: I need to print an image at a certain size. What dimensions and resolution should I use? (This question is meant to be a resource to direct others to given that this is a common question.)

@Lengel450

Determining PPI Resolution given the Viewing Distance from the image

For Raster (halftone screened) graphics, the PPI resolution is determined in two steps using only basic arithmetic. There's nothing mysterious.


Step 1. Determine the necessary LPI (Lines Per Inch)

A simple formula for the minimum acceptable LPI for viewing distance has been determined by the Specialty Graphic Imaging Association
using the "Rule of 240."
240 ÷ the viewing distance = minimum acceptable LPI.
Step 2. Once LPI is chosen, finding the PPI is a snap.

The Relationship between LPI and PPI is as follows:
PPI = LPI x QC x Magnification


In the above formula, LPI is the chosen line screen, “QC” is a quality-control factor, and magnification is the ratio (result) of the reproduction size divided by the original size.


Photoshop uses three QC factors:
“1” for draft, “1.5” for good, and “2” for best.
“2” results in 4 pixels per halftone dot.
Some gurus suggest a QC factor of 1.7 (3 pixels per halftone dot)
derived from the Nyquist frequency limit (a formula).


You MUST always check an image’s resolution in the Image > Image Size dialog box (Photoshop)


Once you know PPI, you can check to see if the actual number of
pixels in an image will support the LPI you’ve selected.
If an image has too many pixels for the application, downsample it
and then SAVE AS under a different file name. Don’t overwrite the
original large file because you may need the additional data for a
higher LPI reproduction.
If an image has too few pixels for the application, upsampling is
likely to provide unsatisfactory results. Consider decreasing LPI
and/or the QC factor.


TIP: Always size an image to the right number of pixels using Photoshop. While reducing or enlarging using InDesign is possible; doing this will increase the amount of time it takes to output the job. (Time is money).

Vote Up Vote Down

@Holmes874

The only definitive answer to this question is: Ask your vendor.

Every vendor, every printer, every t-shirt maker, etc will have their own particular preferences as to how they want to receive files and how they want them set up. Discussing this with your vendor before you begin is crucial to ensure that the process goes smoothly.

The general rules of thumb, however:

Offset printing of brochures, business cards, menus, postcards, etc.: 300ppi

Generally, for printing materials that you'd tend to consume at an arm's length (brochures, flyers, business cads, etc) you are going to want to set up your file at 300ppi. This will provide enough image data to produce an image of decent quality. If necessary, you can usually drop to 240ppi and still be safe.

Exceptions to the rule:


one color line art: If your image is primarily solid line art you may want to increase the resolution to 600ppi+.
newsprint: lower quality paper, such as newsprint, will have much greater ink-bleed (the process of the paper absorbing the ink). As such, it can't hold the same level of detail as higher quality paper. 200dpi is usually the max for newsprint.
high quality printing and/or stochastic printing: for high end publications, such as photography and art books, luxury glossy magazines, etc, you may be able to benefit from much greater detail and would want to provide higher resolution images.
text heavy files. Note that the 300ppi rule-of-thumb is for photographic/illustration type images. Anything that will be printed with multiple colors (such as CMYK). For type, however, 300dpi is rather low to give fine detail to your type. Ideally, your type would not be part of a raster image file, but rather typeset in a resolution-agnostic file format such as Adobe Illustrator or Adobe InDesign. If you must have small type set inside your raster image, however, you will want to increase the ppi to at least 600.


Screen Printing: no higher than 300ppi

Screen printing quality is heavily dependent on the substrate that it is being printed on, the mesh count (screen frequency), and the ink used. Fine art prints on baryta coated paper can get away with resolutions close to 300ppi. That Hanes t-shirt can likely handle no more than 75ppi.

Inkjet/Giclee: Minimum of 300ppi

Inkjets have gotten amazingly good and a lot of art is now printed directly to Inkjet. The fancy term for this is "Giclee". Today's printers can handle at least 300ppi and many can go much higher--especially those that use 6 color printing.

Large format printing (any method): typically <72ppi - 150ppi

This category can range wildly from advertising posters, vehicle wraps, 2 story billboards, etc. The variable to consider is the distance the viewer will be from the material. A person driving on a highway will never be able to discern the difference between 300dpi on a billboard and 40dpi. You would up close, of course, but the only people viewing a billboard up close are those installing it. Most advertising posters can get away with 100ppi. Vehicle wraps, much less.

Exceptions to the rule:


the vendor may ask you to provide art at a smaller size than the actual printed size. For instance, if a billboard is to be 20' wide, the vendor may ask you to send a file 20 inches wide. If the billboard will be printed at 40ppi, then your 20" wide file would need to be set to 480ppi to allow for the scaling (12X40).


Generic Exceptions to the above rules


All the above rules-of-thumb apply to raster files only (pixel based files such as Photoshop). Vector based files (such as SVG or Illustrator) don't have a resolution restriction. This is the great thing about vector files. These can be scaled to any size and still be output with the correct resolution needed. Whenever you can, work in vector.
non-printing output. This can include things like vinyl cutters, CNC machining, die cut patterns, embroidery, etc. These types of outputs will require vector based files.


Pixel dimensions vs. print resolution

One area that can add confusion is that the ppi setting you see in the PhotoShop file is typically only applicable to PhotoShop--and perhaps other Adobe software. For the most part, most software only cares that you have enough pixels in the image to print it at the size you want to print it at. So, for example, the following two image files are exactly the same image:

Image 1: 72ppi, 720px wide

Image 2: 300ppi, 720px wide

On the computer, those two images are identical because they contain the same amount of pixels. If they were both imported into a program like InDesign or MS Word and sized to look the same size on the page and printed, they'd be exactly the same.

On the other hand, if you were to print directly from PhotoShop (which it should be noted, is rare for printers) you will get two different results. The first will end up being printed 10" wide, and look fuzzy as it's only 72ppi. The second one will be printed at roughly 2.3" wide, and look great, albeit small, as it is set to 300ppi. Same amount of information in each file, but one had much larger pixels when printed.

This is mentioned because some print vendors may work with low PPI settings but large pixel dimensions. Some software may also completely ignore the PPI meta data and only care about the pixel dimensions.

Images for the web

As a footnote, images that are to be displayed on the web disregard ppi settings completely. All that matters is the pixel dimensions. If your image is 600 pixels wide, it will show as 600 pixels wide regardless of the screen and the size of pixels on said screen. 72ppi is the 'default' setting for web images, but it's just tradition, rather than any sort of technical requirement.

(Everyone: Please edit/add to this as you see fit!)

Vote Up Vote Down