Kuliah 6

ImagePokok bahasan:

Introduction to computer graphicVector and bitmapImage compression and manipulationWeb graphicImage processingFile format

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Introduction to Computer Graphics

Computer graphics: The software and hardware technologies used in a computer system to create, modify and display still images stored in a digital form

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Bitmapped Graphics and Vector Graphics

In bitmapped graphics, the image is modelled by an array of pixel values.

In vector graphics, the image is stored as a mathematical description of a collection of individual lines, curves and shapes making up the image.

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Bitmapped Graphics

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Vector Graphics

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More About Vector Graphics

A curve is still a curve, even at 20,000 feet. Vector graphics can be sized and otherwise transformed without an inkling of quality loss.

You can get pretty pictures in small packages. Vector images depend on the complexity of the vector objects, not the size of the illustration

Vector images are independent — resolution independent, that is. Vector image has no built-in resolution

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Terminology

‘graphics’ reserved for vector graphics, and

‘images’ used to mean bitmapped images

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Bitmapped Editing and Files

Software Files

Adobe Photoshop .psd, .pict, .bmp, .tiff, Corel .gif, .jpg, .png

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Vector Editing and Files

Software Files

Adobe Illustrator .ai, .pdf, .eps, .swf, Adobe Freehand .wmf, .dxf

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Bit Depth

Bit-depth is used for the number of bits used to represent the color information in each pixel

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Maximum Number of Colors Possible for Image Type and Bit Depth

Image type Color depth # Colors possible

24 bit (True Color) 24 bits/pixel 16.7 million colors 16 bit (Hi Color) 8 bits/pixel 65 thousand colors Indexed 256 Color 8 bits/pixel 256 colors Indexed 16 Color 4 bits/pixel 16 colors Gray Scale 8 bits/pixel 256 shades of gray Scale 4 bits/pixel 16 shades of gray Monochrome 1 bit/pixel Black or white

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A = The number of bits in the graphic = [(x • y pixels) x (bit-depth)] B = Number of bytes = A/8 and C = Number of kilobytes (KB) = B/1024 x pixels wide, and y pixels high

For example, the file size of a 640 by 480 picture of 256 colors is calculated as follows: A = (640 X 480) X 8 = 2,457,600 bits B = 2,457,800/8 = 307,200 bytes C = 307,200/1024 = 300 KB

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Resampling Images

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Nearest Neighbor

This method is fast and provides for the smallest file size, but it is less precise and therefore of the lowest quality.

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Bilinear

Considered a medium-quality method, it works by averaging the color of the pixel above, below, and to the right and left of each pixel.

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Bicubic

This method is the slowest but most precise. It provides a smoother transition between pixels but also increases the contrast between pixels to reduce blurriness.

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Bicubic Smoother

Like Bicubic, but provides an even smoother transition between pixels and therefore increases the amount of blurriness. A good method to use when upsampling images.

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Bicubic Sharper

Also similar to Bicubic, but applies less anti-aliasing and therefore less blurriness as well. This is a good method when downsampling an image.

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Compression—JPEG

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Compression—GIF

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Reducing the Size of Image Files

The dimensions of the graphic (wide and high) The bit depth of the graphic or the number of colors used in the graphic The compression used

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Resolution

Dots per inch (dpi) for printed outputSamples per inch (spi) for scanned input

Pixels per inch (ppi) for images viewed on a computer display

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Resolution in Monitors

800 x 6001024 x 7681920 x 1440

> 54 ppi> 72 ppi> 133 ppi

Pixel per InchResolution

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Slices

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Anti-aliasing

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