Lesson Objectives

• Explain the representation of an image as a series of pixels represented in binary

• Explain the need for meta data to be included in the file such as height, width and colour depth

• Discuss the effect of colour depth and resolution to the size of an image

Starter

• In your booklets is a completed cross work.

• Create the clues to go along with the answers!

• You have 10 minutes

BITMAP IMAGES

Pictures must be shown on a screen or a printer as a series of dots, known as pixels.

Each of these pixels is stored as a series of bits. Each bit corresponds to a part of the image.

Images stored in this way are called bit-mapped image files.

The more dots in a given area, the better the quality.

This is called the resolution of the picture.

Monochrome• A monochrome bitmap will store a 1 for a black pixel and 0 for a white pixel (or vice-versa depending on the encoding protocol).

This image could be represented by the following 35 binary digits (5 bytes):

00100 01010 01010 10001 11111 10001 00000

It would also be necessary to store the dimensions of the image.

Task 1:

• In your booklets complete the bitmap images.

• Ensure you convert each image into BINARY and HEX

Bitmap Images

• When a bit-mapped image is enlarged, the pixels enlarge too.

• This produces a jagged, blurred image.

Coloured Bitmaps• If this “A” image was in colour, using a colour palette of 256 possible shades, each pixel would need to translate to a value between 0 and 256 (8 bits).

More colours• It is common for colours to be recorded by quantity or Red, Green and Blue (RGB) and this is stored using 3 bytes per pixel

• An 8 bit byte has 256 variants, so 256 different shades of Red (green or blue) can be represented.

• With a 3 byte number system there are 256 x 256 x 256 =16.8million possible colours.

Interactive colour wheel

• http://www.mathsisfun.com/numbers/color-wheel-interactive.html

Resolution• Resolution refers to the number of pixels in an image.

• The higher the resolution, the more pixels and the bigger the file size.

High resolution: 1288 kB Low resolution: 67 kB

Computers need to be able to store, display and manipulate photographs and graphical images. However, computers can only handle binary data (in the form of 1s and 0s) so it is imperative that all images must be stored in a digital format. For this to happen an image is broken down into dots of individual colours, each one known as a pixel. Each pixel is assigned a colour. If there are few pixels, they will be large therefore the image will appear blocky and crude. The more pixels contained in an image the clearer it becomes as more colours can be used with a better transition between each colour. This is known as picture resolution. Up to 256 different shades of red, blue and green can be displayed giving a total of 16.8 million possible colours.

OCR GCSE Computing © Hodder Education 2013 Slide 12

Metadata

• Metadata is data about data.• Images from digital cameras are stored with a considerable amount of metadata that records information such as…• the height;• the width;• the colour depth;• the resolution;• camera used;• exposure details;• when the image was created;• who owns the copyright;• contact information.

Various websites let you read the metadata about digital photos. • Picture EXIF Info• Resolution Unit => Inch• Flash Used => No Flash• Make => Olympus Imaging Corp.• Model => SP700• xResolution => 72 dots per ResolutionUnit• yResolution => 72 dots per ResolutionUnit• Software => Version 1.0• File Modified Date => 2010:08:24 10:22:46• YCbCr Positioning => Datum Point• Exposure Time => 1/400 sec• DateTime => 2010:08:24 10:22:46• DateTime Digitized => 2010:08:24 10:22:46• Exposure Bias => 0 EV• Aperture => f/3.3• Light Source => Unknown or Auto• Focal Length => 10.3 mm• Height => 2112 pixels• Width => 2816 pixels• Scene Capture Type => Directly Photographed• Compress Scheme => Jpeg Compression

Fill in the gaps

• A/A* = 9/10 out of 10• B – 8+ out of 10• C – 7+ out of 10