Image representation.pptx

Introduction to Computer Science CS101.3 Lecture #11 From Last Week Computer Storage Structure Optical Disk  Image Representation  Computer-generated images can be stored in several different formats and different resolutions.  All computer...

Introduction to Computer Science CS101.3 Lecture #11 From Last Week Computer Storage Structure Optical Disk  Image Representation  Computer-generated images can be stored in several different formats and different resolutions.  All computer files such as numbers, words or graphics are stored in digital formats  When representing images what computer do is translate the image into digital code for storage and then interpret the file back into an image for display Digital Image Sources  Digital Cameras  Scanned Film & Photograph  Digitalized TV Signals  Computer Graphics  The Internet  Pixel  Computer graphics often involves with pixels  A pixel is one of the very small dots creating the image on your computer screen  Arranging pixels in certain patterns produces the illusion of color  A single pixel is one byte of information  Pixels and Pixel Values  Pixel – an element of the 2D image array  The most common pixel format is the byte image  In byte image number is stored as an 8-bit integer giving a range of possible values from 0 to 255.  Typically, zero is taken to be black and 255 is taken to be white  Digitalizing Images Images are digitized using a two-step process 01. Sampling the continuous tone image 02. Quantizing pixels Sampling Images Quantization Quantization Example  Types of Images Pixel Values  Binary Images ( Pixel Values = 0,1 )  Grayscale Images ( Pixel Values = 0 – 255 )  Color Images Each Pixel has three color components for example (red, green, blue ) or RGB Each color component is 0 - 255  Image Resolution  Resolution refers to the number of pixels in an image  Resolution is sometimes identified by the width and height of the image as well as the total number of pixels in the image.  For an example, an image that is 2048 pixels wide and 1536 pixels high ( 2048 x 1536 ) contains 3,145,728 pixels or 3.1 Megapixels  Image Resolution 68 x 104 136 x 208 272 x 416 Less Detail More Detail Less storage More storage Story of a Digital Image  Storing Digital Images  Digital images are converted to files for storage and transfer  The file type is a special format for ordering and storing the bytes that make up the image  File types or formats are not necessarily compatible  You must often match the file type with the application  Storing Digital Images File Types  GIF ( Graphic Interchange Format )  JPEG (Joint Photographic Experts Group)  PNG ( Portable Network Graphics)  BMP  How many bytes to store an Image Assume that we have an image that is 500 x 500 pixels in size Total Resolution = 250,000 pixels Binary Image ( 1 bit / Pixel ) = 31,250 bytes Grayscale Image ( 8 bits / Pixel ) = 250, 000 bytes Color Image ( 24 bits / Pixel ) = 750,000 bytes  Task 01 Assume that we have an image that is 400 x 600 pixels in size Find the number of resolution How many bytes need to store the binary image? How many bytes need to store the grayscale image? How many bytes need to store the color image?  Revision A magnetic disk have 12 platters, 5000 tracks on each surface and 20 sectors per track. The capacity of a sector is 3KB 1. Find the capacity of a track 2. Find the Capacity of a surface 3. Find the capacity of the total HDD 4. Find the capacity of a cylinder