Understanding the vector to raster journey

Vector graphic designers are constantly faced with a need to translate graphics from vector to raster with specific specifications for file format, resolution, and dimensions.

For example, I design Twitter cards and Facebook graphs in Illustrator, and I must adhere to the specs defined by Facebook and Twitter for PNG, GIF, or JPEG files. I also create infographics for technical print publications that have to be handed off in TIFF format. None of these formats (JPEG, GIF, PNG, or TIFF) are vector formats; they are raster (bitmap) formats. And, again, I have to not only adhere to the proper format but also meet different specs for image dimensions and resolution.

For an exploration of the differences between raster (bitmap) images and vector graphics, see Chapter 1.

Orchestrating vector to raster workflow

Let me share a couple essential tips on managing the process of exporting artwork to raster files:

• Be sure to save your files as Illustrator files. Do not just export them.
• Organize your graphics into artboards. Doing so allows you to batch-export graphics more quickly and easily. Later in the chapter, you walk through a scenario in which multiple graphics are exported together.

Defining raster dimensions

Defining an illustration’s size in a unit of measurement such as dots per inch (DPI) or pixels per inch (PPI) is usually not a critical or defining issue when working with pure vector graphics. Why not? Because vector graphics are infinitely scalable and don’t degrade even when reproduced at very large sizes. So whether a vector image is destined for a billboard or a palm card, the same Illustrator file can be used for both.

However, dimensions do matter when you export artwork to raster files. When you export to raster formats, you convert Illustrator’s define curves and fills into bunches of dots (for printers) or pixels (for screens). If you create a 1-inch square graphic, for example, with a resolution of 72 ppi (pixels per inch), that image will look fine if reproduced as a 1-inch square graphic on a screen with 72 dpi resolution. But the same image file will look awful when enlarged to a 10-inch square on that same screen.

I hate to get bogged down in math (grab your calculator at this point if it helps), but consider what happens when you turn a 1-inch-square, 72 ppi (or dpi in print terms) file over to a print designer who is creating a 300 dpi image. To maintain the integrity of the image, the print designer would have to reduce the image dimensions to less than ¼ inch. Or, if he uses the image as a 1-inch graphic, the resolution will degrade to less than 25 percent of the intended display.

In this scenario, it would have been appropriate to size the image at three times 72 pixels wide and high (216 pixels).

How do you know what resolution is appropriate for raster output for any particular project? And how do you set up your document to produce that resolution? The answer: Ask. Ask the team to whom you're handing over your graphic what resolution and image size they require.

Defining raster resolution

In Chapter 2, I explain how to define raster resolution when you create a document. In short, you choose File ⇒  New, click the More Settings button in the New Document dialog that opens, and select one of three options in the Raster Effects drop-down: 72 ppi, 150 ppi, or 300 ppi. This selection determines at which resolution the raster effect will be initially rendered.

That workflow usually works for print and screen projects, and allows you to easily apply one of three resolutions to raster output.

When you export a file to a raster format, however, you can specify any resolution, including 600 ppi. The details vary significantly depending on which raster format you export to, and which of Illustrator’s three output pathways you use, so I walk you through the details later in the sections of this chapter that zero in on exporting to PNG, JPEG, and TIFF files.

Exporting PNGs

Scenario: You're tasked with exporting a set of graphics to be used in advertisements for appliances targeted for Apple mobile devices. A web or app designer requires three versions of each graphic — low-resolution, medium-resolution, and high-resolution — to implement responsive design and match image resolution to different versions and screen resolutions of mobile Apple devices. High-resolution screens will display the highest resolution images, lower-resolution screens will display medium resolution images, and older smartphones and tablets will display the low-resolution version of the images. The images should have transparent backgrounds, so the background color or pattern of the web page shows through.

To batch-export a set of graphics as multiple-resolution PNGs, follow these steps:

1. Make sure each object is in an individual artboard, and the artboard is sized to fit the object. For the smoothest workflow, name each artboard with a name that will translate well into a web-compatible file name.

   Avoid spaces and special characters, except the underscore and hyphen, when naming the files. I explain how to define, name, and size artboards in Chapter 2. Your canvas should look something like the one in Figure 17-5.

   

2. Choose File ⇒ Export ⇒ Export for Screens and select the Artboards tab in the Export for Screens dialog.
3. In the Select section, click All.
4. In the Export To section of the dialog, navigate to a folder to which you will export the files.

5. To easily access the files after they're generated, select the Open Location after Export option.

   This option will open your operating system’s file manager with the exported files accessible.

6. To organize all the versions of the exported files into subfolders, select the Create Sub-folders option.

   Because I am creating three versions of each file, I am organizing them into subfolders to turn over to my web design team.

7. Use the Add Scale button in the Formats section to add different resolution outputs.

   In Figure 17-6, I added two additional resolutions, 2x for medium resolution screens and 3x for high resolution screens.

   The iOS (Apple mobile devices) and Android (mobile devices using the Android operating system) buttons in the Format section of the Export for Screens dialog automatically generate sets of output recommended for developers and designers targeting those respective environments.

   

8. To define anti-aliasing, interlacing, and transparency, click the gear icon (settings) in the Format section.
9. In the Format Settings dialog that opens, leave PNG set as the file format.
   • If you have type in your artwork, choosing Type Optimized (Hinted) will reduce jaggies that sometimes occur when type is converted to raster graphics.

   • To have graphics fade in from lower resolution to higher resolution in screens, rather than dropping in from top to bottom, select the Interlaced check box. I strongly recommend this option for all web graphics.

   • Transparent background color is the default selection, and allows the web page background to show through. Alternative options are to choose a white or black background, as shown in Figure 17-7.

10. Click Save Settings to return to the Export for Screens dialog, and then click the Export Artboard button.

    All artboards are exported into distinct folders for the low-resolution, medium-resolution (2x), and high-resolution (3x) versions of the PNG files. The files are ready to turn over to a web or app designer.

Optimizing JPEGS

Scenario: A client needs a file, small in dimensions and file size, to post at ETSY to promote her beautiful artwork. You will resize a large poster to a thumbnail-sized JPEG that will load quickly in any device, even with a poor Internet connection.

The Save for Web (Legacy) dialog is still here after being branded Legacy a few versions of Illustrator back because it's handy for specific tasks, especially fine-tuning JPEGs for export. The following steps guide you through the basic settings in that dialog:

1. Prepare your artwork for export to JPEG by making sure the artwork you're exporting is in a single, selected artboard.

   See details on placing artwork in an artboard and selecting an artboard in Chapter 2.

2. Choose File ⇒ Export ⇒ Save for Web (Legacy).

   The Save for Web dialog appears.

3. To compare before-and-after versions of your file, choose the 2-Up tab at the top of the dialog, and experiment with different compression settings:
   1. To avoid exporting objects that are not part of the illustration, select the Clip to Artboard check box.
   2. Because you're exporting to JPEG, select JPEG from the File drop-down.
   3. Select the Progressive check box so the exported image fades in instead of dropping down line by line as it loads in a browser.
   4. In the Image Size section of the dialog, enter the dimensions of the target output.
   5. If your image is mostly art, choose Art Optimized in the drop-down in the Image Size area of the dialog. If it's mostly Type, choose Type Optimized. If your artwork is equal parts type and art, choose None.
   6. Because JPEG images do not export with transparent backgrounds, choose a background color from the Matte drop-down.
   7. Use trial-and-error to see if the Browser Dither check box, which manages the transition from your artwork to the web page background, improves the appearance of the edges of your artwork.
   8. Experiment with different quality output by using the drop-down (with options ranging from Low to Maximum) or by entering percent values in the quality slider. As you adjust quality, note the output preview quality on the right side of the 2-Up screen and the output file size, as shown in Figure 17-8.
4. When you arrive at the optimal relationship between export quality (which you want to maximize) and file size (which you want to minimize for faster loading), click Save.
5. In the dialog that opens, navigate to a folder and choose Save again.

Handing off TIFF artwork to print

Scenario: You have designed a poster to be featured in a full-color commercially printed book using four-color printing. (For more on that process, see Chapter 2.) The publisher may want to have his or her own design team make some tweaks to the file, but the team isn’t Illustrator-fluent and works only in Photoshop. The publisher has specified that the file should be in desktop-publishing-friendly TIFF format. (File size is not an issue.)

The TIFF files are usually stored uncompressed, and because they aren’t downloaded into screens, file size usually isn’t an issue. Also, TIFF format files can store layers. TIFF images support printer-compatible CMYK.

Follow these steps to export artwork within one selected artboard to a TIFF file. (I explain how to place artwork in an artboard and select an artboard in Chapter 2.)

1. Choose File ⇒ Export ⇒ Export As, navigate to a folder, and enter a file name in the dialog that appears.
2. In the Format drop-down, choose TIFF (tif).

3. To not include stray objects or other artboards, select Use Artboards.

   If you have an artboard selected, 1 appears in the Range box.

4. Click Export to display the TIFF Options dialog, and choose a color model, resolution, anti-aliasing, and other options, as shown in Figure 17-9:
   • Color Model: Determines the color model of the exported file. In most cases, for commercial printing, that will be CMYK.
   • Resolution: Determines quality of the exported rasterized image. Higher resolution results in better quality.

   • Anti-Aliasing: Minimizes jagged edges in artwork but that is often not an issue for high-resolution print so unless your printer recommends this, don’t select it.

     LZW Compression: Reduces file size without reducing image quality. This process is lossless.

     Embed ICC Profile: Maintains color consistency between your screen and print output.

5. Click OK to save the file.