Working with Tools in Paint Shop Pro 8 - Difference Blend Mode, Dodge and Burn (Page 6 of 16 ) Difference is a blend mode you use to create special effects rather than to create a photorealistic look. Using a different math formula altogether, Difference subtracts the color value of the blend color from that of the base color. But the result isn't necessarily what common sense tells you it might be. The purpose of Difference is not only to subtract color values from one another, but to create a new and altogether different color wherever the two blended colors differ the most. To accomplish this, the blend color values—R, G, and B—are subtracted from the base color values. When the result dips below zero (because negative values can't be represented on the RGB scale), the sign of the number is removed. As a result, if you subtract more red from the base color than it actually has, at some point below zero, the result color will start gaining red. In the sample, you'll see some interesting results using Difference mode. The light-yellow stripe is now light-to-dark green; the blue stripe blends from purple to yellow-brown; the green stripe becomes red to light-purple. 
Figure 3.15 Difference blend mode. Consider these rules when working with Difference blend mode: First, black is considered "zero," and subtracting zero from anything leaves you with what you had to begin with. Second, subtracting a color from itself results in black. Third, subtracting double a color's value results in that same value, so medium gray minus white equals medium gray. If you place an all white layer below a layer using Difference mode, you will get a negative image—roughly the same effect you will get if you choose Adjust, Negative Image (to invert the colors in current layer) or Layers, New Adjustment Layer, Invert (to add an adjustment layer which only inverts the colors of the layers below it). Dodge blend mode is named for a term used in photographic developing, where selected portions of a print are masked to block the light during exposure, causing the developed image to be lighter in those areas. In PSP, Dodge blend mode can simulate the effects of underexposure by lightening the base color. Dodge lightens the base colors using the lightness values of the blend colors. In the sample, you can see that the light-yellow stripe has been totally burned out of color by Dodge mode. The medium-blue stripe manages to retain a bit of its blended purple color, while the dark-green stripe (which, when blended with red, becomes brownish) manages to hang onto most of its color. 
Figure 3.16 Dodge blend mode. In practice, Dodge works best when the blend color is darker than the base color. When the blend color is lighter, Dodge can actually burn out most colors, turning them white. This blend mode's best use is for bleaching areas of a photograph. Burn blend mode was so named because burning is the opposite technique of dodging in photo developing: It increases exposure in certain areas to darken the print. Burn mode darkens the base colors using the reverse-lightness values of the blend color. A dark or medium-dark blend color has the effect of darkening, or even blackening, the base color; while a lighter blend color lightens the base color and might even replace it a bit. In our sample, the very light stripe darkens the gradient layer just a bit; the dark-green stripe darkens the gradient layer by quite a lot. 
Figure 3.17 Burn blend mode. Exclusion blend mode is the closest mode to a "negative" that PSP offers. It works like Difference mode, blending the base color with the blend color to create a color that's exactly halfway between the two on the color scale. Exclusion then uses the exact opposite of the lightness value of the blend color to darken the base color. If you use a light blend color, you'll darken the base color by quite a bit more than if you use a medium blend color. To create a negative for a photograph, add a blend layer filled with a light color (for interesting color effects), or pure white (for a more normal negative look). On the sample, each stripe becomes the color of its opposite, and much darker or lighter than the gradient below. 
Figure 3.18 Exclusion blend mode.  This chapter is from Paint Shop Pro 8, by Jennifer Fulton, (Sams, 2004, ISBN: 0672323893). Check it out at your favorite bookstore today.
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