Chapter 1 – Imaging

1.1 Seeing invisible things

Learning Outcomes

  • Images can be formed with many kinds of signals, including ultrasound and all regions of the electromagnetic spectrum
  • Images can be recorded electronically by microsensors; an example is the charge-coupled device (ccd); such images are composed of discrete picture elements – pixels
  • Images on the atomic scale can be recorded by scanning methods; an example is the scanning tunnelling microscope (STM)
  • The resolution of an image is the smallest distance over which a change can be seen

Lesson 1

Objectives: To be able to look at an image through the eyes of a physicist, and beginning to think about what the image is of, how it was formed and why the image is important to is. To think how frequency, wavelength and speed are important in imaging.

Activities:

Begin with 10S Examples of images in Physics either off the CD as an individual/feeding back exercise, or using the Powerpoint as a whole class discussion.

Any discussion should focus on e-m wavelengths, resolutions, and imaging system.

20D Electronic image capture can add to the experience.

Out of class:

Piglet / Pooh / Christopher Robin
Read p1-4 and box on p4
10S: Speed, frequency and wavelength / Q 1-4, p9 / 30X: Different kinds and uses of images
Q 5,6 p9

Lesson 2

Objectives: To consolidate previous lesson by checking understanding, introducing the STM and formalising pixels and resolution. This leads on to the next section on information in images

Activities:

30D Distance measurement with ultrasound can be used to remind students of v=f and s=dt. Go through 10S from homework.

Use the AS book to check understanding of STM and CCD (p10-11)

Write definitions of resolution and pixel, with examples. Q1-6, p5.

Out of class:

Piglet / Pooh / Christopher Robin
20E Large and small distances and times / Q1-5 p12 / 60S SEM image of Velcro

1.2 Information in images

Learning outcomes

  • Images can be stored as an array of pixels, each defined by a number; the amount of information stored = number of pixels ´ bits per pixel.
  • Images can be smoothed by suitable averaging; images can be sharpened by identifying edges; images can be enhanced by increasing contrast or by false colouring.
  • Quantities that cover a large range of values can usefully be displayed on a logarithmic ('times') scale. Prefixes for scientific units are chosen at multiples of 1000.
  • 1 bit of information contains 2 choices (0 or 1); 1 byte of information contains 8 choices (256 = 28 alternatives); information I provides N = 2I alternatives

Lesson 3

Objectives: To see how images can be altered by smoothing, noise reduction, contrast and edge enhancement.

Activities:

Briefly show pupils how to use Scion image and discuss noise reduction, smoothing and edge detection (p17).

Split class into groups and ask each to try two of

50S Image processing: The surface of Mercury

60S Image enhancing: Volcanoes on Io

70S Medical uses of x-ray images

80S Medical uses of ultrasound images

100S Mapping the South Atlantic sea floor

Out of class:

Prepare a short presentation on the analysis tools used to be given to the rest of the class next lesson.

Lesson 4

Objectives: To be able to describe in terms of individual pixels how to smooth, reduce noise and detect edges in images.

Watch presentations of image processing tasks.

40S Smoothing pixels using mean and median, Q5 p18

Out of class:

Piglet / Pooh / Christopher Robin
Check ‘You have learned’ boxes up to p18 for understanding so far. / 80S The Horsehead Nebula / 70S Image processing by brightness and contrast control
50X How was this image enhanced?

Lesson 5

Objectives: To be able to do calculations involving the amount of information in images.

Read p13-15 and introduce information in images, bits and bytes and image size.50O, 60O, 70O, 80O, 90O, 100O, 110O Display materials on the above.

120S How big are your computer files? Answer Q 1-4, 6 p18

Out of class:

Piglet / Pooh / Christopher Robin
110S Bits and bytes in images / 90C, 100C, Comprehension exercises / 120S, Logarithms and powers
130C Comprehension exercise

1.3 With your own eyes

Learning outcomes

  • The eye is like an intelligent video camera, sending out a stream of processed signals. It detects edges and movement.
  • A converging lens adds a constant curvature to light falling on it. The curvature added is the power of the lens.
  • Power of lens = 1 / f = 1 / v – 1 / u (Cartesian sign convention)
  • Magnification = height of image / height of object
  • Light takes the same time to travel on all paths from a point on the source to the image via the lens (or mirror).

Lesson 6

Objectives: To know that he eye is like an intelligent video camera, sending out a stream of processed signals. It detects edges and movement.

Activities:

Begin with a series of optical illusions and relate them to how the eye and brain process information being received. 20D A collection of visual illusions is a good place to start. Some of these are available on OHT (120O, 130O, 140O). 130D Grey step and 140E The intelligent eye both add to the experience.

Look at the eye is some detail using the AS book (p19-21) and 150D Models of the eye.

The next lesson will look at image formation, so do 60D Image in mid air and 180D Where are parts of an object in its image as an introduction.

Out of class

Piglet / Pooh / Christopher Robin
Read p 19-23 / 140S Response of human eye to differences in brightness

Lesson 7

Objectives: To know that a converging lens adds a constant curvature to light falling on it. The curvature added is the power of the lens.Power of lens = 1 / f = 1 / v – 1 / u.

Activities:

Begin with 200D Focussing water ripples as a visual demo, showing 160O and 170O as additional representations of waves.

Follow this with 170E Converging lenses: power and focal length, using class results to arrive at the lensmakers equation. Show 200O Where object and image are to be found to finish off.

Out of class

Piglet / Pooh / Christopher Robin
Read p 23-25, including the boxes
Q 1,2,4 p26 / Q 3,5,6 p26 / Look at 210O The lensmakers equation

Lesson 8

Objectives: To consolidate the lens equation, sign conventions and manipulating formula.

Activities:

Experiment 190E A converging lens adds curvature 1/f can now be tried. This uses the equation and sign convention, so these must have been met previously. Include magnification in doing this experiment

The Excel file 130S Lens action of a spreadsheet is a good extension for groups who want more practice at testing the lens equation

Out of class:

Piglet / Pooh / Christopher Robin
150S Cameras and eyes (essential!) / 160C Satellite imaging