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Learning the two rules of flattening

From: Illustrator Insider Training: Seeing Through Transparency

Video: Learning the two rules of flattening

So we understand this concept of transparency flattening. But let's take a closer look and find out exactly what this process actually is. How does this file actually go through this process of transparency flattening? Not only we will get a better understanding of exactly what transparency flattening is, we'll learn to avoid potential problems later on in our workflow. Now I am looking at a document here called blueyellow2.ai. I have two shapes here. The yellow shape has the Multiply blend mode applied to it. So wherever that shape overlaps the blue, I now see green.

Learning the two rules of flattening

So we understand this concept of transparency flattening. But let's take a closer look and find out exactly what this process actually is. How does this file actually go through this process of transparency flattening? Not only we will get a better understanding of exactly what transparency flattening is, we'll learn to avoid potential problems later on in our workflow. Now I am looking at a document here called blueyellow2.ai. I have two shapes here. The yellow shape has the Multiply blend mode applied to it. So wherever that shape overlaps the blue, I now see green.

We already established that PostScript does not know how to print transparency. So when I print this to PostScript device, it's not going to know how to make that area green where the two objects overlap. So Illustrator now has to go through this flattening process, so that the PostScript printer can know what to print. Now, flattening itself actually happens in two stages, or I actually like to call them the two rules of flattening. The first rule is that Illustrator must remove all transparency commands, which is pretty straightforward, because obviously, if I'm printing to a PostScript device and the PostScript device does not know what transparency is, I can't be in a state where I am sending transparency commands to my printer.

So before this gets to my printer, I have to completely remove all of the transparency settings. However, if I were to simply take this shape right here, this yellow shape, and remove the transparency settings, meaning go over here to my Transparency panel and set the Multiply blend mode back to Normal, I'm going to find that that I'm actually changing the way that my artwork looks. In other words, I would be able to create something inside of Illustrator, see it one way on my screen, but when I printed it out, I would see something completely different on the sheet of paper.

We don't ever want to get into that kind of situation. We want to make sure that what I see on my screen and what I see that comes out of my printer look exactly the same. So that's where the second rule of flattening comes into play. The second rule of flattening states that while I am removing the transparency from my artwork, I may not change the artwork's appearance. In other words, I have to find a way to both remove the transparency, and I'll press Undo here, yet make sure that it looks just like this after that transparency flattening process is done.

So again, the two rules of transparency are: one, remove all transparency, and then two, in that process of removing all the transparency, do not allow any changes to occur to the appearance of my artwork. Now obviously, something has to give and what gives is the editability of my artwork. That's why after flattening is done, I see my artwork is chopped up into these multiple atomic regions. Now in this case here, I'm going to select both of these shapes right now and I'm going to go to choose Object > Flatten Transparency, so we could see the results of the transparency flattening.

I am left with these opaque objects. These are the atomic regions, but there is no longer any transparency inside of my document. So we can clearly see those two rules at play right now. Illustrator A, got rid of all my transparency, and then B, it preserved the appearance of my artwork. Even though it had to chop apart my artwork to get that appearance to look the same, that is always going to be the key. Illustrator will always choose to preserve the visual appearance of my artwork and sacrifice the editability of my artwork in order to accomplish that.

Now this is a very simple and straightforward case. I started out with two vector objects and ended up with three vector objects. So that really is not so bad. I'm going to press Undo one more time. I'm now back to the state before this file was flattened. If I now take my Direct Selection tool and I take this yellow shape, I can see I can still move it around and get that nice green overlapping area. But now I'm going to do something little bit different. I'm going to take the blue shape right here and I'm going to changes its fill color to something else. Let me click over here on the Fill icon right here and change it to this little gradient over here called Purple2.

In fact, I'll take this yellow shape right here and I'll change that also to a gradient. Let me do this crazy gradient over here called Green, Yellow, Orange. Now I have these two gradients that are overlapping each other. On top of that, I'm going to go ahead now and show my Gradient panel and I'll change the Angle of this gradient to 45 degrees. So now let's take a closer look at our artwork over here. I have these two vector shapes. One is filled with a gradient, one is filled with a different gradient, and one of these gradients is actually rotated on a 45-degree angle.

So what happens now when I want to print this piece of artwork? Let's think about those two rules of flattening. We already know that I have to remove all the transparency in my file. So I'm going to end up with those three shapes that are kind of broken apart, right? But the middle shape over here that's going to be created now by that flattening process, what's going to be filled inside of that area? Well, right now that area visually is made up of two different gradients that are on top of each other and each of those gradients are going in different directions. One of those gradients is on 90 degree angle where one of them is on 45 degree angle.

So when Illustrator breaks apart now into three pieces, it can't really keep a gradient in that area there, because there is no way to accomplish an appearance that looks just like that in the world of PostScript. Sure, I can have gradients in the world of PostScript, but I can't have a gradient that travels in two different directions simultaneously in the same object. So that's where rule number two comes into play. Rule number two states that I'm not allowed to change the appearance of my artwork when I remove the transparency. So the only way for Illustrator to achieve that exact appearance is by actually rasterizing that artwork, filling that part of that object with an image, and you know what? That's exactly what happens.

Let's take a look at that. I'm going to take my Regular Selection tool here. I'll select two vector shapes, both filled with gradients. I'll go to the Object menu and I'll choose Flatten Transparency. I'll choose OK and now if I take a look now with my Direct Selection tool, I have one vector shape over here, I have another vector shape over here, but this shape right now has actually been rasterized. Notice over here in my Appearance panel, the artwork that I've just selected right now is an image and it's actually an image that's placed into a mask of that shape.

So if we think about it, when I set out to actually draw this Illustrator file, I didn't have any rasterized components inside of it. All I had was two vector shapes. However, my end result, what I'm going to get out of my printer, actually now is three shapes and one of the shapes has actually been rasterized. Now the first question you might ask yourself is, okay, I get it. It's an image now. But what resolution is that? Is that a high-resolution image? Is that a low-resolution image? I mean on some level, we never really thought about resolution at all inside of Illustrator.

After all, we've always been taught that Illustrator artwork is always infinitely scalable. We've just seen that obviously that's not the case. We'll actually learn in detail how to control the resolution of this type of artwork a little bit later on inside of this chapter. However, I want to bring up this point. It's important to realize that Illustrator in this case had absolutely no choice but to rasterize that area. By overlapping these gradients that were traveling in different directions, the only way for Illustrator to achieve that appearance was to rasterize that area.

That's the length that Illustrator goes to, to ensure that it doesn't break that rule number two. That it does not change the appearance of my artwork when my file is flattened. So in this example here, Illustrator just had no recourse. The only way that I can possibly print this kind of artwork on a PostScript device would be to rasterize that middle area. However, what if I told you that sometimes Illustrator will rasterize artwork because it feels like it. Maybe it's just not in the mood of keeping things vector. As crazy as that sounds, that actually can happen inside of Illustrator. How? We'll cover that in the next movie.

Show transcript

This video is part of

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  1. 7m 4s
    1. Welcome
      1m 6s
    2. The history of vector transparency
      4m 2s
    3. Getting the most out of this training
      1m 30s
    4. Using the exercise files
      26s
  2. 6m 21s
    1. Transparency living in a world of PostScript
      2m 56s
    2. Transparency...it's everywhere
      2m 13s
    3. Transparency across Adobe applications
      1m 12s
  3. 42m 20s
    1. Deconstructing the Transparency panel
      7m 48s
    2. Adding transparency to gradients
      4m 59s
    3. Using the Isolate Blending setting
      5m 20s
    4. Understanding how overprints and knockouts work
      6m 26s
    5. Using the Knockout Group setting
      6m 47s
    6. Using the Knockout Group setting without a group
      6m 2s
    7. Understanding the Opacity & Mask Define Knockout Shape setting
      4m 58s
  4. 36m 26s
    1. What is an opacity mask?
      3m 37s
    2. Learning from channels in Photoshop
      7m 20s
    3. Creating an opacity mask
      6m 44s
    4. Editing an opacity mask
      5m 31s
    5. Using a gradient as an opacity mask
      4m 44s
    6. Using image pixels as an opacity mask
      4m 4s
    7. Using a complex appearance as an opacity mask
      4m 26s
  5. 53m 30s
    1. Understanding transparency flattening
      5m 58s
    2. Learning the two rules of flattening
      8m 1s
    3. Understanding the concept of complex regions
      7m 47s
    4. Exploring the Transparency Flattener options
      11m 44s
    5. The relationship between flattening and stacking order
      8m 22s
    6. Using the Flattener Preview panel
      8m 3s
    7. Creating and sharing flattener presets
      3m 35s
  6. 24m 37s
    1. Working with PostScript (EPS) files
      7m 22s
    2. Placing Illustrator files into InDesign layouts
      3m 59s
    3. Copying graphics from Illustrator
      2m 41s
    4. Saving PDF files
      4m 41s
    5. Using the PDF/X standards
      4m 36s
    6. Printing files from Illustrator
      1m 18s
  7. 34s
    1. Next steps
      34s

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