Keywords Bitmap Vector Pixels Resolution Metadata Data Representation

Keywords Bitmap, Vector, Pixels, Resolution, Metadata. Data Representation Images

Type of Digital Image Objectives ADVANCED: Understand how a digital image is made up and be able to recognise the affect changing the resolution has on an image. EXPERT: Understand how a computer displays coloured images using binary and rgb values. BITMAP: The page is divided into an invisible grid and each pixel is assigned a colour. VECTOR: Drawn by following a set of mathematical instructions. Draw a circle, radius: 6 pixels, centre: 10, line thickness: 1 pixel. METADATA: Certain information must be defined for the bitmap image, this is called METADATA (or data about data) Size of grid Width: 20 pixels, Height: 20 pixels A 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.

Using Pixels to Create a Binary Image We call this pixelated. Objectives ADVANCED: Understand how a digital image is made up and be able to recognise the affect changing the resolution has on an image. EXPERT: Understand how a computer displays coloured images using binary and rgb values. This image is represented in Binary in 1 s and 0 s, as they are the binary digits. The black squares are represented as 1’s and the white squares are represented as 0 s. Would the image change if we used a 16 x 16 grid? Why?

Data Representation Objectives ADVANCED: Understand how a digital image is made up and be able to recognise the affect changing the resolution has on an image. EXPERT: Understand how a computer displays coloured images using binary and rgb values. The number of pixels we use is known as the resolution. So, what affect does increasing the resolution have? On average, computer screens are 1, 366 x 768 pixels which means we can display images from the computer using 1, 049, 088 pixels! Colour depth How many bits will be used to store the colour for each pixel in the grid. The greater the colour depth: The more realistic colours. The more data needs to be stored and the larger the file size on disk. 1 bit allows 2 different values 2 different colours (b&w) 2 bit allows 4 different values 4 different colours 3 bit allows 8 different values 8 different colours . . . 8 bit allows 256 different values 256 different colours 24 bit allows 16, 777, 216 different values 6, 777, 216 different colours

Direct Colour Objectives ADVANCED: Understand how a digital image is made up and be able to recognise the affect changing the resolution has on an image. EXPERT: Understand how a computer displays coloured images using binary and rgb values. R FF 00 00 80 96 00 FF 80 FF G FF 00 00 FF FF 80 00 B FF 00 FF 96 80 00 00 α 00 00 00 By mixing the appropriate amount from each of the three colour channels you can get a variety of colours. There is a 4 th channel, called the alpha channel which handles transparency What gets stored for each pixel is just a combination of each channel. FFFFFF 00 means the pixel is white 96008000 means the pixel is lilac 8 bit gives 256 colours Real life colour needs 15 or 16 bits 24 -bit or “truecolor “gives over 16. 7 million colours.

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Questions Objectives ADVANCED: Understand how a digital image is made up and be able to recognise the affect changing the resolution has on an image. EXPERT: Understand how a computer displays coloured images using binary and rgb values. 1. In your own words, explain how a bitmap image can be represented in Binary and how the resolution of an image can change. 2. What does pixelated mean? 3. What is Metadata and why does it need to be included in the file? 4. Discuss the effect of colour depth and resolution on the size of an image. 5. Which three colours are used to make all three colours on a computer? 6. Discuss direct colour and explain how colour is stored this way.