I am thinking belatedly that there might be some confusion after my last webinar about what exactly I was referring to as 1/4 tones, midtones, 3/4 tones etc. Coming from the background I have in pre-press and actually having to run a small press oh so long ago, I take it for granted that the meanings of those terms are common knowledge.

Here is a breakdown for you to follow:

RGB world:

0-32 would encompass your shadow area's
32-96 would encompass your 3/4 tones with 64 being your center point
96-160 would encompass your midtones with 128 being your center point
160-223 would encompass your 1/4 tones with 191 being your center point
223-255 would encompass your Highlights

CMYK World:

0-12.5 encompass your highlight
12.5-37.5 encompasses your 1/4 tones with 25 as the center point
37.5-62.5 encompasses your midtones with 50 as the center point
62.5-87.5 encompasses your 3/4 tones with 75 as the center point
87.5 to 100 encompasses your shadow area's

Please keep in mind that when deciding what is what with the image you are working that THAT image decides what is what. It could be that the heaviest portion of the image is 85%. Therefore that is the shadow of the image.

Some old timers out there might object strenuously for the above comment about judging each image in its own right. All I can say is it works for me and always has. When you are looking for a dot/pixel at 85% and one does not exist whats the sense in moving a curve at that point? Or if it is indeed the heaviest pixel reading in the image why make the mistake of opening the image from that point and flattening it out?