · Jun 16, 2021

Contrast is a measure of light and dark areas. Toning affects a prints color.

BradS · Jun 16, 2021

distributed said:
... and let the discussions begin!

Looking at a HD curve I say that the slope corresponds to contrast. A steep slope means high contrast, a flat slope means low contrast. In this definition, contrast is a measure of how much density change is produced in the output medium when the process is presented with a given exposure change.

michael_r said:
Contrast is the slope of the H-D curve of between any two points.

Tonality is a wishy washy term that can mean different things depending on who you are talking to. It can be an broad descriptor of a print (for example if someone says rich tonality, harsh tonality, muddy, high key, soft etc. whatever word). It is also sometimes used as basically a synonym for the H-D curve itself (since that is what the curve describes), or a portion of the curve (highlight tonality etc.). Concerning prints, it is also often used in reference to the colour (cold, warm etc.).

There is a more rigorous thing called tone reproduction, which maps how the luminance values in the original scene are ultimately rendered in the final presentation medium (print etc.). In the case of B&W negatives for example, basically a series of H-D and other curves showing the transitions from scene->imaging system->negative->print.

This makes sense and defining contrast in terms of the slope is simpler and perhaps, generally, more useful.

The surprise for me is that tonality is subjective. I've never given it much thought. I could never figure out quite what it meant, I guess because people use the term to mean so many different things.Knowing that it is a subjective thing makes it much less confusing (although, it also makes the term kinda meaningless).

Thanks.

warden · Jun 16, 2021

BradS said:
This makes sense and defining contrast in terms of the slope is simpler and perhaps, generally, more useful.

The surprise for me is that tonality is subjective. I've never given it much thought. I could never figure out quite what it meant, I guess because people use the term to mean so many different things.Knowing that it is a subjective thing makes it much less confusing (although, it also makes the term kinda meaningless).

Thanks.

The subjective part is where it gets interesting I think. I like the description @Bill Burk made above, where the intent is to capture a particular contrast (tonality) in a portrait, especially getting the steep part of the curve on the face skin tones and letting the shadows flatten out. If he were to get it wrong and the face ended up on a less desirable (flatter, lifeless) part of the curve he would probably describe that as "bad tonality" for his portrait, even though he got full contrast from white to black on the negative, and then try to fix it in the darkroom somehow.

When I look at a negative that's how I think of tonality: did I get the right part of the image on the steeper part of the contrast curve? Or did the part of the image that I thought was important get washed out and de-emphasized by ending up on a flat-ish part of the curve?

cliveh · Jun 16, 2021

Contrast is a measure between black and white. An elephant is low contrast and a Zebra is high contrast. In terms of characteristic curves, the steeper the curve (on a negative) the higher the contrast. A shallow curve will give low contrast.

Tonality may be expressed as the number of grey variations between black and white, The greater the variations shows greater tonality. Less variations shows less tonality.

That is my take on it.

takilmaboxer · Jun 16, 2021

I've always understood tonality to refer to how film renders colors as shades of gray. Film is not color blind; it is more responsive to blue light than other colors; it usually has a dip in the green; and films vary in their sensitivity to red light. If you shoot the same landscape with orthochromatic film, old school panchromatic film, and Tmax 100, the resulting prints will have noticeably different tonalities, and different ways of relating the various shades of gray. Tonality is subjective and therefore subject to often dramatic differences of opinion. As you may discover as this thread develops.

MattKing · Jun 16, 2021

I am going to differ from Bill Burk - something I almost never do.
"Contrast" probably needs a modifier.
If you are talking about the entire print, it probably should be qualified as "total contrast", although I prefer to talk about the range of d-max to d-min.
That is the objective measure. Subjectively, people tend to describe prints with large areas of deep black shadows and just a few small highlights as being "contrasty". A print like that can actually have the same total contrast as a snowman in a snowy field with a nose of just one piece of coal.
If you are talking about how well details in the shadows are delineated, "shadow contrast" is a more useful description.
The same applies for mid-tones and highlights.
Tonality - that is an imprecise something that refers to how the different contrasts in a print get along together. A print with good transitions between the contrast in the shadows, to the contrast in the mid-tones, and then the contrast in the highlights.
In all cases though, contrast itself is a reference to slope.

runswithsizzers · Jun 16, 2021

cliveh said:
Contrast is a measure between black and white. An elephant is low contrast and a Zebra is high contrast. In terms of characteristic curves, the steeper the curve (on a negative) the higher the contrast. A shallow curve will give low contrast.

Tonality may be expressed as the number of grey variations between black and white, The greater the variations shows greater tonality. Less variations shows less tonality.

That is my take on it.

Something like this has been my assumption, as well.

If we limit the discussion to black and white prints, then each paper is going to have a maximum black and a paper white, right? And if a tone is defined as a shade of gray - that is, a step part-way between black and white - then, practically speaking, there are a finite number of tones between max black and paper white. I expect the exact number of tones probably varies somewhat depending on the perception of the viewer, but as the difference between each step gets smaller and smaller, at some point most people are going to see adjacent steps as the same shade of gray. Once a print includes every discernible shade of gray between black and white, it has the greatist possible tonality. Because different papers have slightly different maximum black and paper white, each paper has a somewhat different potential for tonality.

But I think there is probably more to it than that because human perception is tricky. A given shade of gray will appear darker or lighter depending on what shades surround it. Some subjects, under certain lighting may appear to present more shades of gray than they really do. Because of the satisfying way various shades of gray may appear when adjacent to each other, the right subject under the right lighting may appear to be very rich in tones - and we might subjectively say a print has good tonality - even if not every shade is actually represented. I think this definition goes along with what MattKing said in post #16 - "...an imprecise something that refers to how the different contrasts in a print get along together."

Bill Burk · Jun 16, 2021

MattKing said:
I am going to differ from Bill Burk - something I almost never do.
"Contrast" probably needs a modifier.

No worries- I should limit my comments to the part I know and leave the rest to you.

I meant to add modifiers to clarify I was talking only of “Contrast” as it relates to a measure of the amount of developing a film received, and there we have concrete definitions of “Contrast Index” and the “ASA parameters” (and other measures like gamma).

Sure a scene can be contrasty, and a lioness can hide from a Zebra because she has low contrast fur that blends well with the grasses. And a paper and a print can be contrasty. I meant to leave those meanings out.

When it comes to tonality I am not the expert. I use the straight line as much as possible.

distributed · Jun 17, 2021

I can recommend the book "Post Exposure" by Ctein as it touches on a number of interesting subjects. For instance about tonality, see Chapter 1, subchapter "Our Vision of Tonality".

The book can be downloaded for free on the author's homepage: https://ctein.com/booksmpl.htm

alanrockwood · Jun 17, 2021

I'm glad to see this discussion because I too did not know what people were talking about when they use the term "tonality."

It looks to me like it means different things to different people. However, I thought the comment by Bill Burk was insightful. What if we were to extend this idea to something like this. "Nice tonality is when the steepest part of the contrast curve is more or less centered on the subject of interest." The subject of interest could be the face when dealing with portraiture. If it's a face, "nice tonality" might mean something different for a Caucasian face than it would for an East Asian face, and something still different for a South Asian face or African face. Speaking as a non-expert here, you might want to increase development to get better contrast in the toe if you are photographing and African American, and you might want to pick a film/developer combination with more shoulder to avoid blowing out the highlights. Obviously, you wouldn't want to take this to extremes because you don't want to make an African American look white, but you probably don't want to have the African American face to lose so much contrast that it just looks like a dark shadow, so you probably don't want it deep down in the toe.

There is probably something you would want to do with adjusting exposure as well.

Are there any books on optimizing portraiture technique for different skin tones? I might be particularly interested in this because I have some African American nephews and nieces, and it could be good to take some nice portraits of them. On the other hand, most of the family is pretty much lily white, though I do have a Mexican American cousin-in-law who's complexion is quite dark, and a niece-in-law who is East Asian. Then there is one daughter and one grand daughter who's skin tones are fairly light olive, just like my grandmother's skin was when she was alive. (I guess that pretty much covers the gamut of skin tone doesn't it? And in just one family at that!)

Does that sound reasonable?

cliveh · Jun 17, 2021

I would also suggest that when using the word tonality, it is a more meaningful word when discussing it in terms of the context of the subject within a print. A scene from Macbeth requires different tonality than say a picture of a baby. So, appreciation of tonality is largely married to the subject matter of the photograph.

RalphLambrecht · Jun 17, 2021

Sirius Glass said:
While tonality can be subjective, I take it to describe how smoothly gradual transitions between light are portrayed on film. The worst case can be described as a smooth transition is rendered as bands instead of how it really appears.

this hits thenail right on the head fo me!

warden · Jun 17, 2021

distributed said:
I can recommend the book "Post Exposure" by Ctein as it touches on a number of interesting subjects. For instance about tonality, see Chapter 1, subchapter "Our Vision of Tonality".

The book can be downloaded for free on the author's homepage: https://ctein.com/booksmpl.htm

That was an interesting essay, thanks!

ic-racer · Jun 17, 2021

Tonality is the color due to toning. Other uses of the word in B&W print making are made-up, have no definition. This is 100% an "IGNORE" thread.

BradS · Jun 18, 2021

ic-racer said:
Tonality is the color due to toning...

What is the source of this definition?
Can you please provide us with a reference?

BradS · Jun 18, 2021

distributed said:
I can recommend the book "Post Exposure" by Ctein as it touches on a number of interesting subjects. For instance about tonality, see Chapter 1, subchapter "Our Vision of Tonality".

The book can be downloaded for free on the author's homepage: https://ctein.com/booksmpl.htm

Thanks!

wiltw · Jun 18, 2021

RalphLambrecht said:
this hits thenail right on the head fo me!

Indeed. Back in the 'old days' when we spoke of using the same emulsion in both 135 and in Medium Format, 'tonality' was said to be better on the medium format shot, simply because (linearly) there were twice as many film grains across the (about) 2x longer film capture area which captured the same scene. So in the negative the transitions of tonality were spread out across more film grains, with better spatial spreading of the transitions in tone which occurred across the subject, so medium format allowed better capture of those transitions. That is, "how smoothly gradual transitions between light are portrayed on film."

Help understanding terms - Tonality vs Contrast.

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