What resolution should a large format artwork for print be?
For wall-sized graphics and large banners (e.g 3m x 5m), what is an acceptable PPI for print?
As I understand it 300 PPI is the typical for 'small' artworks (esp. for clean text resolution). However, for small artworks, the audience usually engages at a much closer distance. Therefore in the interests of keeping a bitmap file down to a reasonable size can you get away with a much-reduced PPI for a large format/banner print?
In general you should use vector graphics in the artwork wherever practical, and deliver final artwork to the printer in PDF or other vector format. Your finished print will then be limited only by the output resolution of the print device.
This is particularly important with text and line art â€” visible rasterization in the finished print will be very obvious and look amateurish.
While a PDF can contain photographic images, they will have a fixed resolution, and while 300 ppi is a good rule of thumb for publications and small posters viewed at close range, there's no way you'll achieve anything close to that at the dimensions you're talking about. Certainly you should aim for as high as possible, but I don't think there's a hard-and-fast lower limit. I've certainly ended up with around 75ppi in photographic elements of 2m high event banners, which looked fine at relative distance. I never felt the need to do any interpolated upscaling of the raster images.
So, again in general, your workflow would be:
- produce raster elements in Photoshop and output as TIFF files
- create complex vector elements like logos or illustration in Illustrator and output as EPS or PDF files
- compose the final artwork in InDesign, linking in the raster and vector files, adding text and simple vector elements like colour blocks.
- output the composite PDF from InDesign, ensuring that raster elements are output at their native resolution, i.e. not downsampled to a particular output resolution.
I like the accepted answer, it has good advice, but I thought I'd expand on it a bit.
For wall sized graphics and large banners (e.g 3m x 5m), what is an acceptable PPI/DPI for print.
Here's definitions, so we know what we're talking about.
- DPI = Dots per inch = units used to measure the resolution of a printer
- LPI = Lines per inch = The offset printing 'lines' or dots per inch in a halftone or line screen.
- PPI = Pixels per inch = the number of pixels per inch in screen/scanner file terms.
Now you said "As i understand it 300 DPI is the typical for 'small' artworks (esp. for clean text resolution)" -- here you're confusing DPI with PPI (often done.) Raster artwork for print is generally scanned at 300 PPI. Why? Because most raster artwork is printed with CYMK processes at a maximum (generally) of 150 LPI. The rule of thumb is that we need 1.5 to 2 times the LPI in PPI to get acceptable results.
Why are most things printed at 133 or 150 LPI? Because at reading distance for CMYK printing the dots aren't generally discernible. Because of high-speed printing and cheaper paper/printing of newspapers, they are often as low as 85 LPI, so you can see the individual dots easily on the funny pages.
So your question can be distilled down to: what is the minimum LPI halftone screen I need so that it's not distracting at the distance the poster will be viewed? I did a little searching, and actually found a research paper on this subject. The subject was black and white printing, but since colour halftone dot patterns should even be less noticeable, I think the advice can be extrapolated.
Here's the chart:
Distance Present Study 20 feet / 6 meters greater than 10 LPI 18 feet / 5.5 m 18.75 LPI or greater 16 feet / 4.9 m 18.75 LPI or greater 14 feet / 4.3 m 37.5 LPI or greater 12 feet / 3.7 m 37.5 LPI or greater 10 feet / 3 meters 50 LPI or greater 8 feet / 2.4 m 65 LPI or greater 6 feet / 1.8 m 85 LPI or greater 4 feet / 1.2 m 100 LPI or greater 2 feet / 0.6 m 133 LPI or greater 1 foot / 0.3 m 150 LPI or greater 6 inches / 15 cm 150 LPI or greater
Presumably, for a banner 3m x 5m, you'd be standing at a minimum of, say, 10 feet. (Just eyeballing the wall here.) So, by this table, you'll need 50 LPI minimum. That would mean your raster graphics should be about 100 PPI, or 75 PPI at 12-14 feet. Considering that and the fact that 2x LPI is pretty conservative for reproducing fidelity (often 1.5xLPI is "enough"), this agrees with @e100's advice of 75 PPI being acceptable.