INTRODUCTION TO MATLAB PART4 Further GRAPHICS

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INTRODUCTION TO MATLAB PART4- Further GRAPHICS

• UNIVERSITY OF SHEFFIELD
• CiCS DEPARTMENT
• Deniz Savas Mike Griffiths
• JANUARY.2007

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PART 4TOPICS

• Handle Graphics
• Basic 3D Graphics
• Animation and Movies
• Displaying Bit-Mapped Images
• Visualisation aids with camera lighting and
  transparency

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Anatomy of Matlab Graphics

• Handle Graphics
• Animations

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Handle Graphics

• All Matlab graphics output is created in units of
  graphics objects with associated properties and a
  tree structured hierarchical dependency. User can
  manipulate these objects by changing their
  properties. The following diagram shows all the
  possible Matlab Graphics Objects and their
  hierarchy.

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Graphics Objects
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Graphics Objects

• The Root Contains everything
• Figure Individual Graphics Window
• Uicontrols User interface icons usually created
  by GUIDE utility.
• Axes defines mapping from real coordinates to
  screen coordinates
• Image A Matlab image consists of a data-matrix
  and possibly a colormap vector.
• Light Defines the position and color of light
  sources. These effect patch and surface objects
• Line, patch, rectangle self explanatory
• Surface A surface object is the 3D
  representation of matrix data where the element
  values are assumed to contain the z-coordinates.
• Text Character strings drawn on the figure. (
  labels etc. )

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Querying and Setting Object Properties

• Value get( object_handle, Property Name )
• set(object_handle,Property Name ,newvalue)
• Special symbol gca refers to the current axes
  object. get(gca) returns all its properties.
  Having found out what the property names are a
  subsequent set(gca , Property Name, newval )
  can be used to change a given property.
• Best way of familiarising is by using the
  property editor after a graph is drawn.
• Similarly gcf for Current Figure Object can be
  used
• Most other objects handles have to be obtained
  during the creation by using the function in the
  form handle function( )
• For example h plot( X, Y )

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Viewpoint

• Matlab allows us to re-define the viewing
  direction of the eye for 3D plots.
• This direction is defined by two terms namely
• Azimuth the angle with the y axis
• and
• Elevation angle with the x/y plane.

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view position and camera

• az elview ---gt return the current eye
  location in two scalars az and el.
• view( az , el ) ---gt set eye location.
• view(3) ---gt set to default 3D view
• el90 directly above -90 directly below.
• Camera Toolbar
• In the Figure Window, select the View-gtCamera
  Toolbar option. This will display a set of icons
  which gives full control to the camera position
  that controls the view.

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Animations with Matlab

• There are two distinct methods for creating
  animations
• By means of movies ( useful for complex
  pictures)
• By using the erase or xor mode of graphics and
  drawing and redrawing on the same graph.

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Matlab Movies

• Create the movie as a set of captured frames that
  can be displayed one after the other thus
  creating the effect of a movie.
• Commands are getframe and movie
• Example
• The following code captures the fast forrier
  transforsm of a series of step functions plots
  them and stores the plotted output in a structure
  named M which contains the bit-map data ( as type
  uint8 matrix and the colour-map
• for k 116
• plot( fft(eye(k16) ) )
• axis equal
• M(k) getframe
• end
• and the captured frames can be played back by
  typing movie(M)

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Animation by using the erase modes

• Techniques used by Matlab for drawing or
  redrawing a graphics object is determined by that
  objects EraseMode property. By default all
  objects EraseMode properties are Normal. This
  means that when any one of a Matlab Graphics
  Objects property that effects its visibility
  changes, Matlab erases that object and redraws it
  while taking care of all the 3D hidden
  surface/line aspects.
• This is why when you use the property editor
  to edit a Matlab Graph it gets redrawn
  automatically.
• However this behaviour can be altered by
  setting the EraseMode property of an object to
  one of
• None Do not erase the object when it moves or
  alters.
• Background Erase the object by redrawing it in
  the background colour
• Xor Erase only the object by Exclusive OR ing
  the graphics area with the objects pixels.

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Practice Session 13 Animation

• In the examples/animation directory, there is a
  script called makemov.m
• View this script and run it to save a movie
  matrix and replay the saved movie by using the
  movie command.
• In the same directory study and run the script
  named animateroot
• Study the scripts animpeaks1 and animpeaks2
  noting the use of the set function to update the
  graphics. Use the profiler to compare the two
  scripts

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Matlab Images

• Graphics features of Matlab we have seen so far
  were related to creating of images by mostly
  vector graphics techniques. We are now going to
  study the manipulating and displaying of
  previously captured images.
• Whatever the format, fundamentally images are
  represented as two or three dimensional arrays
  with each element representing the colour or
  intensity of a particular pixel of the picture.
• It would be perfectly valid to represent such
  image data as ordinary ( double precision) Matlab
  Matrices but the memory required to store a say
  1000 by 1000 image will 8 Mbytes which is too
  extravagant.
• As most image pixel data will be accurately
  representable by 8bits a Matlab data type named
  uint8 ( unsigned integer) is normally used for
  image data handling. This reduces the memory
  requirement to 1/8th !

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Matlab image Types

• A Matlab image consists of a data-matrix and
  possibly a colourmap matrix. The following three
  different image types are used
• Indexed Images
• Intensity Images
• RGB (TrueColour) Images

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Indexed Images

• These are stored as a two dimensional array of
  image data a colourmap matrix.
• The colour-map matrix is a m-rows by 3 columns
  matrix with each of the rows representing a
  colour defined by the three R,G,B components
  (ranging 0.0 to 1.0) of that colour. The image
  data contains indexes to this colour map matrix.
• The colormap is usually stored with the image and
  saved/loaded by the imwrite/imread functions.

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Intensity Images

• Image is a 2 dimensional Matrix whose each
  element is scaled by Matlab to produce a colormap
  index. The colormap index is an m by 3 array as
  in the indexed images, although this colourmap
  index is used during display it is not stored as
  part of the image as it can always be deduced
  from the data. These image forms are normally
  used for gray-scale type images where only the
  intensity is important.

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RGB Images

• Sometimes known as Truecolor images the data is
  stored as an n-m-3 image. I.e. m by n with 3
  planes. These 3 planes represent the R,G and B
  components of the pixel respectively. There are
  normally 8 bits allocated to the representation
  of each colour making it 2(38)
  22416Million possible colours.
• There is no colormap array for RGB images as all
  the colour information is contained in the data
  matrix.

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Handling Graphics Images

• Reading/Writing Graphics Images
• imread , imwrite
• load , save ( if only the image was saved as a
  MAT file)
• Displaying Graphics Images
• image
• imagesc
• Utilities
• imfinfo
• ind2rgb

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Practice session-14

• Find out information about the image file named
  sunset.jpg in the top level of the exercise
  directory by using the imfinfo function.
• Read this image into Matlab
• Display this image on the screen
• Edit the image figure and investigate its
  properties.

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THE END