Learn Photography with Jain – Megapixel

CCD from a 2.1 megapixel Argus digital camera.
A megapixel (MP or Mpx) is one million pixels, and is a term used not only for the number of pixels in an image, but to express the number of image sensor elements of digital cameras or the number of display elements of digital displays. For example, a camera with an array of 2048 × 1536 sensor elements is commonly said to have "3.1 megapixels" (2048 × 1536 = 3,145,728).

Digital cameras use photosensitive electronics, consisting of a large number of single sensor elements, each of which records a measured intensity level. These sensor elements are often called "pixels", even though they only record 1 channel (only red, or green, or blue) of the final color image. 

Citing megapixels (MP) is a popular shorthand way to express the resolution of a digital camera in terms of how many millions of individual pixels (picture elements) are present in the image at time of capture.

Note the significance of the phrase ”...at time of capture” in the definition above. Resolution can be occultly increased through interpolation, a process that analyzes actual data and makes intelligent guesses to increase the quantity of information. The number of physical pixels doesn’t change. The camera’s signal processing engine fills in the blanks based on complex mathematical algorithms.
After an image is captured you can change the number of pixels that it contains, sometimes without even realizing it. When we Resample an image we change its pixel dimensions. Upsampling involves adding pixels, while Downsampling requires discarding pixels. Both procedures degrade image quality, sometime significantly. People often do this indiscriminately when resizing images to print them. Below is an extreme example of an image that’s been degraded by Upsampling.
Resolution has a horizontal component and a vertical component. An image that is 1200 pixels tall by 1800 pixels wide contains 1200×1800 or 2,160,000 pixels. That’s about 2-megapixel. One megapixel is not actually one million, although it’s close. 1MP = 1024×1024 = 1,048,576, so we accept with nearly 5% inaccuracy because, well, it really doesn’t matter just as long as everyone counts them and labels them the same way.
Incidentally, an image that measures 1200×1800 is said to have an Aspect Ratio of 2:3, which is the same as a 4×6 inch print.
Many camera specifications show one number for Total Pixels and a lower number for Effective Pixels. The first, larger number indicates how many pixels can be counted on the entire surface area of the CCDor CMOS imager, including the edges that are not used. The second number is the only one that’s meaningful, as it indicates how many are actually recording data.

How many megapixels do you really need? It all depends on what you want to do with the image. Unfortunately, digital cameras are lumped into categories based on the number of megapixels they can capture, and uninformed consumers make erroneous conclusions about image quality based on that single label. Having more pixels does not always mean better images. These images were shot with a humble 3-megapixel camera.
How many megapixels do you need?

Having more megapixels can offer some distinct advantages, however. Higher resolution images produce larger prints without loss of quality. If you make 13×19 inch prints, for example, you need all the resolution you can get. The second advantage, one that’s all too often overlooked, is that you can crop smaller portions of a high-res image and still retain high quality.
On the other hand, if you are producing images for a website, or mostly print 8×10 or smaller, a nice 6-to-10 megapixel camera will serve you fine. Like many photographers, however, you may cling to the notion that someday you’ll want to turn your images into gigantic poster-sized prints. In that case, shoot large RAW images now and you won’t regret it later—that is, unless you run out of hard drive space. Read on.
High resolution comes at a high price. More megapixels mean larger files. Large files make for longer download times and can really fill up a memory card fast. Ditto your hard drive and backup externals. It’s not unmanageable, but you should be prepared. 

Source: Jon Sienkiewicz@photo.net, Wikipedia
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About author

Jain T. Chacko is a freelance writer by passion and an Engineer by profession. Active in the blogger world under the title "WhatJainSays" ever since 2010. Through "whatjainsays.blogspot.com" he shares the latest buzz in the e-world, spread across thousands of websites. Loves sharing and learning also prays for world peace.
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