Flashcards in Computer Systems (Data Representation) Deck (18):
How are positive numbers represented in a Computer
They are represented in binary
128 64 32 16 8 4 2 1
1 0 0 0 0 1 1 1
What decimal number is represented in binary by 10000111?
How are real numbers represented?
Real numbers must be able to store decimal numbers the floating point system is used.
Explain how the floating point system works?
The Mantissa dictates the precision of numbers and the Exponent dictates the range
What is the mantissa in a floating point system?
The number of bits allocated to the Mantissa dictates the precision of a real number. More bits to the Mantissa leads to greater precision. Less bit leads to less precision.
What is the exponent in a floating point system?
The number of bits allocated to the Exponent dictates the range of a real number. More bits to the Exponent leads to greater range. Less bit leads to less range.
What is Extended ASCII?
Extended ASCII is one way to represent a character set. Extended ASCII code uses 8 bits to represent a character meaning that you can represent up to 256 different characters.
What are printable characters (ASCII)?
Printable characters are those that you will be able to see on screen. They have an 8 bit ASCII code. Examples are: A, s, !, @
What are control characters (ASCII)?
Control Characters are those that do not appear on screen but that carry out a task. They have an 8 bit ASCII code. Examples are:
Shift, Delete, Backspace, F2, Ctrl
What are bit-mapped graphics?
Bit Mapped graphics are made up of a 2D array of pixels. Every single pixel is saved. JPEG, PNG and GIF are bit mapped graphic formats.
What talking about colour depth for graphics, what is bit depth?
Every pixel is stored as a binary code. Bit depth is the number of bits used to store each pixel. A bit depth of 8 bits allows the pixel to be one of 256 colours, a bit depth of 16 bits allows for 65,536 colours and a bit depth of 24 bits allows for 16, 777, 216 colours. The higher the bit depth the larger the file size but the more colour available.
What is the resolution of an image?
Resolution is the total number of pixels in an image.
E.g. A resolution of 800 x 600 would create 480,000 pixels
What are vector graphics?
Vector graphics are NOTstored as individual pixels. Instead a description of attributes is used to create an object/shape. E.g. for a circle the attributes might be: cx (centre x), cy (centre y), rx (radius x), ry (radius y), fill, line. The computer uses the attributes to create shapes.
Vector graphics usually have smaller file sizes than bit
mapped graphics as you don’t need to store every pixel.
Name and describe four differences between bit-mapped and vector graphics
Scaling – Bit Mapped could be pixelated, vector would retain quality
Editing –Every pixel can be edited for fine detail in bit
mapped graphics, in vector, fine detail is harder to edit as you can only change individual attributes
Layering – Bit maps don’t let you layer shapes, whereas vectors do
File Size –bit mapped usually larger as every pixel is stored, whereas only attributes are stored in vector
With regard to vector graphics, what is a rectangle and how would it be stored?
Rectangle is a type of polygon but given the frequency of its use, most vector graphic file formats support a specific rectangle object. Squares could be created using either the rectangle or polygon objects.
Attributes: x, y, fill, line, height, length. x and y define the top left corner position
With regard to vector graphics, what is an ellipse and how would it be stored?
Ellipse objects are like circles, but you can alter the radius of the X co-ordinate so that it is a different value to that of the Y co-ordinate. This allows for the creation of oval shapes rather than circles.
Attributes: cx and cy define the centre, rx and ry the radius. Fill and line.
With regard to vector graphics, what is a line and how would it be stored?
The line object allows for the creation of lines. More complex lines with different points can be created using an object called a polyline.
Attributes: x1 and y1 define the start of the line, x2 and y2 define the end of the line. Line is used for the colour of the line. Fill IS NOT NEEDED for lines.