I would like to discus printing and how the resolution of the image affects the maximum size that an image can be printed.
Typically today most consumer cameras are somewhere between 12 and 20 mega pixels. This sounds like a lot right? A lot of professionals would argue that current mega pixels are already too high. The race of camera manufactures to ever increase their mega pixel counts is often criticized. In many cases this would be a valid argument. However there are valid reasons why you need lots of mega pixels.
Let’s look at an case study.
A lot of people who run fine art photography businesses offer their images up to around the 1.5 meter wide mark. So what does it take to produce a quality image of that size? For the purpose of this article I am only considering fine art prints on high quality paper mediums such as Fuji Crystal Archive. I’m not considering mediums such as Canvas where you can get away with printing large with lower resolutions files due to the media texture.
First consider dots per inch (dpi) for our purposes are equivalent to pixels per inch (ppi). It is widely accepted that 300dpi prints will give a very good quality print. Some may argue 240dpi while some printers will print to 400dpi. This allows us to make the following calculation
Pixels needed on the Long edge of the image file = Long side print size (inches) X DPI
So for our 1.5 meter print you would need.
Pixels = 60 inches X 300 = 18000
We can take this further to work out the total megapixels of the file necessary. Let’s assume a 3:1 panoramic image with a Long edge 60 inches (as above) and a short edge 20 inches. For the short edge we need.
Pixels = 20 inches x 300 = 6000
If we multiple the pixels required on the long and short edge together and divide by 1 million we get the total mega pixels required.
6000 X 18000 / 1000000 = 108 Mega pixels
That’s a lot and is what will be required to get great image quality if you inspect the photo at 1 feet or less. That gives us our next consideration – viewing distance. If you don’t care about someone inspecting your print at one foot or less then you can apply the following general rule.
Pixels required for a particular viewing distance = pixels / viewing distance in feet
This can be applied to either the Mega Pixel requirements, the long or short edge pixel requirements. So in the above example if we only intent to view at 2 feet or more we require 54 Mega pixels
Let’s put that into perspective.
The Nikon D800 sensor size is 7360 pixels long side X 4912 pixels short side for a total of approx. 36 mega pixels. As of 2013 this is the largest mega pixel digital 35mm camera available and it still does not deliver enough resolution for the requirements of the case discussed above i.e. a 1.5m wide fine are print on quality paper.
This is the primary reason why multi image stitching is used by many photographers that use 35mm digital cameras who wish to print large. It is worth mentioning that there are multiple software and techniques to increase capture resolution in post production. In my opinion there is no substitute to having the required resolution at the point of image capture.
The particular technique I use to capture my panoramic typically uses between 6 and 10 frames for a single row panorama. This will usually end up with an image greater than 150 mega pixels.
In addition to multiple image stitching there are other options to achieve high resolution such as medium format both film & digital cameras. There are pros and cons to each method but that discussion is for another day.
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