We have already introduced a good handful of sharpening methods. This is because there are more than a good handful of them; not just the well-known Unsharp Mask. You can also combine good old Unsharp Mask with other solutions, which produces a better result as using it in itself. For example, you can ignore color channels during sharpening.
Step 1: Open the photo
The point is to sharpen only the lightness information in the picture. Regarding the details, sharpening color channels is unnecessary.
Step 2: Switch the channel
First of all, switch from RGB Color to Lab Color mode. RGB stands for the red (R), green (G), and blue (B) channels. That is, all three are color channels. Lab mode provides two color channels (a and b) and a Lightness channel. The latter is what we need.
Step 3: Choose light!
Switch to the Channels palette and select the Lightness channel. You’ll see a monochrome picture showing the information in the selected channel. This is what you want to sharpen.
Step 4: As usual
Sharpen the picture as you would normally do, e.g. using Unsharp Mask. Because of tiny details, we specified a low Radius and a moderate Amount value. We left Threshold at 0. Set the values as you see fit for the particular picture.
Step 5: No surprise…
…that the result is much sharper. Only the lightness information, the details of the picture were sharpened. This way, color noise wasn’t increased—luminance noise, however, can grow by excessive sharpening.
300% zoom without sharpening300% zoom with sharpening