Technique: Tonal Separation

Yesterday I had posted about making some prints and, following that, noted I wanted to refine one image further (the Versailles stairwell).  Sat down with some coffee this morning to do just that, and figured I would post a quick how-to.  Never done this before so in the spirit of giving…

Most would agree that a wide range of distinct tones contribute to a quality black and white image (content aside).  The wall along the stairwell in my photo from Versailles has lots of texture among the stonework that wasn’t popping enough.  For this particular image I did the B&W conversion in Lightroom, but it’s local adjustment capabilities are limited so off to Photoshop we go.

Step 1: Selecting the Wall

I don’t want to adjust the whole image, just the wall along the stairs.  To do that I first need to make a selection.  Using the pen tool I run around the railing, across the stairs, and up along the wall.  After converting the path to a selection and creating a new Curves adjustment layer the resulting selection looks like this…

This is why I prefer creating the selection before adding the adjustment layer – the mask is created automatically.  On the left side is the resulting mask (the Pen tool rules).  Problem is that it’s a perfectly sharp edge and so the transition between the affected and unaffected areas in the image will be too obvious.  Quick solution – use the Feather control in the adjustment layers Properties panel to soften things up.  Just enough to blend the transition; too much of a feather will bleed the adjustment out too far.  Great thing about starting with a hard edge and then feathering here is that it is completely non-destructive.  I can go back and change any time I want.  With this mask in place I can proceed with my adjustment.  The mask will protect all areas in black (black conceals) and limit the adjustment to the white areas (white reveals).  The feathered transition area is a range of grays from light to dark which creates a blended adjustment falloff from full to nothing.

Step 2: Separating the Tones

Tonal separation is created by contrast between adjacent tones.  No contrast, no difference in tonal values, and you have a flat featureless surface.  To reveal texture you need to increase the difference between lights and darks.  The curves tool is the perfect animal for such a move as it:

1. Allows you to protect certain tones by locking them in place
2. Allows total precision in which tone you want to move

In this case I have locked down the darkest values (the pins on the bottom left of the curve).  Using the targeted adjustment tool (the finger) I slightly boost the lighter tones and drop the darker adjacent tones.  The steeper the curve, the more contrast.  Now there is a greater difference in value across the tones in the wall, and there’s more of a glow from the light.  Because I locked the darkest tones in place they don’t get too murky.  This includes the stair railing that, while included within the selection, doesn’t change.

Step 3: Cleanup

Since I’m in Photoshop already I might as well make a couple of other refinements.  This image was shot in low light with a DSLR (Nikon D300) that was good in its day for high ISO, but still produced its share of noise.  This becomes exaggerated with the weight of post-processing involved in a black and white conversion.  Grain, in my opinion, has a certain organic vibe in a black & white print which I like.  But the white speckles in the darkest area on the left are a bit too much.  No chance am I going to screw around spotting each of those bits, and noise reduction will just mush things up.

I have a better solution.  If you look close you’ll quickly see those speckles are little more than pixels in size.  Because they are light, and the surrounding area is dark, I can make use of Photoshop’s layer blending modes to render them almost invisible.

Merge up the background image and adjustment layer into a composite layer (Shift+Command+Option+E).  This creates a duplicate at the top of the stack.  Change the blend mode of that layer to Darken.  Nothing happens.  But if you activate the Move tool and nudge the layer once up and once to the right the grain magically disappears.  Why?  Because the blend mode causes the top layer to affect only pixels below it that are lighter in tone.  The surrounding darkness covers up the light sparkles on a pixel-by-pixel basis.  This of course affects the entire image which I don’t want, so I create a selection as above and then apply a mask to the top layer (along with a slight feather from the Properties panel) to isolate just that inside area to the left of the stairs.  At 100% the correction was a bit too strong so I backed off the opacity a bit and ended up at 40%.  I can go back and adjust this at any point if necessary.

Step 4: Adding a Vignette

Looking at the image further I decided the top, bottom, and left edges were still too light.  Burning them in helps keep attention on the stairs and wall.  For a quick vignette I employ my favorite, completely non-destructive and infinitely adjustable layer mask technique that involves the following:

1. Create a selection with the rectangular Marquee tool to identify where I want the vignette to lie
2. Add a new adjustment layer (doesn’t really matter which, although I generally use Curves)
3. Change adjustment layer blending mode to Multiply (darkens the image)
4. Invert and feather mask
5. Adjust opacity to taste

Here is what the result looks like:

The marquee selection leaves just the top, bottom, and left edges of the frame exposed as that’s where I want to burn.  The right edge is left alone.  The resulting mask when adding an adjustment layer (middle, above) is clearly too sharp and so a heavy dose of feathering (about 150px in this case) smooths the transition.  How does this look on the actual image?

Pretty nasty, non?  Obvious problem in the first image when the mask/adjustment layer first created is the burning is in the wrong place!  We want the edges darker, not the middle.  That’s because my initial selection included the middle and excluded the edges.  No probs.  With the layer mask selected simply inversing the mask (Command+I) turns black-to-white and white-to-black.  The “exposed” (white) area is now on the edges where it belongs.  That hard transition point is clearly obvious but is quickly rectified with the feather.  And bringing the effect down to 50% opacity keeps it from being too extreme (this value will vary by taste and image).  You could go back to the mask and selectively paint other areas in or out, or you can use the Transform tool on the mask to push/pull in the edges to fine tune.

Final Comparison

Below is a before/after comparison showing how the local tonal adjustment and edge burning add a bit more pop to the image.  The grain reduction is less obvious and won’t really show itself outside of larger prints.  This sounds like a lot of work but in reality took a fraction of the time compared to writing this post.  It gets faster and easier over time but the little things end up making a pretty big difference.