Multimedia

Bit-map images

• Bit-map images are made up of pixels; the image is stored in a two-dimensional matrix of pixels.

• A pixel is a smallest element in a image, its color is represented by three component intensities such as red, green, and blue. (RGB)
• The image resolution is the product of the width multiply with the height of the image.

Colour depth and RGB

Online RGB

https://www.rapidtables.com/web/color/RGB_Color.html

• Colour depth is the number of bits used to indicate the color of a pixel.
• Normally, we use 24 bits to represent the color of a pixel.
• For example
  • #FF 00 00 represents primary colour red
  • #00 FF 00 represents primary colour green
  • #00 00 FF represents primary colour blue
  • #FF 00 FF represents fuchsia

File header

• File header is a set of bytes at the beginning of a bitmap file which identifies the file and contains information about the coding used.
  • file type (e.g. .png)
  • file size
  • image resolution
  • colour depth
  • type of compression being used.

Bit-map images keywords

• Colour depth: the number of bits used to represent one pixel.
• Bit depth: the number of bits used to represent each of the red, green and blue colours
• Image resolution: the number of pixels in the bitmap file defined as the product of the width and the height values.
• Screen resolution: the product of width and height values for the number of pixels that the screen can display.
• File header: a set of bytes at the beginning of a bitmap file which identifies the file and contains information about the coding used.

Bit-map Image

Bit-map images are made up of ; the image is stored in a two-dimensional matrix of .

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Bit-map Image

The is the product of the width multiply with the height of the image.

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Bit-map Image

is the number of bits used to indicate the color of a pixel.

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Bit-map Image

is a set of bytes at the beginning of a bitmap file which identifies the file and contains information about the coding used.

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Calculating bit-map image file sizes

• The file size = image resolution x colour depth.

TIP

1. The image has a resolution of 400 x 300 pixels, and a colour depth of 8 bits per pixel.
2. 400 x 300 x 8 = 960000 bits

Bit-map Image

The image has a resolution of 100 x 100 pixels, and a colour depth of 24 bits per pixel. The file size of this image is bytes?

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Vector graphics

Online Editor

https://vectorink.io/app/

Example

• Vector graphics are images that use 2D points to describe lines and curves and their properties that are grouped to form geometric shapes.

• Vector graphic: a graphic consisting of drawing objects defined in a drawing list

• Drawing object: a component defined by geometric formulae and associated properties

• Drawing list: contains one set of values for each drawing object

• Property: defines one aspect of the appearance of the drawing object

Vector graphics

Vector graphics are images that use 2D points to describe and their properties that are grouped to form .

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Vector graphics

A vector graphic will contain a which contains one set of values for each

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Bit-map images VS Vector graphic images

Factors	Vector graphic images	Bit-map images
Made up	geometric shapes	tiny pixels of different colours
Edit	change each of the geometric shapes	edit each of the pixels
File size	less file size	larger file size
Reality	not realistic	very realistic
Scaling up	no loss of quality	fuzzy
Format	.svg, .cgm, .odg	.jpeg, .bmp, .png

Image

Whose quality will not be lost when scaling up?

A.

Bit-map images

B.

Vector graphics

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Sound

• Sound is an analogue value; this needs to be digitised in order to store sound in a computer.
• This is done using an analogue to digital converter (ADC).
• To convert the analogue data to digital, the sound waves are sampled at a given time rate.

• Analogue data: data obtained by measurement of a physical property which can have any value from a continuous range of values
• Digital data: data that has been stored as a binary value which can have one of a discrete range of values
• Sampling: taking measurements at regular intervals and storing the value
• Sampling resolution: the number of bits used to store each sample
• Sampling rate: the number of samples taken per second

Sound

Sound is an analogue value; this needs to be in order to store sound in a computer. This is done using an analogue to digital converter (). To convert the analogue data to digital, the sound are at a given time .

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• Standard sampling rate is 44 100 samples per second.
• In audio CDs, each sample is recorded as a 16-bit integer.

Sound

A 10-second sound clip will be recorded. The sound will be sampled 16000 times a seconds. Each sample will be stored using 16 bits. This size of this file is bytes?

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Calculating audio file sizes

• The file size = sampling rate x sampling resolution x seconds.

TIP

1. A 32-second sound clip will be recorded. The sound will be sampled 16000 times a seconds. Each sample will be stored using 8 bits.
2. 16000 x 8 x 32 = 4096000 bits

Video

• They are often referred to as DV (digital video) cameras; they store compressed photo frames at a speed of 25MB per second – this is known as motion JPEG.
• When recording video, the frame rate refers to the number of frames per second (FPS).

Video

When recording video, the refers to the number of frames per second (FPS).

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Activity

A software designer needs to incorporate images into her software to add realism.

• Describe the differences between bit-map images and vector graphics.

• Explain what she needs to consider when deciding between using bit-map images and vector graphics in her software.