Control shades and tone using Channels and blend modes for punchy black and white effects
Open your image and go to Layer>Duplicate Layer. In the pop-up box, set Document to New, and give it a name. Hit OK, and a copy of your image will open. Place it next to your original image, side by side in Photoshop.
On your original image, go to Image>Adjustments>Desaturate. This is a quick way to convert to black and white, without losing the brightness of your image, but important details can be lost in the main focal point, however, keep this version for later.
On the duplicate image, open the Channels palette and click on each RGB Channel separately. Choose the best Channel of the three where the main features of your subject (the eyes in our image) look at their best.
Ctrl/right-click your chosen Channel and select Duplicate. The same dialog pops-up as before, and in here select New under Document, and hit OK. This is our final version, and only Alpha 1 appears in the Channels palette.
Go to Image>Mode>Grayscale to make the background layer editable. Go into the Layers palette and drag the background layer onto the Create a New Layer button to create a copy in the palette.
With the duplicated layer selected, change the blend mode to Soft Light. This adds contrast and more punch to the black and white effect. If the effect is too strong, reduce the layer’s opacity to around 60%.
The eyes of our subject look perfect, but other areas seem to be bleached white due to the blend mode. Look at the original, desaturated version of your image and compare areas of details you want to add to the final version.
With the Move tool (V) drag and drop the original, desaturated version onto your final version while holding Shift to place it exactly over the top. Add a layer mask to its layer, Alt+click on the mask, and go to Image>Adjustments>Invert to make it black. Alt+click on the mask again to return to your image.
Select the Eraser tool and set the foreground colour to black. In the Options bar, make the Eraser’s Hardness 0%, choose a large brush size, and reduce its opacity to 20%. Paint over your image to bring the darker parts through containing the areas of detail.
Save your image and go to Layer>Flatten Image. To add further crispness to your black and white, go to Filter>Sharpen>Unsharp Mask. Apply this filter gently to avoid any glowing edges around subjects.