Daily Archives: August 3, 2015

Introduce Raster Image : Digital Video and HD

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In modern times, digital image and digital video are more important and more active. We use on many device movie theaters, camera on mobile phone, digital TV, DVD, VCD, Computer, digital printer and other. A digital image is represented by a rectangular array (matrix) of picture elements (pixels). Pixel arrays of several image standards are shown, with their counts of image columns and rows. In a grayscale system each pixel comprises a single component whose value is related to what is loosely called brightness. In a color system each pixel comprises several components (usually three) whose values are closely related to human color perception.

Historically, a video image was acquired at the camera, conveyed through the channel, and displayed using analog scanning, there was no explicit pixel array. Modern cameras and modern displays directly represent the discrete elements of an image array having fixed structure. Signal processing at the camera, in the pipe-line, or at the display may perform spatial and/or temporal resampling to different formats.

The pixel array is for one image is a frame. In video, digital memory used to store one image is called a framestore, in computing, it’s a framebuffer. The total pixel count in an image is the number of image columns NC (or in video, samples per active line, SAL) times the number of image rows NR (or active lines, LA) The total pixel count is usually expressed in megapixels (Mpx).

In video and in computing, a pixel comprises the set of all components necessary to represent color (typically red, green and blue). In the mosaic sensors typical of digital still cameras (DSCs) a pixel is an color component individually, the process of demosaicking interpolates the missing components to create a fully populated image array. In digital cinema cameras the DSC interpretation of pixel is used, however, in a digital cinema projector, a pixel is a triad.

The value of each pixel component represents brightness and color in a small region surrounding the corresponding point in the sampling lattice.

Pixel component values are quantized, typically to an integer value that occupies between 1 and 16 bits and often 8 or 10 bits – of digital storage. The number of bits per component, or per pixel, is call the bit depth. (We use bit depth instead of width to avoid confusion, the term width refers to the entire picture)