Multiply and Screen – Enhance images tones and definition
The multiply and screen blending modes can be used to darken and lighten an image. The multiply blending darkens the image, the screen mode lightens the image. Along with darkening and lightening the image, the blending modes can be used to increase detail definition. The effect appears to sharpen the image though no actual sharpening is performed. When the multiply blending mode is used solely on the lighter tones it will darken those lighter tones along with increasing the detail definition those lighter areas. When the screen blending mode is used solely on the darker tones it will lighten those darker tones along with increasing the detail definition in those darker tones.
So as noted above it is important to chose the proper blending mode for desired effect; darken light tones or lighten dark tones. The challenge is that the entire image either darkens or lightens according to the blending mode chosen. To target and modify specific tones in the image, a mask can be used. A mask will allow the blending mode to penetrate and change the desired areas while leaving blocked areas unaffected. To pinpoint specific areas to be enhanced create a luminosity mask. Tony Kuyper Actions are wonderful resource for Luminosity Masks.
Though the blending mode and mask will enhance image tones there is potential for the loss of some detail in the modified areas. To improve the detail in those affected areas, the mask can be blurred using a Gaussian blur filter. How much blur is your personal choice. It is important to note that a mask should only be blurred when multiply blending mode is used on a light tones or screen blending mode is used on a dark tones otherwise you could inadvertently increasing the blur.
For more information about masking see Tony Kuyper’s website. His Luminosity Masks for Photoshop are an incredible resource. The techniques he uses to create luminosity masks will not only enhance your Photoshop knowledge but they will also improve your photography.