If you intend to sell prints using POD services, or if you are creating digital art that will be printed for some reason or another, such as book cover illustrations, then this is something you will likely have to deal with. I get it from time to time, especially when doing illustration contracts. A person from the print shop or publisher will tell me that my image has too low of a DPI and that they can’t print it. This person does not know what they are talking about. Now it could be that that what they mean is that the image’s resolution is too low, but, for my images, which are usually in the 40 Megapixel range, such is not the case. Most of the time they are just ignorant of what DPI really means when it comes to a digital image file.
The subject of DPI comes up quite a bit when you deal with digital art. DPI stands for “Dots Per Inch”. People who deal with printed media seem to think it is an important number. Indeed, when you actually print something, it can be somewhat important. An image printed at 300 dpi looks great to the human eye from just several centimeters away; at 50 dpi through, it would look pretty grainy close up. However, when it comes to digital art in its digital form, that is, as an image file on the computer and not printed out, it is almost completely irrelevant. In fact, it is actually less relevant even when printed than some might have you believe.
DPI has virtually no relevance for a digital file. It is just a number in the metadata (known as the EXIF data) of an image file that suggests to a printer how dense to print that image. That suggestion can easily be (and usually is) overridden when a print is made. For instance, if I have an image file where the EXIF data states 300 for the dpi and the image is 3000×3000 pixels, the bitmap data is exactly the same as a 100dpi version of the same image that is also 3000×3000 pixels. The only difference is that if you print them both without specifying a print size then the 300 dpi one will print a 10″ x 10″ print and the 100 dpi would give you a 30″x 30″ print. Now, if you took the 100 dpi and told the printer to give you a 10″x10″ print it would actually give you a 300dpi print thas is ten inches on each side, i.e. you’d be overriding the default dpi.
In other words, resolution is what matters. An image with a high resolution can print a larger, higher quality image than one that has a low resolution. When it comes to digital art, the number of megapixels is what is important, not dpi. That is one of the reasons I create all of my art at at least twelve megapixels and quite often as much as sixty. That size gives lots of printing options.
Not only is DPI irrelevant to digital files, is also overrated when it comes to printed material. It is true that the higher the dpi, the higher the quality of the print. Print shops often insist that 300 dpi is the gold standard and that all images be printed at that or a higher resolution. 300 dpi does indeed look great from even a few centimeters away, but how often do you really look so close at a piece of wall art that your nose is nearly touching it? Probably not often. Most people look at wall art from a few meters away. At that distance, a 300dpi and a 100dpi print of the same image at the same physical dimensions would look identical. If you don’t believe me, get a close up look at a billboard image one day. From arm’s distance, you’d see nothing but a bunch of colored dots. Billboards are printed at around thirty dpi.
Some people might tell you that DPI is not important for an image but that PPI is. They don’t know what they are talking about either. PPI stands for Pixels-Per-Inch. It applies to monitors not files. For a digital image file, this is meaningless. Where is does come into play is when an image is displayed monitor. A monitor with a high PPI will show images smaller but with higher quality, but, again, for the image itself, the resolution does not change. It’s the monitor that determines the PPI, not the image.
I hope that clears a few things up for some!
Don’t forget to check out this week’s sponsor, Dick Blick Art Materials (since I offer this site for free, I have to fund it somehow 😉 )