I need help downsizing my project

[Criizmeow]

Hello, im hoping someone with more experience in printing can help me. I have a .ai file that consists of some designs I need to print in large sizes. Im meant to take said designs, each of them is 70 x 35 cm and print them in the size of 200 cm x 80 cm. Can I get away with making my new files half of their printing size (100 x 40 cm) ? or would that destroy the photo quality when I print them? And what else could I do to reduce the size of said archive? at this point it weights almost 2 gigas and it almost always freezes my computer.

[Barbara Ash]

If your .ai file is all vector objects, the file should be a reasonably small size, and scale up and down beautifully.

However, you mentioned a 'photo'. If the design contains photos, which would be bitmap not vector, you are better off reducing the file size of the photo in Photoshop before placing it in Illustrator. It is always good to communicate with your print vendor to find out their requirements. 

Is the photo a .psd or a .jpg file?

[Criizmeow]

thank you for your answer! the original .ai file was sent to me with embled .jpg images, and I imagine thats the reason why its so heavy, howhever, the size I need to print this designs on is already bigger than the actual size of said pictures to begin with, from 70x35 cm to 200x80 cm. I will try resizing them in photoshop, but I don´t know how much the quality of the print will suffer if I downgrade the size too much.

[Barbara Ash]

Under these circumstances the quality will suffer, as you suspected. The files have been compressed when they were saved as JPG and therefore have already lost some quality. 

TopazLabs has a product called Gigapixel that might be helpful to you. I can't vouch for it because I haven't tried it myself but they have some good products. You could download the trial version and see if it works for you.

[Jacob Bugge]

Criismeow,

Nothing is won by downscaling:

The vector parts give the same file size contribution regardless of scale.

The raster parts (photo(s)) must have the right resolution at the final size (ask the printer), which can only be obtained with a corresponding size in pixels x pixels, and that is what determines the file size contribution. So you need the exact same image (quality) even if you scale down; scaling down only increases the resolution at the downscaled size.

[Criizmeow]

thank you so much for this clear explanation, you saved me many hours of confused frustration trying to make the file smaller.

[Luke Jennings3 · Accepted solution]

Producing a PDF at 1/2 size is common practice. If you have multiple designs in one .ai file, it might be a good idea to split them into individual files, that should keep the size manageable. You can determine the effective resolution (ppi) of your images by turning down the little arrow at the bottom of the links panel. The effective resolution changes as the image is enlarged or reduced in Illustrator. If you are creating your file at 1/2 size, your final effective resolution would be half of the ppi indicated in the links panel. Generally, large format printing does not require the same high resolution as small format work, as it's normally viewed from a greater distance. You can also check the effective image resolution in Acrobat using the Output Preview Tool (Preview: Object Inspector). Here is a link to some rule-of-thumb resolution numbers:

http://resources.printhandbook.com/pages/viewing-distance-dpi.php

[Criizmeow]

thank you, I ended up separating the designs in individual files to make them more maneagable, I will also be using the chart in my future projects, very useful!

[Jacob Bugge]

Criismeow,

If you decide on downscaling to 1/2 size, and if you use any raster effects, you will also have to ensure that they have the right resolution at the final size, which requires your doubling the resolution in the Effect>Document Raster Effects Settings.