1. Convert your image to LAB mode. 2. Duplicate the layer, and name the lower one "L" (luminosity) and the upper one "C" (color). 3. Go to the channels studio for "L" and click on the "..." for AOpponent, and click "Clear". Do the same for BOpponent. 4. Go to the channels studio for "C" and click on the "..." for Lightness, and click "Clear" and then "Invert". 5. Change the blend mode for "C" to "Color". 6. Duplicate "L" and name the lower one "L blur", then apply a blur filter of your choice (Gaussian or median, etc.) to this layer. 7. Create a new group named "High pass" and place "L" inside it. Then, duplicate "L blur" and place it above "L" (inside the "High pass" group). 8. Go to the channels studio for the copy of "L blur" inside the "High pass" group, click the "..." for Lightness, and click "Invert". Set the blend opacity to 50% (blend mode normal). 9. Set the blend mode for the "High pass" group to linear light, and then rasterize the group if you wish.