What’s the perfect image resolution

What is the best resolution of images for large format printing? While there is no one simple answer to this question, there are 4 main steps you should know. For those who what the short answer, see the general guide below, if you want to understand why and how to apply that knowledge to a practical example then read on…

General Resolution Guide for Different Material Types

Recommended minimum–maximum image dpi @ actual size:
Self Adhesive Vinyl: 100–150dpi
Quality Papers & Films: 150–200dpi
Flex Banner: 50–100dpi
Banner Mesh: 30–72dpi
Rigid Panels:* 72–150dpi
*Corflute/Composite Panel/Foam Board

Example: SHORT ANSWER
Take for example of a 3m x 1.6m Self Adhesive Advertising Banner which includes a background image. You’ll need to create your artwork at 25% of actual size with the image set at between (400dpi minimum = 100dpi actual size – 600dpi preferable = 150dpi actual size) at 750 x 400mm to target a (medium-high quality) print on a premium large format printer like a Roland XC540. To get the complete story why and how, read the 4 steps below.

Example: LONG ANSWER
To calculate the best resolution for you image you need to work in reverse from the end use back to the available image. Here are the 4 steps:
1. What are you printing and at what distance is it viewed from?
2. Know what printer and material you plan to print on (know the printers ’sweet spot’)
3. Create your artwork at the appropriate scale and size for output
4. Generate your image to match the scale and size of your artwork
1. What are you printing and at what distance is it viewed from?
For the purposes of this article let’s take an example of a 3m x 1.6m Self Adhesive Advertising Banner which includes a background image overlaid with text and a logo (as a side note always make sure your text and logos are ‘vector’ based). The banner needs to be viewed instore from a medium distance so the image should needs to be crisp, as a result we’ll need to print at a high quality setting through our printer.
2. Know what printer and material you plan to print on
Most large format printer have optimal print resolutions at certain speeds of operations. For best quality of print you need to sacrifice speed of printing, but generally you’ll find a happy medium with your printer that produces very good print results on most media at an acceptable print speed, think of this as your printer ‘sweet spot’. In your RIP software there are plenty of auto options based on the material you plan to print, but you don’t have to a use the greatest resolution setting. Do some comparison tests with your printer using the same image so you can benchmark which setting gives you best results in a timely fashion. In this example our printer is a Roland XC540 which can print to a maximum of 1440 x 1440dpi but its ’sweet spot’ is 720 x 720dpi for quality general vinyl use. An image suitable of printing at this setting would be between 100 – 150dpi at actual size in photoshop. In most cases a resolution of around 100dpi will be adequate, but if your image has a lot of fine detail then you should use 150dpi, but remember this will make your file considerably larger.
3. Create your artwork to the appropriate scale and size for output
Most artwork for large format prints is done at scale, so your image will need to be sized appropriately to that scale. For instance, if your artwork is 3.m x 1.6m then using a  25% scaled size equals 750x 400mm. So at 4x scale a 100pdi will need to be 400dpi or a 150pdi will need to be 600dpi.

4. Generate your image to match the scale and size of your artwork
Open the image in photoshop and select millimetres as the measure, then clicked OFF ‘Resample’. Type in the target resolution (let use 400dpi in this case) to see if your image will match or be greater than the size required of 750x 400mm. If it is greater then you can downsize it appropriately or crop it as desired. If the image is significantly smaller then it may not suitable for use.
Extra tip 1 – If you have no choice but to use this undersized image, then try this. Use (288pdi) as your target resolution, which equals 72pdi at actual print size in this case. If it is still a lot smaller than your required 750x 400mm size then it is not suitable for use. If it is now close to the size required you can force the file size up by increasing the image dimensions. Make sure you do this with with ‘Resample’ clicked ON and ‘Preserve Details’ (Enlargement) selected in below drop-down. You’ll also notice a ‘reduce noise’ slider appear, start moving the slider to level 3 to test the smoothing effect to remove the added noise, then slide it in increments of 3 to test the results and see what looks best. Once you are happy with the result click OK and save your file ready for placement in your artwork.
Extra tip 2 – If your image is too small or noisy you could consider enlarging it to the size required using the method in tip 1 above, and then run an effect filter through the image which helps to break down the noise and any visible pixels. Go to ’Stylize’ under Filters and try the: Diffuse, Oil Paint or Wind filters. If none of these are suitable there is plenty of other filters available for photoshop you can download.

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