MEGAPIXELS, PRINT SIZE, AND THE 300 DPI RULE

The 300 DPI rule is an interesting one; it comes from the printing industry and is generally considered as a rule of thumb for printing images. DPI stands for “dots per inch”. Let’s say, you have an image you want to print at 8 x 10”; the printing store assumes the image will be seen from a distance of at least an arm’s length. At that distance, a resolution of 300 DPI is good enough to not make the individual pixels stand out; this makes the image seamless. Distance here is a factor too. For example, the more the distance, the smaller the DPI will be required for a ‘good enough’ print. For instance, if printing a billboard, a 50 DPI resolution would be acce

Dots and pixels are often considered as synonymous. However, they are technically not the same thing. Often times, you would hear the term, “resolution”, in the same mix; it is one of the most talked about aspects and sought after parameters in a digital camera. Resolution stands for how many pixels are crammed onto a sensor (the heart of the digital camera). More details can be captured at a higher resolution; thereby, larger prints can be made.
So, what are these pixels? They are the tiny photo-diodes that make up the surface of the sensor; they capture light and convert them into electronic signals. “Megapixel” is another term that is closely associated with a camera’s resolution and invariably follows the other. One megapixel is equal to one million pixels.

How do you calculate the resolution you need for a good print? Going by the 300 DPI rule, each dimension of an image needs to be multiplied by 300. Since an image is two dimensional, you need to multiply the two sides to arrive at the total resolution. Thus, if you plan to make an 8 x 10” print, you can calculate the required resolution by using this formula: Length x 300 (pixels) x height x 300 (pixels) / 1,000,000; in this case, it is 7.2 megapixels.

When all we need is a sensor of 7.2 megapixels to produce a sharp 8 x 10” print, why are we told we need a higher resolution? Part of it has to do with the marketing techniques of these camera companies; they have to sell better, sharper, higher resolution cameras and outdate older models to make a profit. However, part of it is legitimate; higher resolution does have its applications, especially in commercial shooting, such as stock photography.
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Lens sharpness is a major factor that affects picture quality. Even though you may have a 16 megapixel camera, when paired with a kit lens, you still get less than the actual resolution the camera is capable of. For example, a D5300 (24.2 megapixel APS-C camera), paired with an 18-55mm VR kit lens, will produce only 9 Perceived Megapixels (PMP). This means your images can only be printed at around 8 x 10”, or slightly larger, to produce a sharp print, not the 20 x 13” that the specifications claim. Next time, think twice about buying that camera just because its megapixel count is high.