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The magic of InDesign's effects all happens via Adobe's transparency technology, which allows us to blend colors and detail from different objects. In order for it to all work there has to be a consistent color space for InDesign to use when it blends colors. This is called the transparency blend space and it's really important that you understand it in order to get the most out of InDesign's effects. Let's see how it works. So when we use transparency effects, InDesign compares different objects and combines their colors and detail. In order for objects to be blended, they have to be in the same color space.
So when you apply transparency, InDesign converts everything on a spread to the transparency blend space, regardless of whether that object is actually involved in the effect. And it's important to note that when I say things are converted, I don't mean that InDesign goes out and alters your Photoshop or Illustrator files; they are left completely alone. What I mean is that InDesign is using a different method for interpreting the colors in those files. It simulates as if you change the colors in those documents, just to give itself a reliable method for blending.
It's a totally nondestructive change. So let's see some of that change. Here I've a placed photo with a big flower and several small versions of the flower and I've overlaid each one with a blue swatch and I've set the blending mode to each of InDesign's 16 different blending modes. This one's set to the Normal blending mode and it completely knocks out the flower, and all the other ones blend with the flower. So they blend some aspect of that blue color with the color and detail of the flower photo underneath.
So you can see Multiply makes it darker, Screen makes it lighter, Overlay increases the contrast, so on and so forth, and things like Difference give you a really special effect, where it inverts the colors and mixed blues into orange and so forth. If I go up to my Edit menu and I choose Transparency Blend Space, I can see that this document is using Document RGB. So everything on this spread would be converted to RGB transparency blend space for the sake of this transparency effect. But if I choose Document CMYK, you'll see a change.
See that? Several of these different blending modes have a very different effect when we use Document CMYK, instead of Document RGB for our transparency blend space. I mean, for example, just look at that Difference blending mode. I'll switch back to RGB for a minute and keep an eye on that. So that's a pretty dramatic difference there. What exactly is going on? Well, we don't really want to get entirely into color management. That's a really deep topic but we can sort of explore a little bit using a utility that I have on the Mac called the ColorSync utility.
I'll switch over to that and one of the things I can do with the Mac's ColorSync utility is I can look at color profiles and I can look at RGB ones and compare them to CMYK ones to see the different colors I can represent in each color model. For example, I'll click on Adobe RGB and it gives me this graph of all the colors that can be represented in the Adobe RGB color space and it's a really neat thing because I can click and drag them around and it's a 3D map of the color space. So I can see all the dark colors by turning it upside down and I can see all the light colors by looking at the top, and I can spin it around and really get a sense of what colors are in Adobe RGB.
Now if I look at a different color profile like U.S. Web Coated (SWOP), I can see it has a much narrower range. Look at those reds and those greens, how far they got pulled in from the Adobe RGB space. What I can also do with this is I can compare the two different color spaces. So I'll switch back to Adobe and I'll click on this little triangle and I'll say Hold for comparison, and that's going to keep that on screen, and now I can click on a different color profile and compare the two. So I'll click on U.S. Web Coated (SWOP), and I can see the Adobe RGB ghosted around the outside of U.S. Web Coated (SWOP), and I can see the difference.
So the greens of Adobe RGB are way out here. I can represent all these kind of greens in Adobe RGB that I cannot make in U.S. Web Coated (SWOP). And when I switch to the Transparency Blend Space in InDesign, green colors that are out here will be converted to those colors down here, and that explains the color shift that we saw when we changed the Transparency Blend Space. Let's go back to InDesign and see some more of that. Again, I'll check my Transparency Blend Space and I'm using Document RGB.
Let's change that to Document CMYK. So now if I apply any transparency on this spread, everything on the spread will be converted to the Document CMYK blend space. So I'll just select this black square and go to my Effects panel and I'll just change the Opacity from 100% to 99%. And look at that. See all the color shift? That's really interesting because they're not even touching that black square. So you might not think they would be involved or have any kind of change with it. But just because they're on the same spread, InDesign will convert them to the transparency blend space.
So again, just like we saw in that ColorSync utility, the reds and the greens that were really rich and saturated in RGB are now kind of dulled and flattened when they are converted to the CMYK blend space. Let's try another example. Here are CMYK colors in a placed CMYK Photoshop file and I'll choose RGB blend space. So now these CMYK elements will be converted to RGB if there's any transparency on this spread. So again, I'll click the black square and I'll reduce the opacity to introduce transparency to the spread, and you didn't see very much of a change, and if you think back to that graph, that kind of makes sense because the RGB blend space has a much wider gamut of colors that it can represent.
So it can represent both those supersaturated reds and greens and these more dull reds and greens. So there's not going to be much of a change here. Now there is one more aspect to transparency blend space that's worth explaining. If I look in the menu, it just says, Document RGB and Document CMYK. Well, that doesn't really tell me exactly which flavor of RGB and CMYK I'm talking about. What is this document using for RGB and CMYK blend space? Well, I can look in my Color Settings and I can see my Working Spaces, but that's not necessarily the same as the document color spaces,and in fact, it's kind of annoying.
There's no real easy place to go to see which color spaces a document is using. These Working Spaces only apply to newly created documents, not necessarily documents you already have opened. So one way you can tell is by using either this North American Prepress 2 settings or your own custom settings, but just make sure you have this option checked, Profile Mismatches: Ask When Opening. That way if the RGB and CMYK working spaces are different from the Document CMYK and RGB working spaces, you'll get an alert.
Let me show you what I mean. I'll open another document that uses different RGB and CMYK spaces. This one called Profile Mismatch, and because I have that setting turned on, I get this dialog box and it will tell me the working spaces for that document. So in this case, this document is using Apple RGB as its document RGB space and U.S. Sheetfed Uncoated as its CMYK working space. So that's just a way you can know exactly which flavor of RGB and CMYK a document is using to blend with.
The color space you choose as your transparency blend space will determine a lot about the look of your effects. You can achieve a wider variety of effects using RGB blend space because some of the blending modes just work better there, but be mindful of what's happening when you apply transparency. Remember, everything on a spread is converted to the blend space. Keep an eye out for color shifts when you apply effects and know what color spaces your document is using. Make sure they are appropriate for your final output. That way you won't get any unexpected color changes at the end of your workflow.
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