1. Take an image (like the coaltongue)
2. Image->Adjustments->Desaturate
3. Duplicate the layer (Ctrl+J)
4. Select the new layer
5. Set this new layer to 'color dodge' (top of the layer panel, just under the layer tab)
6. Invert the new layer (Ctrl+I)
7. Apply a gausian blur filter to the new layer (Filter->blur->gausian blur)
7b. Set the radius for 10 pixels or so (in the gaussian blur window that pops up)
8. Click on 'create new fill or adjustment layer' (center bottom of the layer panel)
8b. Choose 'levels'
8c. Slide the darkest marker under the graph up to sharpen/darken the image (in the adjustments panel)
9. Select all the layers
10. Flatten the image (Ctrl+E)
11. Copy the entire image (Ctrl+A then Ctrl+C)
11B. Seriously, copy the entire image, and don't put anything else in your clipboard, or go paste the image somewhere convenient so you can get it later
12. Set the image to grayscale (Image->Mode->Grayscale)
13. Change the image to a halftone bitmap (Image->Mode->Bitmap->Yes, flatten layers)
Don't mess with the resolution if that window pops up, just hit 'OK"
13b. Halftone Screen:
-Frequency: 16 lines/inch
-Angle: 45
-Shape: Line
14. Either:
A) you're done and like the lined halftone
OR
B) Paste that old image for a grainy, woodcut look