Select the image layer you want to sharpen paint on.
Choose Paint > Effect Brush > Sharpen Brush . To set the amount of sharpening, open the Brush Options window (for example, choose Paint > Effect Brush > Sharpen Brush ) and adjust the Sharpness from 0 (no sharpening) to 10 (maximum sharpening). To set the extent that each pixel is sharpened, set the Sharpen Strength from 0 to 4.
Drag the stylus on the area of the image layer you want to sharpen.
You can use any brush as a sharpen brush by setting Brush Mode to Sharpen in the Brush Options window.