Pixel Density & How Does It Matter

As full frame digital cameras become the norm, the digital camera landscape is changing. More and more photographers intend to move to full-frame or plan to in the near future. One aspect of the full-frame sensors in the loss of pixel density. Let’s see what pixel density is, how does it matter and it’s effects and ramifications on photography.

What Is Pixel Density

Pixel density is simply the number of pixels crammed per fixed area of a camera sensor and is measured in pixels per inch. Higher the number of pixels in the same area, more the density.

How To Calculate Pixel Density

I am not going to give a mathematical explanation of calculating pixel density because I know it would make most people yawn :-o. Instead, I shall provide a very simple illustration for you to understand . Consider two camera models – the Sony F828 and Canon 20 D DSLR. Both these cameras have a similar resolution, i.e. 8 MP. But Sony F828 has a comparatively smaller sensor. Thus, using the simple formula, Pixel Density = Number of pixels/Imaging area (of the sensor), we know that the imaging chip of the Sony F828 will be tightly packed with more pixels per unit area, resulting in a high pixel density.

Breaking The Myth Of Pixel Density

Pixel density is not measured in terms of pixels-per-fixed-area of the monitor. Pixel density is measured  in wrt. the sensor’s area and not the monitor area. For example, the Sony F828  (mentioned above) has a sensor as small as 1/16^th of the full frame size and the pixel density is very high. One thing worth mentioning here is that a sensor of high pixel density needs a sharper lens because of their better sampling. Thus a 35 mm film /sensor might go with the standard 35 mm lens but for a sensor with a higher pixel density, a lens with higher focal length will be required.

The Fine Print About Pixel Density

A very important factor that the manufacturers do not tell you is that two cameras with same resolution but with different sensor sizes will have different pixel density. And since pixel density directly impacts the image output, you may end up paying more money for a camera with a more mega-pixel sensor but smaller physical sensor size and hence loss of information in your images. Smaller sensors with more pixel density might give you sharper pictures but they also crop the field of view. Also check out my other article on Bayer Interpolation. A smaller sensor means greater lens magnification (or less wide angle reach – thus requiring very small focal lengths for wide angle coverage).

Crop Factor Of A Camera

To understand how the smaller physical sensor size affects their photograph the manufacturers provide the camera’s crop factor (also known as focal length conversion factor) in the camera specs. A crop factor simply means that the manufacturer has used a smaller sensor (with a lens adjusted for the size) for his camera as compared to a full-frame camera.

Impact Of Pixel Density On Your Pictures

A small sensor is not always bad. Sometimes, a camera with a small sensor and higher pixel density technically might be useful for shooting smaller objects like birds and insects since the larger crop factor in such a camera gives a greater magnification, narrower field of view and sharper image. (That doesn’t mean you must carry multiple cameras everywhere, your cellphone’s camera will do). To the contrary for professional photographers (and especially the) landscape photographers a camera with a large sensor is a must because of the wider field of view since such sensors capture a greater amount of light, produce less noisy picture and a higher dynamic range and are desirable for all professional photographers because of the larger pixels.

Pixel Density And Dots Per Inch — The Difference

People often refer to pixel density as dots per inch but these two terms are quite different from each other. While pixel density refers to the number of pixels per unit area of the sensor, dots per inch refer to the the number of ink dots per square inch of the printed page (image). Higher the number of dots, more efficient is the printer, better the quality of the printed picture. Therefore, printers are rated as per their efficiency in dots per inch or DPI.

A good resolution camera with a large sensor will always give you better quality pictures. But a larger resolution is quite desirable to keep the pixel density high. A total value for your hard earned money, isn’t it?