All this talk about Blend Modes earlier in this thread. came across a useful list of different modes and their capabilities (mainly as layer blend modes). They may be worth printing and keeping available.
Normal Edits or paints each pixel to make it the result color. This is the default mode. (Normal mode is called Threshold when you’re working with an image in bitmap or indexed-color mode.)
Dissolve Edits or paints each pixel to make it the result color. However, the result color is a random replacement of the pixels with the base color or the blend color, depending on the opacity at any pixel location. This mode works best with the brush tool and a large brush.
Behind Edits or paints only on the transparent part of a layer. This mode works only on layers with Lock Transparency deselected, and is analogous to painting on the back of transparent areas on a sheet of glass.
Clear Edits or paints each pixel and makes it transparent. (You'll see 'through' to what's on the layer underneath). You must be on a layer with Lock Transparency deselected in the Layers palette to use this mode.
Darken Looks at the color information in each channel and selects the base or blend color—whichever is darker—as the result color. Pixels lighter than the blend color are replaced, and pixels darker than the blend color do not change. [I found this useful when used with the Clone Stamp tool, in conjunction with Lighten - it means a bit of chopping and changing but it seems very good and you don't end up stamping a light shade onto a dark one, or vice versa, by mistake].
Multiply Looks at the color information in each channel and multiplies the base color by the blend color. The result color is always a darker color. Multiplying any color by black produces black. Multiplying any color by white leaves the color unchanged. When you’re painting with a color other than black or white, successive strokes with a painting tool produce progressively darker colors. The effect is similar to drawing on the image with multiple felt-tipped pens.
Color Burn Looks at the color information in each channel and darkens the base color to reflect the blend color. Blending with white produces no change.
Linear Burn Looks at the color information in each channel and darkens the base color to reflect the blend color by decreasing the brightness. Blending with white produces no change.
Lighten Looks at the color information in each channel and selects the base or blend color—whichever is lighter—as the result color. Pixels darker than the blend color are replaced, and pixels lighter than the blend color do not change.
Screen Looks at each channel’s color information and multiplies the inverse of the blend and base colors. The result color is always a lighter color. Screening with black leaves the color unchanged. Screening with white produces white. The effect is similar to projecting multiple photographic slides on top of each other.
Color Dodge Looks at the color information in each channel and brightens the base color to reflect the blend color. Blending with black produces no change.
Linear Dodge (Add) Looks at the color information in each channel and brightens the base color to reflect the blend color by increasing the brightness. Blending with black produces no change.
Lighter Color Compares the total of all channel values for the blend and base color and displays the higher value color. Does not produce a third color, which can result from the Lighten blend, because it chooses the highest channel values from both the base and blend color to create the result color.
Overlay Multiplies or screens the colors, depending on the base color. Patterns or colors overlay the existing pixels while preserving the highlights and shadows of the base color. The base color is mixed with the blend color to reflect the lightness or darkness of the original color.
Soft Light Darkens or lightens the colors, depending on the blend color. The effect is similar to shining a diffused spotlight on the image. If the blend color is lighter than 50% gray, the image is lightened. If the blend color is darker than 50% gray, the image is darkened. Painting with pure black or white produces a distinctly darker or lighter area but does not result in pure black or white.
Hard Light Multiplies or screens the colors, depending on the blend color. The effect is similar to shining a harsh spotlight on the image. If the blend color is lighter than 50% gray, the image is lightened. This is useful for adding highlights to an image. If the blend color is darker than 50% gray, the image is darkened. This is useful for adding shadows to an image. Painting with pure black or white results in pure black or white.
Vivid Light Burns or dodges the colors by increasing or decreasing the contrast, depending on the blend color. If the blend color (light source) is lighter than 50% gray, the image is lightened by decreasing the contrast. If the blend color is darker than 50% gray, the image is darkened by increasing the contrast.
Linear Light Burns or dodges the colors by decreasing or increasing the brightness, depending on the blend color. If the blend color (light source) is lighter than 50% gray, the image is lightened by increasing the brightness. If the blend color is darker than 50% gray, the image is darkened by decreasing the brightness.
Pin Light Replaces the colors, depending on the underblend color. If the blend color (light source) is lighter than 50% gray, pixels darker than the blend color are replaced, and pixels lighter than the blend color do not change. If the blend color is darker than 50% gray, pixels lighter than the blend color are replaced, and pixels darker than the blend color do not change. This mode is useful for adding special effects to an image.
Hard Mix Reduces colors to white, black, red, green, blue, yellow, cyan, and magenta—depending on the base color and the blend color.
Difference Looks at the color information in each channel and subtracts either the blend color from the base color or the base color from the blend color, depending on which has the greater brightness value. Blending with white inverts the base color values; blending with black produces no change.
Exclusion Creates an effect similar to, but lower in contrast, than the Difference mode. Blending with white inverts the base color values. Blending with black produces no change.
Hue Creates a result color with the luminance and saturation of the base color and the hue of the blend color.
Saturation Creates a result color with the luminance and hue of the base color and the saturation of the blend color. Painting with this mode in an area with zero saturation (a neutral gray area) causes no change.
Color Creates a result color with the luminance of the base color and the hue and saturation of the blend color. This preserves the gray levels in the image and is useful for coloring monochrome images and for tinting color images.
The principle for Blend Modes is the same across the board in all graphics software, as Adobe (and Aldus) more or less invented the rules and most other programs follow them. Don't forget the use of Brushes with Blend Modes.
I wish I could find something more graphic to explain all the above and, more importantly, some clues about when to use what, but it's worth having to hand. It's actually in the Help files.
