What exactly is tonal contrast?

[Lesley Jones]

While I'm in the mood for silly questions, can anyone define tonal contrast please? A professional photographer from another forum used it for increasing texture, but he was adamant it wasn't the same as sharpening. I don't get it though because isn't sharpening just increasing the contrast between edges? I like using a bit of selective tonal contrast - to my mind it does add texture and detail too, which can be further enhanced by careful sharpening later. If I've already boosted the local contrast though, should I beware of any horrors when doing a final sharpen for using in here? I'm not very good with sharpening at all, having very bad eyesight. I can't be doing with all those sliders so I use Photokit for capture sharpening and Topaz Infocus for the finished article. I don't think I've ever noticed halos, but could they be lurking in the shadows?

 

[Hamish Gill]

As I understand it ...

Tone is intensity of light and dark, so tonal contrast is the difference between light and dark ...
Tonal contrast is just surely just contrast?

What your mate is talking about is edge contrast ... Like "clarity" in LR ... Which is I suppose a little like sharpness ...

Dunno, that's how I understand it

 

[Lesley Jones]

Hmm... I'm getting really confused now. I use a bit of the clarity slider in RAW and thought that was the mid tone contrast. I actually never use the contrast adjustment layer on my images - I hate it because to me it seems to pull the image apart. I will amplify whites and blacks in Silver Efex, but only on small areas. Ditto a bit of local contrast, but again... in a small and selective way. The tonal contrast filter in Nik Color has sliders for highlights, midtones and shadows, so perhaps it's local contrast in certain tones only. I hadn't realised, but if you pull all three sliders over to 100% you end up with an OTT HDR effect. I found that by Googling tonal contrast earlier

 

[Dan Cattermole]

I wish I was sober to reply! lol
I have an idea in my head but really struggling to evplain what it is I;d like to say.

 

[Kev Pugh]

I wish I was sober to reply! lol
I have an idea in my head but really struggling to evplain what it is I;d like to say.

Muppet....

 

[Dan Cattermole]

I love it!!!

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[Chris Dodkin]

Good write up here Lesley: How to Enhance Texture with the Tonal Contrast Filter in Nik Color Efex Pro

And also a note at the end on using the effect in reverse to smooth skin on portraits.

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And a great one here on using the effect on a B&W image, still in Color FX though!

http://blog.bretedge.com/2011/08/25/make-skies-pop-with-nik-color-efex-pros-tonal-contrast-filter/

 

[Lesley Jones]

Thanks for that Chris. As soon as I saw the door I remembered that I read the article some time ago. I'm not even sure if I was using Color Efex back then. I have actually used negative tonal contrast with some of the babies I edited and it worked to some extent when I had sky banding problems before I got CS5 and was still working in 8 bit. I still don't understand why using tonal contrast with all three sliders makes the image look different to an overall contrast adjustment though...

 

[Lesley Jones]

OK - time for a little experiment. I've taken a bog standard photograph that's had virtually no processing. I didn't know how back then. I'll try to put them side by side. The one on the left is with 20% contrast. The one on the right is 20% tonal contrast (all three sliders). Both images sharpened the same...

 

[Hamish Gill]

So is clarity in lightroom tonal contrast then?

 

[Pete Askew]

I think of it as being another way of doing a curves adjustment. In both you are affecting the contrast more with some tones than others. The sliders under the curve in LR do a similar job but with the Nik tool you can be very selective with control points; rather like using different grades when burning multi-contrast B&W paper.

 

[Pete Askew]

Sorry, I was answering Lesley and not referring to Clarity which used to affect edge contrast and general contrast in the mid-tones. It seems it now extends beyond that in LR4 and affects exposure also. It's seems to be a bit like structure in Nik SilverFX. So they all do similar things but in slightly different ways it seems.

 

[adrian jordin]

Tonal Contrast filters work on the small detail within an image rather than on larger areas of a picture as a whole.
A special algorithm will identify areas of small detail and allow the contrast between the tones just in those areas to be increased.

So, pebbles on a distant beach each with their own small shadow may not stand out till you increase the contrast between the tones in each pebble and shadow. This gives the effect of enhancing the detail and making things look sharper.

You can see this in Lesley's examples.

 

[Lesley Jones]

It's getting too complicated for me, but Adrian's explantion makes sense. I've used tonal contrast very successfully in images with tiny details - like bird feathers or ferret hair. I'm not even sure I should be asking this, but is this similar to the micro contrast sharpening I have in Topaz Infocus? It seems to enhance very small details, like grass for instance.

 

[Hamish Gill]

I get confused with all these different terms ...
I have this conflict in my head between the idea that I should be learning more so get better and the idea that I don't need to know the technical details of what I'm doing to hone my pp skills - as really, I get better through just playing with it all anyway...
i think the first is probably the better option long term, but sometimes it seems to detract from the "arty" "creative" enjoyment of things when you try and apply technical knowledge

Still, one way or another your (obviously not) "silly" question has taught a few of us something

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Just to add, this tonal contrast ...
Somthing I couldn't get my head round for ages was lens contrast
i always assumed lens contrast was a images wide thing to do with differences between lights and darks (why is it so hard to define contrast anyway??)
its not to do with that at all, it's actually microcontrast, ie how a good a lens is at differentiating between smaller and smaller difference in tone ... Something like that ...
Sound similar to what we are talking about adjusting in this thread somehow??

 

[Hamish Gill]

Sorry ... Smaller and smaller differences in smaller and smaller areas of tone .. Is that right? It makes sense in my head

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Another question then ...
Is this abilty to adjust tonal contrast something born ou of digital process?

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Sorry, I was answering Lesley and not referring to Clarity which used to affect edge contrast and general contrast in the mid-tones. It seems it now extends beyond that in LR4 and affects exposure also. It's seems to be a bit like structure in Nik SilverFX. So they all do similar things but in slightly different ways it seems.

Yeah ... It's much stronger, but you don't get so much of the haloing ... It seems to me that the effect on exposure has come from the need to remove that halo effect.
So where it would before make halo light or dark edges those edges now spread to effect greater areas ... Dow arhat make sense?

 

[Pete Askew]

Good description Adrian. I'm not sure that the algorithms work on size of areas more than areas where change is at a higher frequency. The effect is the same though. I guess the result is the same for all contrast calculations whether they be related to a lens or the image; it is about the ability to differentiate small differences in contrast at adjacent points (or in global contrast - the overall scene). The optics of a system play a role in this as does the resolving power of the sensor / film. In analogue photography the rest of the process is controlled by the sensitivity characteristics of the film, how it is developed and on the grade of paper it is printed on and the development of that (and, in the case of B&W, any toning etc). In the digital domain there are lots of ways to process the information to either increase the overall contrast or those at finer levels of change or in areas where there are many areas of change. The trouble is, the names they give these processes is not very clear (much as with the splitting of contrast into 'global' and micro-contrast). There are some good books on this subject for analogue photography and for lenses but I have yet to find something that I understand clearly for the various digital processes. I guess the mathematics is complex and that several things are combined in proprietary ways to get the effects that we see. That's why I like to think of these things in terms of sensitivity curves although there is clearly more going. There must be something out there.