Now for the really fun stuff… make a new empty layer at the top of the layer stack. Then select Image-> Apply Image… from the menu bar at the top…
We are going to grab a copy of the b channel from the Lab document and put it into that empty layer. Set up the resulting dialog as shown…
The grayscale “b” channel has a unique tonal rendering that makes it especially well suited to applying it in Overlay blend mode…
This final Overlay blend darkens the sky and lightens the foreground even more! This dramatic improvement is not possible with any other combination of adjustments, and it all happens through blending of the different channels into the color image. Compare with the original raw adjusted version below:
At this point, we are done—I end up with a final Curve to set the white point & black point for the image, and call it a day.
I would be remiss if I didn’t point out one possible issue with regards to channel blending the red channel in RGB, with very saturated blue skies, using sRGB. Most natural looking photographic images work very well in sRGB, and gain no benefit from being in a larger gamut colorspace— this would include images with blue sky. However, the channel structure differences between ProPhoto RGB and sRGB are significant, and in some rare instances, ProPhoto RGB can mitigate tone compression problems with the 10-Channel Workflow blends. In our example image, looking at a detail of the sky – in color, no difference between sRGB and ProPhoto RGB…
In ProPhoto the red channel looks like this…
In sRGB the red channel looks like this…
There is a lot more contrast in the red channel here in sRGB and this is why it can be more powerfully dramatic, and somewhat problematic for channel blends that rely on the red channel, as in that first Channel Mixer luminosity move we used. ProPhoto RGB has a smoother red channel, and that can have some advantage in a channel blend maneuver. This advantage is not always obvious for blue sky images, and not advantageous at all for most other subjects. Portraits have a lighter red channel and so they don’t suffer from the red channel contrast defect in sRGB, and subjects with strong green content are also fine in sRGB, so most of the time sRGB is fine for this channel blending strategy. It is worth checking to see if you notice any posterizing around cloud edges in saturated blue skies after doing the red channel blend in sRGB—if so, try processing the image into ProPhoto RGB and doing your red channel blends there. Sky darkening effects won’t be as pronounced, but you are less likely to add posterization artifacts with particularly saturated blue skies.
I have a new online course: The 10-Channel Workflow – a comprehensive guide with 9 step-by-step projects with detailed video instruction, including downloadable work files for only $40. Click to learn how to enroll now.
I have a number of other color correction blog posts on my website that may also interest you –
- Color Correction for Best Skin Tone
- Desaturate Shadows for 3D Contrast
- Color to B&W and Beyond
- Evolution of a Glamour Photo
- 3D Tone Sculpting
- Luminosity Blending – part-1
- Luminosity Blending – part-2
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