Processing the Swoosh

Next, as we remain on the layer with the gradient, we go to [ Filter -> Pixellate -> Color Halftone ]. This filter allows us to creat that halftone effect you see in comics, or color newspapers. If you look close enough at a colour print in a newspaper, you will see that the colors are composed of only 4 color (Cyan, Magenta, Yellow and Black) dots that are offset in relation to each other.

For the pixel radius (radius of our dots) we select something that makes sense in relation to the size of our canvas. The Screen Angles should all be set to the same value, however, you can play with the actual values and see how close you'd like to get the dots together. We make the angles the same so that all the "colors in our print" overlay each other and result in black dots. (Credit goes to this Graphics.com comic art tutorial).

The goal for the next step is to get rid of all the white areas in our swoosh and leave just the dots. To start, we need to make the smaller gray dots at the right end of the swoosh much darker than they are now. To do that, go to [ Image->Adjust->Levels ]. Adjusting levels is another one of those things that are difficult to master but very useful - it allows you to regulate just how dark or light the highlights, midtones and shadows are in a picture. Play with this tool until the gray dots become black, but the black dots are still crisp. The picture below shows the darkness and contrast we're aiming for: Note that all this while we are working on just the swoosh layer. Make the background layer invisible.
Next, we want to create a selection based on a certain color. For that we go to [ Select -> Color Range ], we use the pipette tool to click on the white area, and we adjust our selection with the Fuzziness factor. We want to select around all of those small circles, instead of losing them. After you are done creating the selection (having selected the white areas), press DELETE. Then go to [ Select -> Inverse ] to select all those black circles that are left. This is what it looks like: Hang on! We're almost there!
After you have the black areas selected, fill them with a colorful gradient. Notice, towards the top middle of the swoosh, that we have a line going along the outline of the swoosh - we just want the dots, so lets get rid of that line. Go back to the Paths Window, select the swish path and click on the rightmost option at the bottom - make a selection out of our path again. Now, we want to select a band that runs along the path, not just an area inside or outside. For that we can go to [ Select -> Modify -> Border ], this lets us create a border selection. Enter the pixel width of the border you want and make sure that it encompasses that line we want to get rid of. Take a look at the resultant selection below. Delete that region. Ok, at this point our swoosh is done. Play around with the blending mode to see what works nicely with your background (I have the mode set to Screen below). Select the swoosh layer, go to [ Layer -> Add Layer Mask -> Reveal All ]. This will create a special Mask Layer where any dark areas in the mask will cause the underlying layer's areas to be invisible. We want the swoosh to look like its behind the woman's head, so for that create a path like the one below where her head would overshadow the swoosh. Go to the Paths Window, select it, create a selection from it and fill it with black. Look at what happens below. To quickly fill an area with black, go to [ Edit -> Fill ] and select Black. At this point we are done. Play with the blending options, or use the Eraser tool to soften the sharp outer edges of the swoosh. You can also make the inner transition from larger dots to smaller dots smoother if you use the Eraser tool on it.