Here are a few things you need to understand about the differences between video and images for printing. Let me explain printing first.
Printing falls into two different categories. Digital printing uses inkjet printers that have to combine at least 4 different ink colors in a frequency modulated pattern to turn digital images and type into images on everything from paper to textiles, to glass. Offset printing separates full-color images into separate Cyan, Magenta, Yellow, and Black plates that are used together to transfer the CMYK ink to the paper anything else that can be run through a press. Offset Printing can also use separate Spot colors and some presses have more than just the four plates required to print color. Spot colors are used to accurately reproduce solid colors on things like Type, logos, and backgrounds.
For both types of printing (offset and digital) a color image is broken up into patterns. In offset printing, these separations are called halftone plates and they have line screen values. 80 to 85 line screen is typical for things like newspapers, higher quality line screen images for things like posters and magazines use line screens of 200 or more. Ink Jet printers and Laser printers use DPI or dots per inch. A 300 to 600 DPI printer can produce about the same quality image as an 85 line screen offset printer or the quality of a cheap newspaper.
Now let's talk about digital images and Illustrator files. Digital images, and video, and images for the web are all pixels. There is no DPI in a digital image. You can add metadata to a digital image that tells the printer how many pixels to put in an inch when it is printed, and page layout applications like Illustrator, In Design, or even MS Word will use that information to size images, but there is no way for a video app like After Effects to add PPI metadata to an image. A high-quality print from an offset printer or a digital printer is going to require the digital image to have somewhere between 200 and 300 pixels per inch. A low-quality print will require somewhere between 72 and 150 pixels per inch. More about this later.
I hope you get that. Now let's talk some numbers. If you know what size the final print is going to be and what kind of quality you want to achieve then you know how many pixels you need per inch being printed. It is also important to know the viewing distance.
Let's say you want to create an 8 X 10 print of your after effects composition that is high quality and looks like a good photograph when you hold it in your hand. If you want the image to be 10 inches wide then you are After Effects composition must be 10 inches X 300 pixels = 3000 pixels wide. If you just create a Photoshop file of a frame of your HD comp and you print it at 300 PPI the image will only be 6.4 inches by 3.6 inches.
If you want a standard 27 X 40-inch movie poster, you'll probably want somewhere between 150 and 200 for very high quality you just have to do the math. 40 inches times 150 PPI = 6000 pixels. That is a pretty big AE comp.
So that is the first step in preparing an AE comp for printing. When you work in Illustrator, and the file is sent to the printer, the vector art is filled with solid colors and the type remains vector art so it can be any size, but any images or effects like drop shadows and gradients must be set up using the appropriate PPI settings. Typically, for print, that is 300 in Illustrator, because it covers just about everything. If you are doing a billboard or sending the artwork to a newspaper you pick 72 to 150 in the Illustrator settings. After Effects cannot add vector information to an exported image, they are all pixels, so you can only send pixels.
By far the easiest and most efficient workflow is to set up the AE comp to the proper frame size, pick a frame, then use the Composition menu to Save the frame as Photoshop Layers. This will give you the most options in Photoshop. By default, if there is no PPI tag on an image file like the one After Effects created from your comp, Photoshop will assign 72 as the PPI for the image. All that is required to prepare that artwork for printing is to open up the image settings in Photoshop and change the PPI setting without resampling the image. Watch the image dimensions, if they change when you change the PPI then things are set up correctly. If the image dimensions do not change, then Photoshop will resample the image and change the number of pixels. You do not what that.
If the image is going to an Offset Press or it is going to someone to use in a page layout application, convert it to CMYK using the Image menu, then Save a Copy as a PSD or a TIFF or whatever format the printer or publisher requires. That is all there is to it. If the image is going to an inkjet or laser printer, you don't have to convert it to CMYK.
Color Management of CMYK images is handled at the PRESS. You don't have to worry about it. As long as your comp is the way you want it, you are done.
I hope this helps. I've been working with digital images and teaching After Effects for about 25 years and I can tell you that there are more people out there that don't understand the difference between DPI, PPI, and LIP than there are those who do. I've created images for billboards at 10 PPI and images for limited edition collector prints at 600 PPI, and preparing the artwork for all of them starts with knowing what size of the print and the viewing distance. High-resolution images have a lot of pixels and bit depth. High-quality printing has a sufficient number of dots (line screen) so that the image looks good at the normal viewing distance for that image. That's why billboards look great at 10 PPI, newspapers look ok at 72 PPI, and corporate brochures need to be around 300 to give the best impression.
Here's a link to a calculator that you may find useful: DPI: Movie poster One sheet Pay attention to the Print Pixel Size at the bottom. Remember - DPI is the printer setting. PPI is the tag you put on the frame you modified in the Photoshop file you created from your comp.
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