photoshop brush woes

[arch-fiend]

hello, i'm not the most experienced user of photoshop but i think of myself as someone who has been around with several image tools in my time. anyway my problem with photoshop is probably a strange one and somewhat complicated one but ill try my best to explain it as well as i can starting with a preface.

from what i can tell about the way photoshop "does" brushes is by taking a picture, convert it to greyscale, then set an opacity with light values being more transparent than dark values. then to make this image a brush it stamps it onto your canvas every time you move your mouse over a number of pixels.

now knowing this my real issue really is about how photoshop hands opacity on a single layer, when values with opacity are added to each other on the same layer it adds them together and it mixes the colors together if they are different but also causes that area to be less transparent as well. what i want to know, is there a way to paint a line then paint another line without where they cross being added together?

[Diamond]

I think I understand what you mean. And as far as I know, the answer is no, if you're doing all this on a single layer. The only way I know to do it is use two (or more) layers, choose one layer as a selection and use it to erase the part of another layer that's on top of that selection.

[arch-fiend]

alright, i will give that a try