Image Sensor Resolution
When you take a photo with a digital camera, each of the pixels is captured by a single photosite on the image sensor. A computer or printer uses the pixels to display or print photographs.
To create the image, the computer divides the screen or printed area into a grid of pixels. Then it uses the values stored in the digital photograph to specify the brightness and color of each pixel in the grid. This process is called bit-mapping, and the resulting digital images are called bitmaps.
Once a digital image is printed or displayed on a screen, its quality is determined in part by the number of pixels used in creating the image (its resolution). The number of photosites on the image sensor determines the maximum number you are able to capture.
The aspect ratio is the ratio of image width to image height, and it varies among image sensors. The ratio of a square is 1:1 (the width equals the height), and the ratio of 35 mm film is 1.5:1 (it is 1.5 times wider than it is high).
The aspect ratio determines the shape and proportions of your digital images. When an image has an aspect ratio that differs from the device on which it is being displayed or printed, the image must be cropped or resized to fit. It's a bit like trying to fit a square image on a rectangular piece of paper. The aspect ratio of a camera can be calculated by dividing the larger number in its resolution by the smaller number. For instance, if a sensor has a resolution of 1536×1024, you would divide 1536 by 1024, for an aspect ratio of 1.5.
Aspect ratio is something you encounter every day but may not be aware of. For example, the switch from a regular TV screen to a wider high-definition screen is a change in aspect ratio. Because movie screens are wider than TV screens, they also have a different aspect ratio than your TV.
Although resolution is an important determinant of the quality of an image, another equally important factor is color depth. Color depth is the term used to refer to the number of colors in an image. It is also called pixel depth or bit depth. Older computers have displays that only show 16 or 256 colors. Today's computer systems display what is known as 24-bit true color. The term true color is used because the systems display 16 million colors, which is about the same number as can be discerned by the human eye.
Digital photography is generally harsher and brighter than film, with higher contrast and less exposure range. The look is a bit colder. It is also less forgiving than old-fashioned film. Film has a softer, pleasanter look. Yet with experience, you will find light and environments that work well in digital format.