Image synthesis, analysis and transmission

These are three parts of computer image processing: synthesis creates an image, analysis extracts information from an image, and transmission moves an image from one place to another.

Image synthesis

Image synthesis is the generation of an image from non-image data, such as a mathematical description, a data set or a model. Images may be produced by:

• Dynamic synthesis: the picture is created by a program on demand and can change with time, for example a graph of a function, a medical visualisation, a user interface or a game scene.
• Static synthesis: a stored picture is produced once, such as a designed drawing or a rendered 3-D scene.

Techniques include drawing primitives (lines, circles, polygons), 3-D modelling with lighting, shading, texture mapping and rendering. Used in computer-aided design, simulation, animation and visualisation.

Image analysis

Image analysis takes an image and finds what is in it. The aim is to get a description rather than a new picture. Stages:

1. Pre-processing to remove noise.
2. Segmentation of the image into regions and edges.
3. Feature extraction such as area, shape, position, colour, texture.
4. Recognition / classification of the objects by matching with models.

Examples: OCR, fingerprint and face identification, tumour detection in X-rays, robot vision, satellite image interpretation.

Image transmission

Digital images are large (a 1024 x 768 true colour image has about 2.4 MB), so they must be compressed before sending over a network. Important ideas:

• Compression with JPEG, GIF or PNG to reduce size.
• Progressive transmission: a coarse low-resolution version is sent first and detail is added step by step (interlaced GIF, progressive JPEG), so the user sees the picture early.
• Error protection and suitable protocols for reliable delivery.

Used in the web, fax, telemedicine, satellite imaging and video conferencing.

 Data/model --synthesis--> Image --analysis--> Description
                              |
                        transmission
                              v
                         Remote user