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Saturate a photo using subtract mode

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The saturation of a color is determined by a combination of light intensity and how much it is distributed across the spectrum of different wavelengths.  The math for saturation includes luminosity. An interesting way to saturate a photo  is using the subtract blend mode.  This can be achieved by making a copy of the photo then inverting it.  This changes each color to the complementary color. But it also affects the luminosity.  You then apply the subtract blend mode. You are in essence subtracting the complementary colors from the original photo that has the effect of saturating the original color.  In RGB mode, when inverting, you not only invert the color but you also invert the luminosity.  This has will darken the photo colours.  So in practice what I have found you may need to change the brightness of the midtones and/or the shadows.  You can then apply blend ranges to apply the difference blend mode but I find keeping the highlights from the original works best.  

I have included a macro here that does this.  The macro lets you manipulate the brightness and contrast of the midtones and shadows if you wish.  YOU can also manipulate the blend range if you desire.  Have fun. Note that this works in the RGB color space but NOT in the LAB color space as the math is different.  

saturate by subtract RGB.afmacro

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I forgot to add that it is a single macro and has to be uploaded from the macro and not the macro library  pull down menu.

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