From black point to white point

[Abitconfused]

A Curves Adjustment Layer may be divided into Black Point, Three-quartertones, Midtones, One-quartertones and White Point. Are shadows and three-quarter tones the same thing? And are one-quartertones highlights?

[pnodrog]

Even if the exposure was correct it will depend on the definition you are working with regarding shadows and highlights....

If you use the definition of shadow and highlights as the regions where detail can still be detected they will probably fall a bit closer to black or white points than the 1/4 or 3/4 tones. In general discussion I find that when using the terms shadow and highlights photographers are referring to area's that have a little more detail than the more formal definition refers to.

I will watch this thread with academic interest as in practice I just adjust the curves so the image is as I require it when viewed on my monitor. In the good old days some photographers would refer to "zones" which was/is a bit better defined.

[IzzieK]

Me too...+1 to Paul's comments...

[James G]

Ed, shadow and highlight are subjective terms which are not particularly susceptible to measurement using absolute luminance/brightness scales.

They are comparative terms and as such cannot be 'confined' to limited areas of an absolute scale.

The shadow of a tree is simply the area behind the tree where occlusion results in less/no direct light illuminating that area. Highlight could be seen as similar but a way of describing relative brightness. The problem is that the shadow could be the result of strong or weak illumination, which in turn introduces more comparative terms.

So, for me , no, shadow and highlight cannot be defined completely the way you seem to be suggesting since, as Paul has already indicated you would have to find some 'absolute' way of defining shadow and highlight which then effectively removes any comparative function...... I think that makes sense.....

Paul also mentioned the zone system, which I still use occasionally as a way of assessing 'difficult' lighting scenes. In that context the terms highlight and shadow are used for zones that are otherwise simply tagged numerically. But, the zone system itself is comparative rather than an absolute system

[Mike Buckley]

The Google/Nik Silver Efex Pro, which is free, includes a tool that displays where each of the 11 zones are located within the image.

[chauncey]

Doing all of my work in PS, I tend to use "color pickers"...setting my whites about 247 and blacks at 6.

[Manfred M]

Ed - there can be shadow detail even in the lighter end of the scale. If I recall correctly, Zone VIII (from the Adams & Archer Zone System), which would be in the highlight tones area of your histogram, is where we see texture in snow. Snow is white, so the texture has to come from shadows; so there is shadow detail even in the highlights. Zone 0 would be anything to the left of the black point and Zone X would be anything to the right of the white point on the histogram.

[Mike Buckley]

Snow is white, so the texture has to come from shadows; so there is shadow detail even in the highlights.

Manfred makes an excellent point. To take it one step farther, consider the luminosity value of shadow tones of snow on a barren, flat field lit only by the bright sun from the right. Now consider the exact same situation except that the white wall of a barn is reflecting light into those shadows from the left. In the first case, the shadow tones will be relatively bright because snow is relatively bright. In the second case, the shadow tones will be even brighter thanks to the white wall acting as a reflector.