Difference

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Original image.

When white is the blend color, the result is the same as inverting the image.

Using Difference

You already know that Difference produces black if you use it to blend a photograph with a copy of itself But something interesting happens once you invert the blend layer I find it easier to think of what happens to the original's tones when the image becomes a negative:

• The original's highlights become almost black in the blend layer, so they are darker but still show through

• The original's shadows become bright, almost white in the blend layer, so they are inverted

• Midtones are darkened because the difference between the positive and negative versions is small

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Difference Opacity

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Difference + White

Difference + White

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Difference + invert

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The original's highlights are darkened, shadows are lifted, and midtones become blacks.

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Dlf^rence

Difference is one of two comparative blending modes—the other being Exclusion. Both of these blending modes examine the difference between the base and blend color values. One of the easiest modes to understand, for each channel Difference outputs the difference between the blend and the base color. If the base and blend colors are identical, the difference is obviously o and the output color is black. Black is the neutral color, while blending with white inverts the image.

KEYBOARD SHORTCUT

Windows: Alt+Shift+E Mac: Option+Shift+E

Original image.

When white is the blend color, the result is the same as inverting the image.

Multiple Difference layers

Instead of inverting the blend layer, try adding a little blur This will work best on an image with plenty of detail As the difference between the two layers grows around high-contrast edges, a line drawing begins to emerge from the black With more blur, the line drawing becomes more like a halo and the image becomes brighter overall It will still be rather gloomy, though, so it's often worth experimenting with inverting the blend layer or adding multiple inverted and blurred copies

A little blur can reveal a line drawing from the black Difference self-blend.

Sometimes I use Difference to quickly review the effect of editing a picture With the original and edited versions as layers in the same image window, I hit Alt/Option-Shift-E and flick the top layer's blend mode to Difference Now that the edits are visible, I can zoom in and hit Alt/Option-Shift-N to restore the Normal blend mode and compare the detailed edits by toggling the layer's visibility by clicking on the eye icon.

Another use for Difference is to help join two layers manually—such as when you need to make two scans of a photograph that's too large to fit on your flatbed scanner Switch the top layer's blending mode to Difference and then start nudging it into place When they align perfectly, there will be no difference between the two layers' pixels and the matched overlap will appear black

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Difference

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Difference + Invert

Difference difference + invert + blur

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I'm not sure I like how this looks, but you can see the possibilities of stacking various combinations of Difference blend mode layers.

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