I discovered a trick that allows me a greater degree of control over B&W conversions in Photolab 3.
I’m used to the B&W conversions using Photoshop CS6’s Adobe Camera RAW (ACR). With a B&W conversion, you are allowed to adjust the luminance of the various colors (red, yellow, green, cyan, blue, and magenta) in the original image. The adjusted image is the one that is converted to B&W.
PL2 has a similar capability of adjusting the luminance of selected color ranges, but the conversion to B&W (under Style - Toning) occurs before the HSL control is processed; once the image is B&W, the HSL control no longer sees the colors in the image; HSL adjustments have no effect.
With PL3, I created a preset that only affects the new HSL control; what it does is set the saturation of each color to 0 (leaving everything else at default value). By applying the preset, my image becomes B&W; however, after the preset is applied, I can adjust the luminance of the individual colors.
This doesn’t work with PL2. Luminance and saturation are hooked together in some manner such that when saturation is 0, luminance changes do nothing.
One problem with this scheme is that, while it creates a B&W image, I don’t know that it does so in a manner that is compatible with the eye’s sensitivity (which is usually calculated as luminance = 30% of the red channel, 59% of the green and 11% of the blue). In addition to creating a preset with the saturation set to 0 for each color, it might also be necessary to adjust the color ranges and their luminosity. By working with some reference color image and its properly converted B&W equivalent, it might be possible to create an accurate B&W preset. In the end, this might simply reproduce the results of Style - Toning; B&W, but with the ability to tweak the conversion that is not otherwise possible.
The controls appear to be in the order of the color pipeline. For example, color changes from RAW White Balance are fed to Color Accentuation, then to Color Rendering, Style - Toning and finally HSL. Since HSL is after Style - Toning, B&W toning eliminates the colors HSL would affect. I suspect this was done because one might want to apply HSL adjustments for Style - Toning: Landscape or Style - Toning: Portrait. For Sepia toning, HSL adjustments aren’t that important, and putting B&W toning ahead of HSL is counter-productive.
The DxO people might have created a more flexible application simply by removing B&W from the toning operations and making it a toggle after HSL.