In order to make the image "pop" I usually add a sharpening effect in order to bring out the details and make the image easier to read. I usually use an unsharp mask, but it is possible that other sharpening filters are better. It's all up to you.
Combine: Create a new layer on top of the entire stack and press Ctrl + Shift + Alt + E to merge all visible layers into the active layer.
Apply an unsharp mask: Choose Filter > Sharpen > Unsharp Mask. I usually set amount quite high and later control the amount with the layer opacity. Radius should be below one pixel in my opinion (Fig.42 - 43).
Fig.44 - 45 show the before and after shots.
Grading and Noise
After applying all the light passes it is always good to do a final grading. It's like the last tuning of the colors and intensity of the image. Adding noise to the image adds to the realism as well.
Add noise: Create a new layer and fill it with 50% gray. Then go to Filter > Noise > Add Noise. Set that layer's blending mode to Overlay. Play with opacity and make it subtle (Fig.46).
Add grading/adjustment layers: Add a Curves adjustment layer (Fig.47) and then edit the curves as follows:
? Curve 1: Blending mode = Normal. This curve generally brightens the image.
? Curve 2: Blending mode = Normal. Here I decided I wanted more brightness. It could have been done in Curve 1, but I thought I would have more control with a second curve.
? Curve 3: Blending mode = Color. This curve is where a lot of magic happens, in my opinion. I adjusted it so blue and green is added to the darker parts of the image, and blue and green is removed from the brighter parts. The effect is that you get a really dynamic color spectrum to the image and somehow it does not look so "flat" anymore (Fig.48 - 49).
Fig.50 - 51 show the before and after shots.
To see more by Daniel Bystedt, check out ZBrush Characters & Creatures