Mixing B&W with local contrast
by eNoBlog on Nov.03, 2009, under Post-processing, Techniques
Lately I’ve been going back through some of my photos, trying to spot images that would work well in B&W. I ran across this previous reject (never delete rejects), and noticed how even though the haze washes out the background foliage and colors are rather dull under the early morning haze, there are actually quite a few dark tones against lighter ones.
Click for larger image
Would this work in B&W? The first step is to work with Channel mixer, emphasizing the red channel and bringing some green as well to play off against the earthy orange tones in the curves. Here I chose a mix that subtracts blue, so I can push red and green beyond 100 to emphasize these tones. The total adds up to 100%, though it doesn’t always need to be so. In this case it did, to avoid clipping, a possibility I opted to avoid by keeping a watchful eye on the histogram.
 Click for larger image |
 Click for larger image |
As you can see, the result has some appeal, but is a bit flat. This is not unexpected. The haze is reducing contrast, so we need to think about how to counteract this with some contrast of our own. Several approaches, such as Brightness/Contrast and Unsharpmask with a large radius and low strength are available, but one typical way to boost contrast is through a S-shaped curve where the shadows are darkened, and the highlights lightened, as shown below.
 Click for larger image |
 Click for larger image |
This produces good contrast overall, but note how the shadows (background foliage) and highlights (water foam) tend to blend together. A subtler approach involves use of smaller S-curves in the shadows, midtones and highlights, as shown below. This is one way to enhance local contrast, with not quite as much pop, but still separating detail through better contrast. Note in particular the water in the lower right hand corner, where this third version retains more detail and definition than either of the previous two.
 Click for larger image |
 Click for larger image |
It’s up to you how heavily you want to apply this effect. For my taste, moderation usually wins the day. In any case, Channel mixer and local contrast add up to a powerful one-two punch when converting your images to B&W.
Update: Check out this subsequent write-up for a technique to further improve on this approach.
November 3rd, 2009 on 6:04 am
Hi, I still think that NIK control points (Vivenza for PS, CNX2 already carries it bundled) are better to adjust all aspects of image locally. And it carries the color info of point in question, so that similar points change accordingly. It’s a wonderful tool for local contrast, saturation, etc, adjustments.
November 3rd, 2009 on 8:33 am
interesting thoughts. I have only recently started to experiment with the “Channel Mixer” mode. It seems to hold some promise of what I need. Thanks for the information.
bj
November 3rd, 2009 on 6:24 pm
Tks for this clear process. I’m just getting into doing B+W and this is very useful.
John