Blending Modes part 4: Darkening


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Doug
Blending Modes part 4: Darkening

The majority of the blending modes in LightZone result in somewhat darker images than Normal does.

To some extent, this is a side-effect of LightZone's using a linear color-space for editing. As you look at the charts below, you'll notice that on most of them, the magenta "no change" line crosses the diagonal reference line right at level 14, which is 1 Ev below maximum, or 50% gray. In other words, at the 50% point in the linear color space. This isn't the case for editors that work in a gamma-adjusted color space. The number of Evs above that intersection is equal to the gamma adjustment. So for LightZone's gamma=1, we get 1 Ev above that point. But for most editors, working in gamma=2.2, they get 2.2 Ev above that point, which means the crossover is at midtone (about 22% gray) in those editors.

Also, as I noted in part 3, all of LightZone's blending modes are channel-by-channel. Some of them can result in some dramatic color shifts. I'll comment on each one as it comes up.

The blending modes for darkening

These are approximately in order from least darkening to most darkening.

Darken

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

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

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

About the only place I've seen the Darken blending mode used is with USM sharpening. It prevents the bright haloes that are the most visually objectionable, and thus allows stronger sharpening or a larger radius to be used. The standard DSLR Sharpen style includes a USM sharpening tool with Darken blending mode selected.

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.

Soft Burn

This relatively useless blending mode replaces the tool's effect in the shadows with about 1 Ev of darkening.

Light Crafts says: "This blending mode is similar to the Color Burn blending mode except that the effect results in less saturation and contrast." I have no idea where Light Crafts got that description. It's very unhelpful, especially given that Soft Burn is the least powerful of the darkening blend modes, while Color Burn is the most powerful.

The shadows are darkened by almost 1 Ev and the tool has almost no effect in the shadows. In the midtones, the image is darkened by about 1/2 Ev and the effect of the tool is mainly visible on the "bright" side. In the highlights, the darkening effect of the tool is reduced by about half. There is increased contrast, and the brighter the result from the tool, the more the contrast is increased.

One problem with these modes is that the name is chosen with the idea that you're going to use a mask with it. Typically, "burn" is darkening of highlights, but Soft Burn darkens everything but the highlights. Also, the modes are generally designed for gamma=2.2, so that the transition level between "darken" and "tool" is a lot closer to midtone. I can't say that I've ever found a good use for Soft Burn.

Caution: 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, and especially when using a tool that is making significant changes in levels.

Soft Dodge

Now here's a surprise. A "dodge" mode is in the "darkening" section, and Soft Dodge is darker than Soft Burn. That comes back to that problem where the names were chosen for use with masks. This blending mode darkens the shadows and midtones, and reduces the tool's effect in the brightest highlights.

Light Crafts says: "This blending mode is a combination of both the Color Dodge and inverse Color Burn modes, but much smoother than either. The base colors are darkened slightly with very bright blend colors dodged in." Another unhelpful description, especially since there is no "inverse Color Burn" mode in LightZone. This description appears to have been lifted directly from Pegtop.

The shadows and midtones are darkened about 1 Ev, and the effect of the tool is reduced in the very brightest highlights. There is increased contrast through the midtones and highlights, but with some diminishing of the tool's effect with increased brightness, reaching "no effect" at pure white.

This is an excellent alternative blending mode for the Tone Mapper and Contrast Mask tools, for when you need a very strong effect. Unless you like the "heavy-HDR" look, expect to back the Opacity slider down and/or push the Gamma slider up.

This blending mode can add a dramatic high-contrast look when used with the proper tool. It'll take the shadows down fairly hard, so don't use it when you want to preserve detail in the shadows. On the other hand, one side-effect of darkening the shadows is a significant reduction of noise in the shadows. The darkening wouldn't be so wide-spread on the image except that in LightZone's linear editing color space, the crossover from "darken" to "reduced tool effect" is up at level 14 instead of close to midtone like it is on a typical gamma=2.2 editor.

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 behavior of this blending mode is fairly uniform, so color shifts shouldn't be a major concern in practice.

Soft Light

This blending mode makes a significant increase in contrast while reducing the effect of the tool.

Light Crafts says: "This blending mode 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, the image is lightened as if it were dodged; if the blend color is darker, the image is darkened as if it were burned in."

This blending mode applies a gamma of about 1.8 across most of the range, giving a dramatic increase in contrast but with the effectiveness of the tool cut in half. At the bright end, the gamma drops off and the effectiveness of the tool drops off until it reaches zero at pure white.

This is the standard blending mode for the Tone Mapper and Contrast Mask tools. It's designed to be used with a mask, and those are the only LightZone tools that natively produce a mask.

It can be used to increase the contrast of an image, usually with the Opacity reduced. However, the contrast roll-off in the brightest highlights is usually undesirable. The reduced Opacity also diminishes the effectiveness of the tool, which had already been cut in half.

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 behavior of this blending mode is fairly uniform, so color shifts shouldn't be a major concern in practice.

Hard Light

This blending mode is pretty much useless except when used with a mask, and it doesn't even work particularly well with the Tone Mapper and Contrast Mask tools. So it's pretty much useless, period.

Light Crafts says: "This blending mode multiplies or screens the colors, depending on the blend color. If the blend color is lighter than 50% gray, the color is lightened (screened); if the blend color is darker than 50% gray, the color is darkened (multiplied). This is useful for adding highlights or shadows to an image."

This blending mode applies a gamma of 2 across most of its range, but the gamma goes hinky in the midtones and highlights when the tool produces brighter pixels.

I don't know of any good use for this blending mode. It's really designed to be used with a mask in a gamma=2.2 editor, and even on Tone Mapper and Contrast Mask it gives weird results.

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, especially in the brighter areas. This can result in some unexpected color shifts.

Overlay

Although remarkably similar to Hard Light when you look at the charts, the Overlay blending mode turns out to be much more useful. As Pegtop notes, the names on Overlay and Hard Light are backwards. This is the "harder" version of Soft Light, and is primarily a contrast increase.

Light Crafts says: "Multiplies or screens the colors depending on the base color. Patterns or colors overlay existing pixels while preserving the highlights and shadows of the base color. The base color is not replaced, but is mixed with the blend color to reflect the relative lightness or darkness of the original color."

This blending mode applies a gamma of 2 across the entire range, without the hinkiness that Hard Light exhibits. This is a big increase in contrast. There is a drop-off in tool effectiveness in the brightest highlights, reaching zero effect at pure white.

This is an excellent alternative blending mode for the Tone Mapper and Contrast Mask tools, for when you need a stronger effect. In fact, the Overlay blending mode is what is usually recommended for contrast masking operations, although it generally needs a reduced Opacity setting.

The Overlay blending mode is useful for increasing contrast; the Opacity setting controls the contrast effect (but also controls the effectiveness of the tool). Overlay is a very close relative of Soft Light — the gamma is slightly higher and Overlay doesn't cut the tool's effectiveness in half the way that Soft Light does.

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 behavior of this blending mode is fairly uniform, so color shifts shouldn't be a major concern in practice.

Multiply

This blending mode darkens the entire image except for pure white, which is left alone.

Light Crafts says: "This blending mode multiplies the base and blend colors. The result color is always darker. The effect is similar to projecting multiple photographic slides onto the same screen." That last sentence is bizarre; it's lifted from Screen mode, which is a lightening blending mode.

This is a straight gamma 2.0 conversion, with everything below white being darkened.

The Multiply blending mode is a clean way to increase the overall contrast of an image, especially when used with a "do-nothing" tool — I personally grab the Hue/Saturation (HSL) tool. The Opacity control then becomes the contrast control.

This blending mode is applied on a channel-by-channel basis. Since this is a pure gamma function, the only color shifts should be in the brightest areas, on pixels in which one or two channels were maxed out so they're already shifted a bit. The maxed-out channels won't be affected in those pixels, but the other channels will be reduced. This could significantly increase the saturation of the existing yellow, cyan, or magenta tints in those pixels which have a single channel maxed out, or the existing red, green, or blue tints of those pixels with two channels maxed out.

Color Burn

This blending mode is simply crazy.

Light Crafts says: "Darkens the base color to reflect the blend color by increasing contrast." Increasing contrast? That's an understatement.

Does this chart look at all sane? Gammas run in the range of 10-15, and even the midtones are pushed down to black.

Color Burn is designed to be used with a mask, and it can used in a Tone Mapper (or Contrast Mask) tool to emphasize color variation. For example, if the subtle differences in greens in your foliage are too subtle, you might want to give this a try. Control the amount of color variation with the Opacity slider and use the Gamma slider to adjust the resulting brightness. Obviously(?), this is taking advantage of the noticeable color shifts that Color Burn exhibits.

Other than that, I don't know of any reasonable use for this blending mode. I imagine that it might be useful for some artistic purposes.

Caution: This blending mode is applied on a channel-by-channel basis. With the high gammas, any pixel that survives being turned black probably was partially blown out, and will almost certainly be shifted toward a saturated red, green, or blue. The varying gammas depending on the effect of the tool can give some significant color shifts, too.