I’m going to show you a quick way to turn a photo into a facsimile of one of those posters. Here we go!
To start, I’m using a cool skull photo from the folks at Photos.com.
Go to Select>Color Range. In the dialog box, change the Selection Preview to Black Matte and set the Fuzziness to 30-35. With the Eyedropper, make a selection on the image so that you get a nice but subtle outline of the skull; enough so that skull-like features appear, but not so that the entire skull is selected. Clicking on some of the bone around the eye is a good place to start: to add more, simply hold down the shift
key and click again. This will add more to the selection. If you feel you get too much, release the shift key and try again.
When you are happy with the selection (it should resemble the image above) click OK. The matte will disappear, leaving a selection on the image corresponding to the color range you choose.
Go to Layer>New> Layer via Copy.
We want to regain the black matte effect, so create a layer beneath the one you made in the previous step, and fill it with 100% black.
The image will now appear something like this:
Duplicate the skull pixels layer twice, and then select the one just above the black layer.
Turn off the top two layers so that you can see the one selected clearly. As I recall, black lights only appeared black when they were shut off: the bulb when turned on was actually a shade of purple. Using the Hue>Saturation adjustment to turn the selected layer purple.
Now apply an outer glow to the layer with the Layer Styles dialog box. Use the settings seen below. I’m using a fairly hi res image, so the size of the glow needs to be large: if you are using a copy of the image capture here, then you will need to use a lower setting.
Once the glow is in place, I’m simply going to duplicate the glowing layer a couple times to enhance the effect, and then duplicate the top layer a few times to brighten the yellowish pixels comprising the skull.
My resulting Black Light poster is seen in the following image.
Try experimenting on photographs other than skulls; you will get some rather interesting effects. The following image uses the same technique, but without the glow.