Difference, Exclusion, Subtract, and Divide

In this exercise I will introduce you to the two Inversion modes, Difference and Exclusion, as well as the two Cancellation modes, Subtract and Divide. I am working inside of familiar looking file called Leaf demo.psd found inside the 07_inversion folder. In addition to the leaves in the background, I have got this full width gradient layer in the foreground, I am going to go ahead and click on it to select it. And then, let's switch it to the first of the modes, which is Difference. Now what happens with difference is that anything that's black in the active layer, does not invert the layers below at all, and anything that's white, inverts absolutely.

And so we end up with this gradient inversion with the gray values in-between inverting to different degrees. Now the great thing about difference, vis -?-vis, the other modes in this set, is that it's the final member of the Fill Opacity eight. So notice if I press the 5 key to reduce the opacity of his layer to 50%, we end up getting a pretty rotten effect here. So I will go ahead and press 0 in order to reset the Opacity to 100% and then I will press Shift+5 to reduce the Fill Opacity value to 50% and you can see that we get a completely different effect.

All right, I am going to press Shift+ 0 in order to restore fill to 100%. Now let's check out the next mode which is Exclusion, I will press Shift++, in order to advance to that mode. Black still does not invert, as you see over here on the left hand side. White inverts absolutely, as you can see on the right hand side, but the gray values end up muddying up the image and looking more or less opaque. Now I have to say, whereas the Difference mode is extremely useful, the Exclusion mode is more of a special effect that you may or may not find yourself applying.

Just to give you a sense here, I am going to turnoff that gradient layer for a moment and I am going to turn on this dummy layer and click on it. And this is just a blank brightness contrast adjustment layer, it's not doing anything. But, whereas here I had to change the Blend Mode to Difference, which I can do from the keyboard, by pressing Shift +Alt+E or Shift+Option+E on a Mac. Notice that the image ends up completely canceling itself out and while that might not seem like such a great thing, it's extremely useful as we'll see starting in the next exercise. Whereas, if I press Shift++ to advance to the Exclusion Mode, we end up getting all kinds of colorful interactions.

With the red leaves basically remaining intact and the yellowish leaves inverting to become blue and green and cyan, and so forth, so just to give you a sense of how these modes behave. All right, I am going to go ahead and turn off that dummy layer, turn on the Gradient layer once again and click on it. And now I will advance to the next mode by pressing Shift++, which is Subtract. And when you are subtracting black from an image, it ends up doing nothing, so you can see over here on the left-hand side the luminance levels of leaves are fairly intact.

When you subtract white however, you end up subtracting the brightest luminance level there is, and so everything ends up conversely going to black. I what you do know subtract and divide have some problems where straightforward compositing is concerned because they are beat by some other modes that we've already seen. I am going to switchover to this file that's called For comparison.psd and I am going to turn onto its gradient, it's the exact same gradient we saw a moment ago, the exact same leaves as well, and I am switch to the Darken blend mode that employs some traction, which is Linear Burn.

And notice this time we end up with blackness over here on the left hand side and unmodified leaves over on the right hand side. And I will press the Escape key to deactivate the Blend Mode for a moment, if I were to take that layer and invert it by pressing Ctrl+I or Command+I on the Mac. Now I will switch back to the other image where that gradient is affected by the Subtract mode and you can see that we end up achieving exactly the same effect. Here is subtract, and here is that same layer inverted, set to Linear Burn.

The big difference is that Linear Burn is part of the Fill Opacity eight, so if I press Shift+5 in order to reduce the Fill value to 50%, we end up getting a more gradual darkening effect over here in right hand side. If I switch back to Leaf demo file where I've applied the Subtract mode and I press Shift+5, we get a completely different effect, and that's because Fill and Opacity affect the Subtract mode in exactly the same way. So there's really no advantage to using the Subtract mode when you already have the Linear Burn mode at your disposal and it's a more powerful Blend Mode.

All right I am going to press Shift+0 to increase the Fill value back to 100% and I'm going to advance to the second cancellation mode, which is Divide. Notice this time we are ending up clipping the left-hand portion of the image to white. And those of you who are stuck with me for Chapter 2, you may recall that just as multiplying luminous levels darkens them, Divide ends up brightening them. However, whereas Multiply does not clip colors, the Divide mode does, and especially when we are dividing by the darker colors.

We end up dividing by these very small numbers, and so things brighten up tremendously, and of course, when you divide by Black which is zero, you get an undefined number, and that just goes to the roof. So we end up with this effect here. Again, Divide is already taking care of by one of the Lighten modes. And let me show you what that looks like. I will go ahead and switch back to this Comparative file, and I will restore the Fill value to 100% by pressing Shift+0. Now if I press Shift+Alt+N or Shift+ Option+N on the Mac you may recall we are working with an inverted version of the gradient.

So it's already inverted. Now if I go ahead and switch to this Inverted gradient to color dodge, switch back to the other file, and you can see that Divide is exactly the same as inverting the active layer and applying color dodge. Once again though, color dodge is part of the Fill Opacity eight, so if I press Shift+5 to reduce the Fill value to 50 %, I am going to restore a lot of the detail on the left-hand side of this image. If I switchover to Leaf demo file, where I've apply Divide to this opposite gradient, and I press Shift+5 to reduce the Fill value, we end up with this fairly hideous effect here.

And again, that's because Divide is not part of the Fill Opacity eight, so both the Fill and Opacity value is affected in exactly the same way. So again, Subtract and Divide are already taking care of by Linear Burn and Color Dodge respectively, and the job is done better by those Blend Modes. Meanwhile, Exclusion is kind of a weird freaky mode, Difference is the mode that's truly useful, and I'll show you why in the next exercise.