The Extreme Contrast Effect:
I'm still not very sure when this effect works the best. I guess the more the photo has bright colors, the more it looks great with it.
Anyway, I'll use this photo of Pooh reading a book about PHP. I took it using my Nokia cell phone's camera. Not a high resolution photo at all.
Step 1: Duplicate the background layer by clicking the keyboard shortcut Ctrl+J. This will add a new layer called "Layer 1".
Step 2: Desaturate the new layer by hitting the keyboard shortcut Shift+Ctrl+U to make the image appears in black and white.
Step 3: With "Layer 1" selected in the Layers palette, press Ctrl+J to duplicate it, so we'll now have two black and white layers in the Layers palette.
Step 4: With "Layer 1 copy" selected, change the blend mode of it to 'Screen' and lower the opacity to 50%.
Step 5: Click back on the original Background layer. Then press Ctrl+J to create another copy of it, named "Background copy". Then drag & drop it to the top of the layer stack.
Step 6: Change the layer's blend mode to "Overlay", and the opacity to 75%.
Step 7: With the "Background copy" layer still selected, press Shift+Ctrl+Alt+E to merge all layers onto a new layer at the top of the layers palette.
Step 8: Add noise to the merged layer [Filters > Noise > Add Noise]. And use the values of the following screen.
Aside: Well, feel free to set the "Amount" of noise you'd like & that suits your photo.
Step 9: Sharpen the image to enhance the noise [Filter > Sharpen > Smart Sharpen]. Use the following settings.
Step 10: Add a "Curves" adjustment layer [Layer > New Adjustment Layer > Curves], and set its blend mode to "Multiply".
Step 11: Grab the Elliptical Marquee tool from the Tools palette, and drag out a large oval selection inside the document, making it so large that the edges extend out past the left and right of the image.
Step 12: With Black color as your Background color and the Curves adjustment layer selected in the Layers palette, use the keyboard shortcut Ctrl+Backspace to fill the selection with black. You're not covering the image itself with black. Instead, you're filling the area on the Curve adjustment's layer mask with black, which will cause the Curves adjustment to be hidden inside the area you selected, allowing the original lighter version of the image below it to show through. Only the corners of the image remain darker.
Step 13: Soften the edges with the "Gaussian Blur" filter [Filter > Blur > Gaussian Blur]. Use the following settings.
Aside: Again, this depends on the resolution of the photo. So, change the value till you get a smooth enough edges.
This is the last step to have an Extreme Contrast effect on your photo. For this particular one, I'll add some blur effect to the background, to make Mr Pooh stand out of it.
So here's the final result. Click to enlarge.