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Graphics and Images (Graphics: Raster/Bitmap, Vector (Comparison between…
Graphics and Images
Graphics: Raster/Bitmap, Vector
Raster/ Bitmap are pixel images. Uses as grid of individual pixels where each pixel can be different colour or shade.
Vector graphics use mathematical relationships between points and the paths connecting them to describe an image.. Vector graphics composed of paths.
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Anti-Aliasing
Anti-aliasing is the application of subtle transitions in the pixels along the edges of images to minimise the jagged effect. Specifically used to better Bitmap images
Vector File extensions - .ai, .eps, .ps, .pdf, .svg, .swf
Raster Graphics has a RGB percentage of how much each pixel is coloured/ contribution. E.g - R = 93%, G = 9%, B =93%
General image File extensions: .gif, .fpg, .tiff, .psd, .raw
Colour depth/pixel depth
The number of bits per pixel on a computer monitor to represent a specific colour. The more bits per pixel, the higher colour variety and quality of the monitor.
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Deep colour supports 30, 36, and 48 bits per pixel accross 3 RGB colours.
2-bit colour depth values example -Binary code of 00,01,10,11. Colours are white, light grey, dark grey, and black
Bitmaps are defined by a rectangular mesh of cells (pixels). Each pixel holds 2 parameters - the number of pixels, and information content (colour depth) per pixel
Indexed colour is a more economical way of storing colour bitmaps (wihtout used 3 bytes per pixel). As with 8 bit grey bitmaps each pixel has one byte associated with it only now the value in that byte is no longer a colour value byt an index into a table of colours - palette or colour table
Dithering
Common application is to more accurately display graphics containing a greater range of colours than the hardware is capable of showing
Without dithering, the colours in the original image might simply be 'rounded off' to the closest available colour - resulting in a new image (poor representation)
Dithering takes advantage of the human eyes tendency to mix two colours in close proximity to one another
Converting a pixel = checking is a the colour is closer to black (0) or white (255) and relate it accordingly.
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Error Diffusion
Error Diffusion is an algorithm the makes a note of the 'error' in its conversion specifically that the gray pixel we have forced to black/white was actually 96 (wor whatever) steps away from black/white.
When moving to the next pixel, the error diffution algorithm adds the error of the previous pixel to the current pixel
If the next pixel is 96 and the algorithm adds the error of 96 from the previous pixel then tha result is 192 which means that its actually closer to 255 - so make it white!
The eror in this case is -63 because 192 is 63 less than 255 which is the value this pixel was forces to
When we finish the processing the line of an imafe, the error value is discarded and started again in the next line with a initial value of 0.
Disadvantages
if you have a very similar block of colour, you only push the error to the right, all the fots end up being in the same place.
LEads to funny lines of dots, 'lines of speckles'
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Since an image has a horizonal and vertical dimensions, better to push error value in both directions
8-bit Gray level images
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Image resolution - refers to the number of pixels in a digital image. Higher resolution = better quality
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Text
Unformatted (plain text), Formatted (rich text -fonted), hypertext (internet text)
Unformatted text
Unicode 1991 - developed by Xerox Palo Alto Research center (PARC) and Apple. Aim was to uniform character encoding. Now supported by microsoft, IBM, Adobe.
ASCII (1960), 8 bit code. 1977 it became ISO646 latin or european ASCII
Formatted Test - MS word, Tables, columns, underline, fonts, size, italic etc.
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24-bit colour images
Full RGB colour requires the intensities of 3 colour components to be specified for each and every pixel. It is common for each component intensity to be storesd as an 8-bit integer, so each pixel requires 34 bits to completely and accurately specify its colour. Image formats that store a full 24 bits to describe the colour of each and every pixel are therefore known as 34 bit colour images