Today’s Question: Please, help me clarify a big doubt. I have a Canon 5D Mk III (22.6 Megapixels, 5760 x 3840). With an image that “big” (22 megapixels), if I were to print it using a printer with a maximum printing resolution of 2880 x 1440 dpi, how big can I print an image without any interpolation? The printer is an Epson and the maximum printing area is 17×22″.
Tim’s Quick Answer: The dot per inch (dpi) resolution indicated for the printer (for example, 2880 dpi) relates to print quality, not to the maximum potential output size. To determine the output size without resizing the native capture, you need to calculate based on the resolution used to render the image. In general you can assume a resolution of somewhere between 300 and 400 pixels per inch. Thus, your 22 megapixel captures can be printed at 11×16 inches without resizing (and even bigger with some resizing).
More Detail: The actual resolution used by the printer software to render image data for printing varies from one printer to the next. In general this resolution falls somewhere in the range of about 300 pixels per inch (ppi) to about 400 ppi. Many Epson printers, for example, use a resolution of 360 ppi, although some newer models actually use 720 ppi.
The reason the “advertised” resolution for the printer is higher then the “actual” image resolution is that the printer specifications refer to droplets of ink rather than pixels in the image being printed. As you can imagine, it requires multiple droplets of ink to produce the specific color for each pixel in a photo.
So, in this case let’s assume an image resolution for printing of 360 ppi. You can then divide the pixel dimensions by the resolution value to determine the native output size. So, 5760 pixels divided by 360 ppi is 16 inches, and 3840 pixels divided by 360 ppi is about 10.7 inches. Thus, a native maximum output size of about 11×16 inches.
However, it is very important to keep in mind that you can enlarge an image and still retain excellent print quality. As a general rule of thumb I would say you can feel very comfortable doubling the dimensions of a photo, as long as the original capture is of very good quality. That would enable you to produce a print of about 22×32 inches in this case, for example. And in reality, the larger the print size the greater the typical viewing distance, so you can often “get away with” an even larger print size.
To be sure, it can be very helpful to understand the “native” print size potential for the images you’re capturing. Just don’t forget that you can still achieve excellent results when enlarging a high-quality photo to produce a larger print.