histogram of a region

[bwana]

is there any software that will generate a histogram of a region i select? yes i know i could copy a region, paste it into a new ps doc and look at that histogram, but that really is a bit of a pain when i  want to look at multiple parts of my image.

also, is there an application that will highlight the pixels of my image based on my selection in a histogram? I might want to see more precisely where a particular band of brightness lies in an image. then I want to see how that pixel collection changes as i move the brightness level gradually up or down. 

[Schewe]

Part 1-Photoshop...do a selection and update the histogram and it will display the histogram of the selected areas...

Part 2-none that I know of...

[milt]

For Photoshop CS4 and up, the "finger" tool of the curves adjustment layer shows a mark on the histogram for the area under the mouse pointer.  This is kind of the reverse of what you want, but it would allow you, by searching around with the mouse, to find the various parts of the image that contribute to some particular part of the histogram.

--Milt--

[RFPhotography]

also, is there an application that will highlight the pixels of my image based on my selection in a histogram? I might want to see more precisely where a particular band of brightness lies in an image. then I want to see how that pixel collection changes as i move the brightness level gradually up or down. 

I might be wrong but it sounds like you're looking for something like a luminance mask.