F

This is Pixel (xmax,ymax)

Figure 1.14 Each pixel in a digital image has an "address" corresponding to its place in the image and the location of a photosite on the detector. The first pixel to be read from the detector is pixel (0,0) and the last is pixel (xmax,ymax). The image shown here is 16 pixels wide by 12 pixels high.

amounts of light organized by their angular positions relative to the optical axis of the camera. At any given location, the intensity of the image corresponds to the amount of light coming from some particular direction. Detectors break the image into thousands or millions of discrete areas, each represented by a pixel in the resulting digital image.

Pixel means picture element. Pixels are to digital images what photosites are to CCDs. A pixel may correspond to a photosite on the CCD, or if the chip is binned, a pixel may correspond to two or more photosites on the CCD. Each pixel in an image has three key properties:

The x-axis location is the pixel's location in the coordinate that is clocked more rapidly from the CCD. By custom, the x-axis is displayed horizontally on computer screens. It may also be called the i-axis, or the sample axis.

The y-axis location is the pixel's location in the coordinate that is clocked more slowly from the CCD. By custom, this axis runs vertically on computer screens. It is sometimes called they-axis, or the line axis.

The numerical value of a pixel (its pixel value) is encoded in bytes stored on the computer's hard disk. Pixel value is a property of pixels, just as mass is a property of matter. Pixel value can be expressed in different units of measurement, just as mass can be measured in grams, atomic mass units, etc. In raw images, where the pixel has obtained its numerical value directly from the output of the CCD

Image Aspect Ratio = 0.75 Image Aspect Ratio = 1.00 Image Aspect Ratio = 1.33

Pixel Aspect Ratio = 0.75 Pixel Aspect Ratio = 1.00 Pixel Aspect Ratio = 1.33

Figure 1.15 Aspect ratio is defined as width divided by height. For images, the width of the entire image is divided by its entire height. For pixels, the width of a single pixel is divided by its height. The wider the image or pixel is, relative to its height, the greater is its aspect ratio.

camera's analog-to-digital converter, the units of pixel value are ADUs (analog-to-digital units) or DN (data number).

ADUs can later be converted into pixel values expressed in units of electrons, ergs/cm2/sec., or any other physical unit of measurement you want the pixels in your images to have.

In color images, the pixel value is usually expressed as numerical values of the three additive color primaries: red, green, and blue. These RGB triads may be encoded as 8-bit integers (256 gray levels), as 12-bit integers (4096 gray levels), or 16-bit integers (65,536 gray levels), depending on the camera and the intended use for the image.

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