The relationship between flattening and stacking order
Video: The relationship between flattening and stacking orderThroughout this training title I've told you that if you're familiar with exactly what goes on during the flattening process, you can learn to anticipate potential issues and fix them before they start causing problems later in your workflow. In this movie we're going to see an exact example of that. Now we already know that Illustrator can rasterize content if it feels like it based on performance. But we also know that we can disable that level of rasterization so we don't really have to worry about it as long as we use our right flattener settings when we print our file.
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In this installment of Illustrator Insider Training, Mordy Golding shows experienced Illustrator users how to create transparency effects and ensure reliable printing results. This course reviews the history of vector transparency and covers features such as knockout groups, opacity masks, and transparency flattening. Mordy also shows how to establish a safe workflow when placing Illustrator graphics containing transparency in PostScript, PDF, and InDesign files. A free worksheet is included with the course.
- Understanding how transparency works across the Adobe applications
- Deconstructing the Transparency panel
- Adding transparency to gradients
- Understanding how overprints and knockouts work
- Using a gradient or complex appearance as an opacity mask
- The rules of transparency flattening
- Working with complex regions
- Understanding the relationship between flattening and stacking order
- Creating and sharing flattener presets
- Saving PDF files and using the PDF/X standards
The relationship between flattening and stacking order
Throughout this training title I've told you that if you're familiar with exactly what goes on during the flattening process, you can learn to anticipate potential issues and fix them before they start causing problems later in your workflow. In this movie we're going to see an exact example of that. Now we already know that Illustrator can rasterize content if it feels like it based on performance. But we also know that we can disable that level of rasterization so we don't really have to worry about it as long as we use our right flattener settings when we print our file.
But we also know that there are times when Illustrator simply has no choice at all but to rasterize content simply because of the way that the artwork itself is built, as we had discussed already in the past. We've seen if we have two overlapping gradients for example that travel in different directions, the only way for Illustrator to maintain that appearance is to go ahead and rasterize those overlapping areas. However, obviously if you kind of want to be proactive about your design, if for some reason you wanted to keep some content vector, you would just know to avoid building that kind of artwork.
Now, of course there are some times when you want to create some kind of artwork and you want to achieve a certain type of appearance and you know going into that artwork is going to be rasterized. But let's take a look at a different example. Let's talk about how we just build our artwork on a regular day-to-day basis. Often we don't pay that much attention to how our artwork is built, but as we're soon going to see the way that we build our artwork can also kind of predetermine how that artwork eventually is going to be flattened. Let's take a look at this example right here. It's called label.ai. It's just simply a label here that has a nice logo on it.
It has some text here, but let's take a closer look at the actual stacking order right here. I have this group over here, which are these flowers. You can see that over here inside of my Layers panel I have flowers here and then I have this word Seeds, which appears right over here. So notice that the word Seeds appears beneath the group flowers in the stacking order. Now the group itself has a soft shadow on it. Now we know that the soft drop shadow is an effect that's going to get rasterized. That's the only way to achieve that kind of an appearance.
However, since the object with the drop shadow was sitting at the top of the stacking order, all objects beneath that object are also going to be kind of included within that drop shadow. In other words, if I look right now at the drop shadow itself, which is going to have a bounding box of something like this for example, anything that falls beneath these objects and falls within that bounding area has to become part of the raster image that Illustrator is going to create for the drop shadow. So let's just be clear for a moment. The actual leaf itself right over here which sits on top of the drop shadow, I could leave that as a vector object.
However, the drop shadow that's beneath it is going to have to be merged with this gradient in the background. In other words, Illustrator is going to have to take not only the drop shadow, but also the background behind the drop shadow and combine them into a single image. Now since the text over here falls within the boundaries or I should say part of this text falls within the boundaries of this drop shadow, Illustrator is going to be forced to rasterize the text also. But Illustrator is smart. It doesn't rasterize everything. If you remember the example way back in the beginning when we spoke about just two overlapping shapes that are filled with gradients and that middle area became rasterized because that was the only way to actually display that artwork without changing its appearance, Illustrator didn't just give up and throw up its hands and say "Well, I'm just going to rasterize the whole thing." No, it only rasterized the part that it cannot recreate in vector form.
However, the other elements that were inside that illustration remained vector. So Illustrator really only goes ahead and rasterizes the content that it has to rasterize. So in this case over here, Illustrator sees that some of that text is not actually enclosed by that bounding area so it doesn't have to rasterize the whole text, which will actually leave us with something quite interesting and probably undesirable. It would mean that part of this text, at least the bottom part here, would remain crisp and vector, but I might see a little bit of boldness appear just in the top part of the d and at the top part of the capital S. In fact, in the final output it may look like something went wrong.
Even though according to my eye right now the drop shadow itself doesn't touch the S, the S still falls within that overall bounding area of that drop-shadow. Let's actually see this in action. I'm going to zoom in a little bit closer here and I'm also going to turn off the Color Block, the Organic Text, and also the Background, so we can just focus on these elements right here. I'm going to select these two groups right here, the group and the text. And remember right now in my stacking order the word Seeds appears beneath the drop shadow in the stacking order. I'll now go to Object and I'll choose Flatten Transparency and I'll choose my default settings here and take a look at what happened.
If I take my Direct Selection tool and I drag the word Seeds down here, the word Seeds still appears as regular text here because that was at the bottom of the stacking order and Illustrator did not need to rasterize all of it. However, that sits behind this image here and this image contains the top part of the S and the top part of the d. There's also an overall image that's over here as well. So Illustrator chopped this up and rasterized parts that it needed to and unfortunately part of my text got caught in that rasterized area simply because of where it was in the stacking order.
Let me back up a few steps here. I'm going to press Command+Z once and then twice or again that'll be Ctrl+Z on Windows. So now I'm back to the case here I have not yet flattened my transparency. But I know that this is going to now print and I know I want to avoid that odd rasterization to occur and actually eat up part of my text. So I can actually get around that by doing the following. I can go to my Layers panel. I can actually take the flowers group and drag it so that it appears beneath Seeds in the stacking order. So now my text appears above the drop shadow.
By doing this, Illustrator can actually now go ahead and rasterize that drop shadow and any background behind it, without having to involve the text in that type of function. So now if we go ahead and we take our regular Selection tool, we select these two elements and we choose Object and we choose Flatten Transparency, I'll use my default settings, you could see that now the text itself is no longer part of that rasterization. Illustrator went ahead and created one large raster for the drop shadow here in the background, but the text was actually left untouched, so I get clean sharp text in my result.
So as we can see here, if you pay close attention to how you build your artwork you can avoid odd-looking issues in your final printout when using transparency. The rule of thumb is always going to be to make sure that your text always sits at the top of the stacking order of your graphics. The way that I like to actually do this is I usually put all my text on a separate layer and I make sure that layer is always at the top of the stacking order of my document. Now I'll take a moment here to point out one other interesting fact.
You see when Illustrator 9 first came out and transparency was introduced to the world, stacking order was something that was not actually included in the flattener code, meaning that whenever Illustrator processed transparency it always looked at these overlapping areas and rasterize things as needed. But it never really understood if objects were above or below other objects in the stacking order. In other words, in the Illustrator 9 timeframe, even if your text was at the top of the stacking order, even if it was overlapping some other transparent object, that text would end up getting rasterized or partially rasterized.
It was only when Illustrator 10 came out that Adobe actually made the flattener code sensitive to stacking order, meaning it would first analyze where objects sat in the stacking order and then only chose to flatten and rasterize objects if it needed to. If there were elements at the top of the stacking order, the flattener knew to leave that alone. Again, that's one of the reasons why transparency got a bit of a bad rap when it first came out of the gate in Illustrator 9, because even if printers knew how to actually go ahead and change and modify their settings, there was simply no way to get around certain types of issues.
However, now with Illustrator and by the way, this applies also to InDesign if you're working with that application, as long as you make sure that your vector artwork sits on top of transparent artwork, it will never get rasterized or included in the rasterization process.
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