Unit 2.6 Data Representation - PowerPoint Presentation

1. Unit 2.6 Data RepresentationLesson 3 ‒ Images

2. ObjectivesUnderstand how a bitmap graphic is made up of individual pixels Explain how each pixel is represented in binaryUnderstand that the number of bits per pixel determines the number of available colours for an imageExplain the need for image metadataExplain the relationship between file size and image resolution

3. Type of Digital ImageTwo main types:BITMAP - The page is divided into an invisible grid and each pixel isassigned a colourVECTORDrawn by following a set ofmathematical instructionsDraw a circleradius: 6 pixelscentre: 10, 10line thickness: 1 pixel

4. Bitmap (or Raster) imagesBitmap images are made up of PICture ELement or PIXELSA pixel is the smallest identifiable area of an imageEach pixel is a single colour and is given a binary value which represents that colour e.g. 11000000 might equal RedA pixel’s colour can be changed by changing this value

5. Image resolutionResolution is the concentration of pixels within a specific areaThe area is defined by the image width and height in pixels e.g. 3264x244872dpi = screen resolution300 dpi = print quality resolution 1x1 2x2 5x5 10x10 25x25 50x50 72x72 300x300

6. Creating an ImageEach pixel is given a binary valueEach value represents a different colourUsing one bit per pixel allows only 2 values, 0 and 1 1 = Black, 0 = White0000100000000110000000111010000111101100111110111000001010001111111111011111111000111111100000000000

7. Increasing the number of coloursMore bits per pixel = more colour combinations1 bit = 2 Colours2 bits = 4 Colours3 bits = 8 Colours4 bits = 16 ColoursHow many bits per pixel required for 256 colours?00 = 11 = 01 = 10 = 101010101010110111110111010101010111010101010111010111110101111111010101010101

8. Colours and resolution vs File SizeHow does the number of colours affect file size?How does the size of the image affect file size?20 pixels20 pixels8 colours

9. Colour or bit depthEach pixel can represent a finite number of coloursA pixel is attributed a number of n bitsThe number of combinations (2n) dictates the bit depth and therefore the number of colours that can be representedA higher bit depth gives a greater range of colour and a better quality of image8 bits per pixel = 28 = 256 colours16 bits per pixel = 216 = 65,536 colours24 bits per pixel = 224 = 16,777,216 colours

10. Variation in qualityChanging the colour depth of an image will affect the number of colours it can display, as shown below: 2 Colours 4 Colours 8 Colours 16 Colours 256 Colours 16.7m Colours

11. PBM monochrome imagesStore image dimensionsChange ‘colours’ by changing binary values

12. Colour values181ml126ml61ml

13. Looking at colour codesColour values of individual pixels are expressed as denary RGB values and in hexadecimal. Why not in binary in this instance?RGB (Red, Green and Blue) values range between 0-255. How many bits are required for 256 variations of each?How many bits altogether?In 32-bit colour what are the last 8 bits for?

14. Why file sizes don’t always add upDucksBMP: 1000 x 750 pixels24 bit colour depth = 16m coloursWhat is the file size in bytes and MB?Why is there a difference of 2,800 bytes?

15. Image metadataMetadata is data about dataIt is information other than image data that is stored with a fileThis will include:Colour depth in bits per pixelResolution (Height and width in pixels)Date createdAuthorHow big is the DucksJPG file? Why is this different?

16. What have you learned?A bitmap graphic is made up of __________________Each _______ is represented in binaryThe ________________________ determines the number of available colours for an imageImage _________ holds data about the image such as ___________________________________________The greater the _________ of the image, the greater the file size

17. PlenaryA bitmap graphic is made up of individual pixels Each pixel is represented in binaryThe number of bits per pixel determines the number of available colours for an imageImage metadata holds data about the image, such as colour depth, resolution, date created, authorThe greater the resolution of the image, the greater the file size

18. MetadataCertain information must be defined for the bitmap image, this is called METADATA (or data about data)Size of gridWidth: 20 pixels Height: 20 pixelsA term for 'data about data'. In other words metadata describes the structure of the data file and is usually located right at the start of the file.When a media player opens the file it looks for the metadata which describes the format of the file e.g. the file type, how many horizontal pixels are there, how many vertical pixels and the colour depth of the file. The media player reads the file and correctly displays the image.

19. Direct ColourThere is a 4th channel, called the alpha channel which handles transparencyWhat gets stored for each pixel is just a combination of each channelEg FFFFFF00 means the pixel is white96008000 means the pixel is lilac8 bit gives 256 coloursReal life colour needs 15 or 16 bits24-bit or “truecolor “gives over 16.7 million coloursBy mixing the appropriate amount from each of the three colour channels you can get a variety of coloursRGBα FFFFFF00 00000000 0000FF00 80009600 96008000 00FF0000 FFFF0000 80800000 FF000000

20. PlenaryComplete the binary representation for the following:

21. Plenary - AnswerComplete the binary representation for the following:1 0 0 1 1 0 0 10 1 0 0 0 0 1 01 0 1 0 0 1 0 10 1 0 1 1 0 1 00 0 1 0 0 1 0 00 1 0 1 1 0 1 01 0 1 0 0 1 0 10 1 0 0 0 0 1 0