Image Quality Recommendations
Print Resolution is simply the level of detail in a printed image. Higher resolution means higher detail and can be measured in dots per inch (DPI). The more dots (of ink) that are printed per inch, the higher the resolution of the image – therefore the higher the quality in terms of sharpness and detail. When it comes to printing, resolution is super important, as a high-quality image looks beautiful and professional, whereas a low-resolution image looks fuzzy, indistinct, and possibly even pixalated if low enough and completely unprofessional. When you are creating your source image (the image you want to be printed), make sure it has a suitable resolution – minimum of 300dpi.
You can always scale down in size, but never scale up; at least not without losing quality. Make sure your image has the highest resolution and image dimensions you can get. The only consideration is that you will need different resolutions depending on how large the printed image will be, where it will be displayed, and how it will be printed. For example, an enormous billboard can be printed with a lower DPI than a small leaflet, even though it is larger in size simply because you view it from a distance so you will not see the low resolution. One of the most common problems faced by printing companies, is clients uploading digital files with a resolution that is too low to print. When it comes to source images, higher resolution (DPI) is always better.
Resolution does not mean size.
Resolution is a measure of pixel density, not size. A poster measuring 2 x 3 meters could have the same DPI as a business card measuring 50 x 90 millimetres. Remember it is dots per inch, so it does not relate to the size of the image, or of the dots. As already discussed, a large image (such as a billboard) can have a low DPI if it is going to be displayed very far away (as is usually the case with larger images), as the human eye resolves the image, hence resolution. Close up it will look very pixelated and low quality.