Adobe Illustrator: Exporting to the Correct Size & Raster Effects
Document Size, Resolution, and Flattening Transparency
I’ve been using Illustrator to create some textures. This involves applying live effects and blending modes – things that employ transparency. When you export to an image format, the effect’s transparency needs to ‘flattened’. This is where I ran into a color issue that took 2 days to figure out. Turns out my problem relates to how Illustrator defines a pixel and what happens to a live effect when its flattened. Here’s what I learned 🙂
Illustrator is for creating scalable vector graphics. SVG has no resolution – vectors can be scaled up or down with zero change in their appearance.
Vectors do take on a resolution once they need to be printed or exported to other formats like JPG and PNG.
I’m working on some textures for a print project. These are pretty big textures – at 100% scale I want them print as 12″ x 12″ at 300 dpi.
So I created a document with the settings below. I’ll pause now and say that my first mistake was thinking that the 300 dpi setting here controls the resolution files are exported at – it doesn’t. I explain what this setting IS for further down, but for now, ignore it.
Next, I created my texture using several live effects, expanded their appearance, and exported at 1x to PNG.
Looking at the file, the color was right but the dimensions were wrong – the file is 864 pixels x 864 pixels. In other words it’s 72 pixels per inch, which the printer will interpret as 72 dots per inch – nowhere near the 300 dpi I’m after.
So my next thought was to export the textures specifically at 300 dpi – this got me the right dimensions, but the color was wrong.
My next thought was to leave the live effects in place – skip expanding their appearance and go straight to exporting at 300 dpi. Again, I had the same color issue:
Pixels are Arbitrary
Illustrator uses 72 ppi as its base unit for export.
Turns out my problem was two-fold. First, I didn’t understand how Illustrator defines the abstract pixel and its relationship to physical measurements like the inch.
I work on projects for print and for web. I’ve always understood the concept of image resolution, and I’ll bet you do too.
Simply put, resolution is the amount of information/detail packed into a given unit of measurement.
In the print world, resolution is expressed as dots per inch or points per inch – this is a physical ratio tied to the printer’s capabilities, the dimensions of the print, and the level of detail in the source file.
If I want to print a 12″ x 12″ document at 300 dpi and have it look good, then my source file needs to have at least 3600 dots x 3600 dots of information (if not higher) and the printer needs to be capable of laying down 300 dots of ink per inch.
Common print resolutions are 150 dpi, 300 dpi, 1200 dpi, and any multiple of 144 dpi.
For the web, resolution is expressed as pixels per inch. Pixels are arbitrary & abstract – there are always 2.54 centimeters in an inch, but there can be any number of pixels in an inch.
Getting an image to look good on screen is about matching the image’s resolution to what the screen is capable of displaying.
On a desktop monitor in a browser, you’re generally seeing 72 pixels per inch. While there are screens capable of displaying much higher resolutions, 72 ppi is a standard web resolution and is Adobe Illustrator’s base resolution for exporting files.
An easy way to see that Illustrator uses 72 pixels per inch as its base unit is in the New Document dialog – set the document size to 72 pixels and then toggle the units selection.
From this you can see that 72 pixels = 72 points = 1 inch = 2.54 centimeters.
How to Get the Right Document Size
If your Illustrator file contains nothing but straight up vectors, then document size and resolution are essentially irrelevant – you can export vectors to any size and format and get what you expect.
But most Illustrator projects aren’t straight up vectors – quite often they contain live effects, blend modes, drop shadows, feathered & glowing edges, and other styles involving transparency.
When you print or export an AI file to a format that doesn’t support transparency, the file goes through a flattening process that produces a combination of vectors and rasterized areas.
These rasterized areas do have a resolution and this is where your document size and Illustrator’s default 72 ppi become relevant.
More on flattening in a moment. For now what’s important is that rasterized areas don’t scale the way vectors do. While it’s almost always okay to take a raster from a higher resolution to a lower one, you can’t start small and then go big – you’ll wind up with an image that’s blocky, blurred, and pixelated.
So it’s critical to start with a document size that will export at your intended resolution without needing to scale the raterized bits up.
Going back to the example of printing a 12″ x 12″ image at 300 dpi without scaling up, the document must have at least 3600 x 3600 dots or points or pixels – which Illustrator equates with 50 inches because its thinking in terms of 72 ppi / dpi.
Not too confusing, hu?
Resolution for Flattening Live Effects
As I said, my problem was two-fold. Once I got the correct document size for my intended export resolution, I had to set the correct resolution for flattening transparencies. Here again Illustrator defaults to 72 ppi and I need 300 ppi.
For this, Illustrator provides several presets plus the ability to define custom presets. The first place you’ll see these presets is in the New Document dialog – the setting I told you to ignore way back at the beginning.
If you missed this setting in the New Document dialog, you can change it at any time before flattening via File > Document Setup.
Another way to change this setting is via Effects > Document Raster Effects Settings.
You can view & manage presets via Edit > Transparency Flattener Presets.
And you can use Window > Flatten Preview to see which objects will be flattened and how different settings affect the outcome. This is a good way to explore the baked-in presets and tweak your own.
When to Flatten
Once the document size and raster settings are correct, you have to decide when to flatten.
The first option is to use Object > Expand Appearance to flatten the live Effects into a PNG. Often this is followed by doing an Image Trace to convert the PNG to vectors so it can be scaled without loss of quality.
The second option is to leave the Effects live & editable and allow the flattening to happen on export or print.
Since flattening is permanent – a.k.a. destructive – this should always be your first choice where possible.
My project is about creating textures for multiple uses. For this it makes sense to keeps a source file with the live Effects, export to a high resolution PNG, and then bring the PNG into projects as needed.
So why the color change that started this trek? On my first attempt I flattened the live Effects inta a PNG prior to exporting. Then I was scaling up during export – and we’ve all seen what happens when you try to make an image bigger.
What’s harder to understand is why this also happened when I exported with live Effects. Originally, I thought the export process would scale the Effects, but clearly this isn’t the case.
Here I have to accept that sometimes it’s okay to find a solution without ever fully understanding the issue.
I write these posts for my own benefit – 3 weeks from now I’ll forget and will need a day to figure it out all over again. If you’ve made it this far, thanks for stopping by & I hope it has helped you in some way 🙂