Large format print is a specialist area within the print industry which can cause inexperienced designers more than just a few headaches.
The term ‘large format print’ (also called ‘outdoor’ in the advertising media world), is used to refer to types of
printed material that is output at very large sizes. Think billboards, tradeshow displays, bus-back advertising and printed mural or building signage. A lot of this material is digital printed on substrates such as synthetic paper, adhesive paper, canvas, fabric and aluminium composite board (ACM).
When it comes to designing for large format print—creativity aside— understanding some of the common technical issues and differences versus offset printing will ensure a better end result. GSM sat down with John Gallacher from Adgraphix to find out more. Here are some of the key things to keep in mind:
Image resolution and file size:
Image resolution and file size are both constant challenges when working in large format print mediums. Images for offset printing are typically set up at 300ppi at 100% of their physical output size. This is to ensure good reproduction.
However, images for large format print can be much lower in resolution. Due to the audience viewing the printed design from further away than they would with offset printing, working at 300ppi is unnecessary. Optically, the viewer won’t notice the difference in image quality when standing at the intended distance.
This concept is doubly important, because if you try to work with a 300ppi Photoshop file for something like a 6 metre billboard, your image file size will often balloon so large that it becomes unworkable.
The chart below shows effective minimum image target resolution based on the anticipated viewer distance. Basically, the further away the audience will be, the lower the required resolution.
As an example, if a 6 x 3 metre billboard is set five metres back from the roadside the required image target resolution for
your image only needs to be 30ppi. At this distance, the viewer will not recognise the difference in quality between a 30ppi image and a 300ppi image.
Another key point about resolution is the opposite of this—i.e., working with images that are too small. There is nothing worse
than going through the design process, showing your client an A3 printout of your design, getting sign off and then realising
that the image you have used is not available at a high-enough resolution for the final artwork size (this happens a lot). Avoid this situation by working towards the correct image target resolution at the start. If an image is not large enough to meet the
minimum target resolution, then don’t use it. Don’t expect this can be ‘fixed’ at the artwork stage.
Check with your large format print supplier at the start of the project how they would like the artwork supplied. Native files are often preferred (i.e., .psd file for Photoshop, .ai for Illustrator etc). Supply any linked images also in a native file format. Some printers may prefer PDF files—but it’s best to ask first.
Where you can, it’s best to work at actual size (scale 1:1). However, for a lot of large format artwork such as billboards, working
at a scale of 1:1 is not possible due to software limitations. For example, Illustrator/InDesign may not allow artboards large enough. In this situation, you can work at a reduced scale, such as 1:10 (10% actual size). Your printer will then enlarge the artwork to the actual size during the printing process. Don’t forget to tell them what scale you are working to!
However, when you scale down artwork, you need to be aware that the resolution of any images you are using need to be higher to compensate for this enlargement if they are going to match your target resolution.
If your target resolution at actual size is 30ppi, and you are working to a scale of 1:10, your scaled down images will need
to be 300ppi to compensate.
The safest work methodology for supplying large format artwork is always to convert all fonts to outlines/paths. Don’t assume your printer will have the fonts.
Bleed & trim:
Check with your large format print supplier what bleed they require on your artwork. Keep in mind that many types of large format printed material require significantly more bleed than is needed for offset printing. This is due to wraparounds that may be required for installation.
Like all print work, use CMYK mode— not RGB—in all artwork files and links.
Working with black:
In your artwork, ensure all BLACK is specified to be the same CMYK mix throughout. Do not use blacks with different colour breakdowns, as the difference may be visibly noticeable at actual size.
Raster Effects and transparency in Illustrator or InDesign:
Think twice about using raster effects (drop shadows, inner/ outer glows etc.) or transparency in either Illustrator or InDesign.
These effects mimic similar effects available in Photoshop—whilst they often look fine on-screen in Illustrator or InDesign, they can cause all sorts of issues at the printing stage. It is much safer to recreate these types of effects in a linked Photoshop file.
If you are using colour profiling, ensure the profiles are synced across all applications.
Three Most Common Mistakes with Large Format Artwork Files:
- Interpolated raster images:
If you have a design that uses an image that is too small at actual size, don’t ‘blow it up’ in Photoshop (this is called interpolation). The end result will be a soft, fuzzy image. The best solution is to find a high-enough resolution image from the start—and not try to fix things at the end.
- No images supplied:
Sometimes we receive the native artwork file (such as an .ai file), but without any of the linked images use d in the design.
We can’t print your artwork if there are missing images…!
- Fonts not converted to paths:
If we need to open an artwork file for some reason (and we often do), if the fonts have been left live, it can create a real headache—there is a good chance we won’t have the correct matching font. It’s always easier and safer to convert your fonts to paths before sending your artwork to print.