what is the megapixel in a camera? is it the resolution? how to calculate it? is it by multiplying resolution?

Answer 1

"Megapixel" (as commonly stated for cameras) is the total number of pixels, in millions, that the camera is capable of producing in a photograph.

"Resolution" (in its purest sense) is also the number of pixels in a photo. It tells you how many pixels you have to work with. Usually it is stated as Width times Height (in pixels).

However, there is a lot of confusion about "resolution" because it expressed in several ways for different purposes.

Some cameras let you choose different picture shapes (e.g. 4x6 shape vs 4.5x6) by selecting a different "resolution". Then they also let you choose different "quality" by choosing lower or higher "resolution". But in both cases, they still really mean how many pixels (Width times Height) you will get.

"Resolution" is also used to mean the "density" of pixels in a photo (how many Pixels per Inch (ppi)) are in a photo. This is often used when thinking about printing and is confused with the number of Dots per Inch (dpi) the printer can do. ppi and dpi are not the same at all.

ppi is just arithmetic. If you have a photo that is 1000 pixels wide and say it is 4 inches wide, you have 250 ppi. If you say that it is 16 inches wide, you have 62.5 ppi. Same pixels (resolution), just spread out differently.

This only matters when printing. The 250 ppi picture, printed at 4 inches, will look good; the 62.5 ppi picture, printed at 16 inches will not.

This is why higher megapixel cameras allow you to print bigger photos - more pixels!

Answer 2

Megapixel

A megapixel is 1 million pixels, and is used not only for the number of pixels in an image, but also often to express the number of 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, either Charge-coupled device (CCD) or CMOS image sensors, consisting of a large number of single sensor elements, each of which records a measured intensity level. In most digital cameras, the sensor array is covered with a patterned color filter mosaic having red, green, and blue regions in the Bayer filter arrangement, so that each sensor element can record the intensity of a single primary color of light. The camera interpolates the color information of neighboring sensor elements, through a process called demosaicing, to create the final image. 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. Thus, a so-called N-megapixel camera that produces an N-megapixel image provides only one-third of the information that an image of the same size could get from a scanner. Thus, certain color contrasts may look fuzzier than others, depending on the allocation of the primary colors (green has twice as many elements as red or blue in the Bayer arrangement).