Data Representation Flashcards
Arithmetic shifts
Multiplying
To multiply by two, all digits shift one place to the left
To multiply by four, all digits shift two places to the left
To multiply by eight, all digits shift three places to the left
Arithmetic shift
Dividing
to divide by two, all digits shift one place to the right
to divide by four, all digits shift two places to the right
to divide by eight, all digits shift three places to the right
What is Colour depth?
The number of bits determines the range of colours. This is known as an image’s
colour depth.
To add colour, more bits are required for each pixel.
For example, using a colour depth of two - two bits per pixel - would allow four possible colours such as:
11 - white
10 - light grey
01 - dark grey
00 - black
What is Bit colouration
Each extra bit squares the range of colours that are available:
1 bit per pixel (0 or 1) - 2 possible colours
2 bits per pixel (00 to 11) - 4 possible colours
3 bits per pixel (000 to 111) - 8 possible colours
4 bits per pixel (0000 to 1111) - 16 possible colours
8 bits per pixel (00000000 to 11111111) – 256 possible colours
16 bits per pixel (0000000000000000 to 1111111111111111) - 65,536 possible colours
Image colour depth
The more colours an image requires, the more bits per pixel are needed.
Image file size calculation
The image height in pixels.
The image width in pixels.
The colour depth per pixel.
Image file size calculation example
Example - an image of height 200, width 400, colour depth 16 bits
200 × 400 = 80,000
80,000 × 16 = 1,280,000 bits
1,280,000 bits ÷ 8 = 160,000 bytes
160,000 ÷ 1000 = 160 kilobytes
Result: 160KB
Resolution
The resolution of a bitmap image is a way of describing how tightly packed the pixels are.
In a low-resolution image, the pixels are larger and, therefore, fewer are needed to fill the space. This results in images that look blocky or pixelated.
An image with a high resolution has more pixels, so it looks a lot better when it is enlarged or stretched. The higher the resolution of an image, the larger its file size will be.
What is metadata?
Data about data, eg photo image files have data about where the photo was taken and which camera took the picture.
What data does metadata include?
file type
date created
author.
The height and width of the image - this defines how many rows and columns the pixels are to be arranged in.
The resolution.
The colour depth,
Describe the process of sound sampling
Sampling is a method of converting an analogue sound signal into a digital signal
• At specific intervals a measurement of the amplitude of the signal is taken .
measures the level of sound many times per second
Sample rate is the number of times each second that each of those time slices, or samples,
are recorded.
What are the three factors affecting sound?
Sample rate
Bit depth
Bit rate
What is sample rate?
Sample rate is the number of samples recorded in any given period of time.
The higher the sample rate, the closer the recorded signal is to the original.
Sample rate is measured in
hertz (Hz).
What is bit depth?
refers to the number of bits used to record each sample.
Just as with images, the higher the bit depth, the more accurately a sound can be recorded, but the larger the file size.
Typical bit depths are 16 bit and 24 bit.
What is bit rate?
measure of how much data is processed for each second of sound.
Sample rate × bit depth
As with sample rate, the higher the bit rate, the better the quality of the recorded sound.
