Blending Modes part 2: Lightening


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Doug
Blending Modes part 2: Lightening

The blending modes for lightening

A few blending modes generally result in the image being brighter than it was.

Lighten

This blending mode is pretty straightforward. For each pixel, the value produced by the tool is used if it's lighter than the original value.

Light Crafts says: "The result color is either the base or blend color, whichever is lighter."

Both the magenta (no change) and cyan (-1 Ev) lines lie right along the reference "original" line.

Caution: this blending mode is applied on a channel-by-channel basis. It's possible for a result pixel to have, for example, the red value produced by the tool while retaining the blue and green values from the original pixel. This can easily result in some unexpected color shifts.

Screen

This blending mode is intended to simulate both images simultaneously being projected on a screen.

Light Crafts says: "The result color is always lighter. The effect is similar to projecting multiple photographic slides onto the same screen."

At most brightness levels, the image is lightened by 1 Ev, and the effect of the tool is cut in half. In the brightest highlights, the amount of lightening drops off and the effect of the tool drops off toward zero.

This blending mode is applied on a channel-by-channel basis. It's possible for a pixel to be affected differently in, say, the red channel than in the blue channel. This can result in some unexpected color shifts. Fortunately, the fairly uniform behavior of this blending mode greatly reduces the chances of any color shifts being significant in practice.

Color Dodge

This blending mode lightens the highlights while leaving the shadows unchanged.

Light Crafts says: "Brightens the base color to reflect the blend color by decreasing contrast."

The lighter the original pixel, the more the result pixel is lightened. I don't understand the "decreasing contrast" explanation; the contrast is slightly increased through the upper midtones and lower highlights. However, the maximum output value is reached at a 50% input level (unless the tool produces a darker pixel), so clipping will occur in that top 1 Ev.

The Color Dodge blending mode can be used to really "amp up" the effect of the Tone Mapper and Contrast Mask tools. If you like the "heavy HDR" look, this is one way to get it. You'll probably need to increase the Gamma slider to keep things under control, and perhaps reduce the Opacity slider as well. You might want to try Soft Dodge first, though — it's not as severe.

This blending mode is applied on a channel-by-channel basis. It's possible for a pixel to be affected differently in, say, the red channel than in the blue channel. This can result in some unexpected color shifts, especially in colors that are both bright and somewhat saturated. Fortunately, the range of susceptible colors is fairly limited and the behavior of this blending mode is fairly uniform, so color shifts shouldn't be a major concern in practice.