WPCN?  
      2 .     B       P    Z       .     Courier 10cpi  #| x           Times (Scalable) CG Times Italic (Scalable) HP LaserJet III                      HPLASIII.PRS x 
   @   ,\,42X@ USUK  3'                                          3'Standard                                  6&                                          6& Standard    rJet III   _ K  +                                          #  Xw     P 7[hXP#  2   	    `  "   b      X  W  +Courier 10cpi CG Times (Scalable)  "  m+O6^;C]ddCCCdCCCCddddddddddCCȲY~~wCN~sk~CCCddCYdYdYCdd88d8ddddJN8ddddYYdYC dd  ddd   C dddddd ddd8 YYYYYY~Y~Y~Y~YC8C8C8C8ddddddddddYdddddsdYYYYYYYd~Y~Y~Y~YddddddddC8C8C8C8oN d~8~8~8~8~8dvddddJJJkNkNkNkN~8~8~8dddddddYYY  d~8dJkN~8dddddC     dd   C      CCWxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxNd ddCYQQddddddFddddF CC hhd44ddzzddd woo     Ch      d     F"Ȑdh             d岲  dCCȐzȲxCddodȐȅdCdYdsȐ]Ȑ ȐȧzȐ       Uw                                                                                                 ŐdȐ      Y   Y                           C   C   C   C                                                               ΐz~o  zoY~NYdYC8YooYdYzsdzd d~YYzozzzzNd88YYYzYz z zz CCddddd          dd         zzzzzzzzzzzzzzzzzzzNNNNNNNdddddddddddddddddddd888888888888YYYYYYYYYYYYYYYYYYYzzzzzzzzzzzzzzzzzzzzC  s  ~CzdYC x ? x x x ,    wx 6X   @ 8; X@|  8 w C ; ,  [hXw     P 7XP x / c 8 1 ,  c     P 7P6z - b 8 1 , " b &_  x $&7X 2               
   V      "  m+O6^18MSS888S8888SSSSSSSSSS88Jxir{icx{8Aui{x`xoZi{xxxl888SS8JSJSJ8SS..S.SSSS>A.SSxSSJJSJ8 SS  SSS   8 SSSSSS SSS. xJxJxJxJxJorJiJiJiJiJ8.8.8.8.{SxSxSxSxS{S{S{S{SxSxJ{SxSxSxS{S`SxJxJxJrJrJrJrJ{SiJiJiJiJxSxSxSxSxSxS{S{S8.8.8.8.z]A uSi.i.i.i.i.{S{c{S{SxSxSxo>o>o>ZAZAZAZAi.i.i.{S{S{S{S{S{SxxSlJlJlJ  {Si.{So>ZAi.xSxS{SxS{S8     SS   8      88WxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxNxxxS SS8JDDSSSSSS;SSSS; 88 VVS++SSffSSxS c]]     8V      S     ;"xxSxWxx             S唔  S88xfxxxxxxxxxxx8SxS]SxoS8SxJS`xlxxxxxxxxxxMxxxx xxofx       Gc                                               xxxx                                                  xxxSxxxx   xx   xJ   xxxxJ   xxxxx   xxx   xxx   xxx   xxxxxxxxxxxxxx     x   xxxxxx    xxxxxxxx8   xxx8   xxx8   xxx8   xxxx   x                                                   x   xxxx   xxxxfi]  f]oJiAlJ{SxJ8.uJo]]{JoSxJxf`SfS SiJxJofx]ffffAS..JJJfJf f ff 88SSSSS          SS         fffffffffffffffffffAAAAAAASSSSSSSSSSSSSSSSSSSS............JJJJJJJJJJJJJJJJJJJffffffffffffffffffff8  `  xi{8xxfSJ8 x "  m+O6^18PSS888S8888SSSSSSSSSS88Sffoxf`xx8Jo]oxfxfS]xff]]888SS8SSJSJ.SS..J.xSSSSAA.SJoJJAJSJ8 SS  SSS   8 SSSSSS SSS. fSfSfSfSfSooJfJfJfJfJ8.8.8.8.oSxSxSxSxSxSxSxSxS]JfSxSxSxS]JxSfSfSfSfSoJoJoJoJxSfJfJfJfJxSxSxSxSxSxSxSxS8.8.8.8.SJ oJ].].].].].oSofoSoSxSxSofAfAfASASASASA].].].xSxSxSxSxSxSo]J]A]A]A  xS].oSfASA].]J]JxSxSxS8     SS   8      88WxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxNxxxS SS8SMMSSSSSS;SSSS; 88 SSS..SSffSSxS ZSS     8S      S     ;"xxSxSxx             S唔  S88xfxxxxxxxxxxx8SfS]SxoS8SxJS`xlxxxxxxxxxxMxxxx xxofx       Gc                                               xxxx                                                  xxxSxxxx   xx   xJ   xxxxJ   xxxxx   xxx   xxx   xxx   xxxxxxxxxxxxxx     x   xxxxxx    xxxxxxxx8   xxx8   xxx8   xxx8   xxxx   x                                                   x   xxxx   xxxfff]  f]oJfA]JxSxJ8.oJo]]oJoSxJxffSfS S]J]Joff]ffffAS..JJJfJf f ff 88SSSSS          SS         fffffffffffffffffffAAAAAAASSSSSSSSSSSSSSSSSSSS............JJJJJJJJJJJJJJJJJJJffffffffffffffffffff8  `  ffx8x]fSJ8 xCourier 10cpi CG Times (Scalable) CG Times Italic (Scalable) CG Times Bold (Scalable)  2 #      Z      <       "  m+O6^;C]ddCCCdCCCCddddddddddCCȲdzN`zoȐCCCddCdoYoYFdo8Co8odooYNCodddYdddCdd  ddd   C dddddd ddo8 dddddϐYYYYYN8N8N8N8oddddooooddoddddzodddYYYYoYYYYddddddooN8N8N8N8r` o888N8ooodd┐YYYoNoNoNoNCCCooooooȐdYYY  o8oYoNCddodoC     dd   C      CCWxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxNd ddCdUUddddddFddddF CC ssd44ddzzddd ~oo     Cs      d     F"Ȑds             d岲  dCCȐzȲxCddodȐȅdCdYdsȐ`Ȑ ȐȮzȐ       Uw                                                                                                 ŐdȐ      d   d                           C   C   C   C                                                               ΐzo  zoYNYYYN8YooYdYzzdzd dYYzozzzzNY88YYYzYz z zz CCddddd          dd         zzzzzzzzzzzzzzzzzzzNNNNNNNYYYYYYYYYYYYYYYYYYYY888888888888YYYYYYYYYYYYYYYYYYYzzzzzzzzzzzzzzzzzzzzC  z  NzdYC x ? x x x ,    wx 6X   @ 8; X@  8 w C ; ,  [hXw     P 7XP x / c 8 1 ,  c     P 7P6 z - b 8 1 , " b &_  x $&7X   7 z C ; , = sXz _    p ^7X  3 m = 6 ,  #{&m     P 7&P  2 p = 6 , = h&p _    p ^7& "  m+O6^6=U\\===\====\\\\\\\\\\==Qs~sm=Gsizbsw===\\=Q\Q\Q=\\33\3\\\\DG3\\\\QQ\Q= \\  \\\   = \\\\\\ \\\3 QQQQQz~QsQsQsQsQ=3=3=3=3\\\\\\\\\\Q\\\\\i\QQQ~Q~Q~Q~Q\sQsQsQsQ\\\\\\\\=3=3=3=3fG \s3s3s3s3s3\m\\\\zDzDzDbGbGbGbGs3s3s3\\\\\\\wQwQwQ  \s3\zDbGs3\\\\\=     \\   =      ==WxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxN\ \\=QKK\\\\\\A\\\\A == __\00\\pp\\\ mff     =_      \     A"\_             \壣  \==px=\\f\z\=\Q\iwU zp       Nm                                                                                                 ń\      Q   Q                           =   =   =   =                                                               ΄psf  pfzQsGwQ\Q=3QzffQz\Qpi\p\ \sQQzpfppppG\33QQQpQp p pp ==\\\\\          \\         pppppppppppppppppppGGGGGGG\\\\\\\\\\\\\\\\\\\\333333333333QQQQQQQQQQQQQQQQQQQpppppppppppppppppppp=  i  s=p\Q= x "  m+O6^6=U\\===\====\\\\\\\\\\==\zzpGXzpfzz===\\=\fQfQA\f3=f3f\ffQG=f\\\Q\\\=\\  \\\   = \\\\\\ \\f3 \\\\\QzQzQzQzQG3G3G3G3f\\\\ffff\\f\\\\pf\\\QQQQfzQzQzQzQ\\\\\\ffG3G3G3G3iX fz3z3z3zGz3fff\\ψQQQfGfGfGfGz=z=z=ffffff\zQzQzQ  fz3fQfGz=\\f\f=     \\   =      ==WxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxN\ \\=\NN\\\\\\A\\\\A == ii\00\\pp\\\ sff     =i      \     A"\i             \壣  \==px=\\f\z\=\Q\i~X zp       Nm                                                                                                 ń\      \   \                           =   =   =   =                                                               ΄pzf  pfzQzGzQQQG3QzffQz\Qpp\p\ \zQQzpfppppGQ33QQQpQp p pp ==\\\\\          \\         pppppppppppppppppppGGGGGGGQQQQQQQQQQQQQQQQQQQQ333333333333QQQQQQQQQQQQQQQQQQQpppppppppppppppppppp=  p  zGp\Q= x 2 5    $  \  (    C,  	  1   "  m+O6^+1DIIr111I1111IIIIIIIIII11Aj\dm\Wjm19g\mjTjbO\mjjj_111II1AIAIA1II))I)rIIII69)IIjIIAAIA1 II  III   1 IIIIII III) jAjAjAjAjAbdA\A\A\A\A1)1)1)1)mIjIjIjIjImImImImIjIjAmIjIjIjImITIjAjAjAdAdAdAdAmI\A\A\A\AjIjIjIjIjIjImImI1)1)1)1)kQ9 gI\)\)\)\)\)mImWmImIjIjIjb6b6b6O9O9O9O9\)\)\)mImImImImImIjjI_A_A_A  mI\)mIb6O9\)jIjImIjImI1     II   1      11WxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxNjjjI II1A<<IIIIII4IIII4 11 LLI&&IIZZoIIjI WzzQQ     1L      I     4"jjIjLjj             I傂  I11jZjjjjjjjjjjx1IjIQIjbI1IjAITjr_jjjjjjjjjjDjjjj jjzbZrj       >W                                               jjjj                                                  jjjIjjjj   jj   jA   jjjjA   jjjjj   jjj   jjj   jjj   jjjjjjjjjjjjjj     j   jjjjjj    jjjjjjjj1   jjj1   jjj1   jjj1   jjjj   j                                                   j   jjjj   jjjjZ\Q  ZQbA\9_AmIjA1)gAbQQmAbIjAjZTIZI I\AjAbZjQrZZZZ9I))AAAZAZ Z ZZ 11IIIII          II         ZZZZZZZZZZZZZZZZZZZ9999999IIIIIIIIIIIIIIIIIIII))))))))))))AAAAAAAAAAAAAAAAAAAZZZZZZZZZZZZZZZZZZZZ1  T  j\m1jjZIA1 x ? x x x ,    wx 6X   @ 8; X@  8 w C ; ,  [hXw     P 7XP x / c 8 1 ,  c     P 7P6 z - b 8 1 , " b &_  x $&7X   7 z C ; , = sXz _    p ^7X  3 m = 6 ,  #{&m     P 7&P	   2 p = 6 , = h&p _    p ^7& j ) W 1 + ,  ۏW     P 7P6  1 k = 6 , " W"&k &_  x $&7&XO  A % ! ,  JA     P 7JP "  m+O6^6=X\\===\====\\\\\\\\\\==\ppzpi=Qzfzpp\fppff===\\=\\Q\Q3\\33Q3\\\\GG3\QzQQGQ\Q= \\  \\\   = \\\\\\ \\\3 p\p\p\p\p\zzQpQpQpQpQ=3=3=3=3z\\\\\\\\\fQp\\\\fQ\p\p\p\p\zQzQzQzQ\pQpQpQpQ\\\\\\\\=3=3=3=3\Q zQf3f3f3f3f3z\zpz\z\\\zpGpGpG\G\G\G\Gf3f3f3\\\\\\zfQfGfGfG  \f3z\pG\Gf3fQfQ\\\=     \\   =      ==WxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxN\ \\=\UU\\\\\\A\\\\A == \\\33\\pp\\\ b\\     =\      \     A"\[             \壣  \==px=\p\f\z\=\Q\iwU zp       Nm                                                                                                 ń\      Q   Q                           =   =   =   =                                                               pppf  pfzQpGfQ\Q=3zQzffzQz\Qpp\p\ \fQfQzppfppppG\33QQQpQp p pp ==\\\\\          \\         pppppppppppppppppppGGGGGGG\\\\\\\\\\\\\\\\\\\\333333333333QQQQQQQQQQQQQQQQQQQpppppppppppppppppppp=  i  pp=fp\Q= x "  m+O6^!%377bV%%%7b%%%%7777777777%%nbn1bOEKQEAOQ%+MEdQO?OI;EQOhOOG%%%77%17171%777V7777)+77O771171n% 77  777   % 777777 777 O1O1O1O1O1bIK1E1E1E1E1%%%%Q7O7O7O7O7Q7Q7Q7Q7O7O1Q7O7O7O7Q7?7O1O1O1K1K1K1K1Q7E1E1E1E1O7O7O7O7O7O7Q7Q7%%%%P=+ M7EEEEEQ7QAQ7Q7O7O7bOI)I)I);+;+;+;+EEEQ7Q7Q7Q7Q7Q7hOO7G1G1G1  Q7EQ7I);+EO7O7Q7O7Q7%     77   %      %%WnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxNOOO7 77%1--77a777bb7'7777b' %% 997bnn77CCTn7n7O7 A\\==b     %9      7  h   '"nnnnOOnnn7Onn9OObbnnn             7bbnnn  b7%%nnnnnOCnbOOOOOOOOOOx%n7O7=7bnOnI7%7O17?OVGnnOOOOOOOOOOnnnnn3nOOOOnnnnnnnnnnnnn nnnnnnOOnnnnnn\ICVnOn   nn    /A                                               OOOO                       nn          n        nn         nOOO7OOnOOnnn   OO   O1   OOOO1   OOOOO   OOO   OOO   OOO   OOOOOOOOOOOOOO     O   OOOOOO    OOOOOOOO%   OOO%   OOO%   OOO%   OOOO   O                                                   O   OOOO   OOOOCE=  C=I1E+G1Q7O1%M1I=d=Q1I7O1OC?7C7 7E1O1ICO=VCCCC+7111C1C C CC %%77777          77         CCCCCCCCCCCCCCCCCCC+++++++777777777777777777771111111111111111111CCCCCCCCCCCCCCCCCCCC%  ?  OEQ%OOC71% x 2     
  6   ^  :  -   `       L?   "  m+O6^!%577bV%%%7b%%%%7777777777%%nbn7bCCIOC?OO%1I=\IOCOC7=OC\C==%%%77%77171771O7777++71I11+171n% 77  777   % 777777 777 C7C7C7C7C7bII1C1C1C1C1%%%%I7O7O7O7O7O7O7O7O7=1C7O7O7O7=1O7C7C7C7C7I1I1I1I1O7C1C1C1C1O7O7O7O7O7O7O7O7%%%%Z71 I1=====I7ICI7I7O7O7hIC+C+C+7+7+7+7+===O7O7O7O7O7O7\I=1=+=+=+  O7=I7C+7+==1=1O7O7O7%     77   %      %%WnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxNOOO7 77%73377`777bb7'7777b' %% 777bnn77CCTn7n7O7 ;TT77b     %7      7  b   '"nnnnOOnnn7Onn7OObbnnn             7bbnnn  b7%%nnnnnOCnbOOOOOOOOOOx%n7C7=7bnOnI7%7O17?OVGnnOOOOOOOOOOnnnnn3nOOOOnnnnnnnnnnnnn nnnnnnOOnnnnnn\ICVnOn   nn    /A                                               OOOO                       nn          n        nn         nOOO7OOnOOnnn   OO   O1   OOOO1   OOOOO   OOO   OOO   OOO   OOOOOOOOOOOOOO     O   OOOOOO    OOOOOOOO%   OOO%   OOO%   OOO%   OOOO   O                                                   O   OOOO   OOOCCC=  C=I1C+=1O7O1%I1I=\=I1I7O1OCC7C7 7=1=1ICC=VCCCC+7111C1C C CC %%77777          77         CCCCCCCCCCCCCCCCCCC+++++++777777777777777777771111111111111111111CCCCCCCCCCCCCCCCCCCC%  ?  CCO%O=C71% x ? x x x ,    wx 6X   @ 8; X@  8 w C ; ,  [hXw     P 7XP x / c 8 1 ,  c     P 7P6 z - b 8 1 , " b &_  x $&7X   7 z C ; , = sXz _    p ^7X  3 m = 6 ,  #{&m     P 7&P	   2 p = 6 , = h&p _    p ^7& j ) W 1 + ,  ۏW     P 7P6  1 k = 6 , " W"&k &_  x $&7&XO  A % ! ,  JA     P 7JP
6P  @ % ! , " gJ@ &_  x $&7JXOO   O                                                   O   OOOO   OOOOCE=  C=I1Q7O1%M1I=d=Q1I7O1OC?7C7 7E1O1ICO=VCCCC+7111C1C C CC %%77777          77          
     
 # &m     P 7#{&P# 
     
 
















a% Section 1




a An Introduction to the BILKO Image Processing Software



















   "         p-p-p-                p-p-p-            q     a  z N    # c     P 7P# Marine and Coastal Image Data Module 3:`p"3 Introductory Tutorială  
    
 


   Y  # Xw     P 7[hXP# 
a INTRODUCTORY TUTORIAL:
   X r 
a THE BILKO IMAGE PROCESSING SOFTWARE
# &m     P 7#{&P# 

   S   a# Aim of Lessonă

To introduce the concept of image analysis and to demonstrate a series of operations by which
particular features of an image may be brought into prominence. 


   S  a$ Objectivesă

After completing this lesson, you should have learned to:

1)  load the BILKO software and digital images for analysis;

2)  select and apply the image analysis and modification routines of the BILKO 1.3 system;

3)  read the pixel value for a chosen coordinate; display and interpret the histogram of a loaded
image; carry out simple modifications of a look up table so as to enhance particular features of an
image; select the colours shown in an image; modify an image by selecting particular areas and by
zooming the display; plot a transect between chosen points on an image; apply a variety of filters to
a chosen image; combine images of a single scene, using data from one image to select, or otherwise
modify, what is shown of another; toggle rapidly between two images;

4)  call for help files when in doubt about any image handling procedure.


   T K a Background Information and Notational Conventionsă

BILKO is an image processing system developed for use with worksheets and lessons in
oceanographic applications of remote sensing.  Its routines may be applied to the analysis of any
image and include many standard image processing functions.  It is not however designed to compete
in power, speed and versatility with commercial image processing systems: it is a low cost toolkit
deliberately optimised to help students learn some of the techniques of remote sensing.

This tutorial is a revised version of the tutorial which was published in Module 2.  It has been revised
in response to the changes and additions incorporated in BILKO version 1.3 which is supplied on the
accompanying disks.  If you have worked through Module 2 you will be familiar with much of this
tutorial.  However, this tutorial supersedes that in Module 2 and is selfcontained.  Some menu
changes have occurred between Module 2 and Module 3.

To begin, you should familiarise yourself with all of the available options and the notation used by
following this demonstration.

To run the programs you require an IBM PC or close compatible, a colour monitor, VGA or EGA   (         p-@*@*@@  standard graphics capability and a 1.2 Mbyte 5" or 1.4 Mbyte 3" floppy disk drive.

All the files necessary to run this demonstration will be found on floppy disk 1.  If you have copied
the files to a hard disk you will find that they occupy about 800k of disk space.

In this lesson you are required to deal with file names and to make entries on the keyboard of your
computer.  So as to be explicit about how entries should be made the following typographic
convention is used throughout the tutorial.

   S  Keynames

   T H	 The names of keys are spelled out (for example, <ESCAPE>,<ENTER>,<CONTROL>) and appear in
small capital letters.  On your own keyboard the key caps may abbreviate the names or represent them
a little differently.

   S  Direction Keys

   T X The <DIRECTION> keys are the four arrow keys on your computer's keypad. The name of the
   T 0 individual <DIRECTION> key refers to the direction the arrow points: the <UP> key, the <DOWN>
   T  key, the <RIGHT> key, or the <LEFT> key.  Pairs of keys are sometimes denoted the <VERTICAL>
   T  keys and the <HORIZONTAL> keys.  You use the <DIRECTION> keys to move the selection, the
pointer, or the insertion point on your screen.

   S h What You Type

Anything you are required to type verbatim is printed in capitals.  For example, if you are asked to
   T  type a file called MYVUE.LUT, what you actually type is shown in capitals: MYVUE.LUT.  (In
practice it does not matter whether you type the letters in capitals or not).

   S y Menu Choice

In BILKO most entries are made by choosing an item from a menu.  The convention adopted here
   T  is that menu items are shown in bold face type as, for example, Display image and Histogram


   S  5a& Startupă

To begin the tutorial you must load and run the control programme.


   T ! Activity: `	`	   Type UNESCO13 <ENTER>"`	

   T r# Following a credit screen you will find you have access to a screen labelled Main Menu.  From this
point forward you control the processing of images from within the programme.


   S & a  The Main BILKO Menuă

   T ( The Main Menu is displayed as white text on a blue ground with just one of the 16 entries coloured
red.  The entries represent options, red indicating the one available for immediate selection.  When   \)        p-@*@*@@     T    the Main Menu is shown just 7 keys are active:

   T  1. <DIRECTION> keys: By using the direction keys, <UP> <DOWN> <LEFT> <RIGHT>, the red
highlight may be moved at will between the menu items.

   T 9 2. <ENTER>:  Pressing <ENTER> selects the option shown in red.

   T  3. <H>:  Pressing <H> displays a Help screen relating to the option shown in red.

   T  4. <ESCAPE>:  Pressing the escape, <ESCAPE>, key exits the programme and returns to DOS.

   T I	 After a selection has been made you may always return to the Main Menu by pressing the
   T "
 <ESCAPE> key.  The same key provides a return path from the Help screens. Note that Help screens
   T 
 provide an extensive on-line facility which is available at any time.  The <H> key activates a screen
which describes the option selected and/or the keys currently available for use.  Long Help screens
   T  may be scrolled using the <UP> and <DOWN> arrow keys.

   T Z Activity: `	`	   Familiarise yourself with the menu and keyboard by making some selections.  You
   T 2 will find that the <HORIZONTAL> keys move the red highlight between the columns
   T 
 while the <VERTICAL> keys move it up and down.  If you press <H> you will find
abbreviated descriptions of the different menu choices."`	

   T   X  X`	`	 Try one or more selections using the <ENTER> key.  You will find that most give
error messages or ask you to provide a file name.  This is because you have not yet
loaded an image.  You should be able to return to the Main Menu by using the
   T  <ESCAPE> key."`	

   T   X  X`	`	 Note that if you chance to use the <ESCAPE> key twice, you leave the programme
and must carry out the startup procedure once again."`	



   S  a Using the Menu Optionsă

To make use of the BILKO software it is necessary to provide an image on which to perform the
available operations.

   T : Activity: `	`	   Return to the Main Menu.  Select Load image and press the <ENTER> key.  A
green box will appear asking for a file name.  At this point type:"`	

   T !  X  X`	`	 EIRE4.DAT <ENTER>"`	

If you make a mistake in the filename the programme will not be able to find the file.  It will tell you
so and let you try again.  When a suitable file name has been entered, a menu showing the file size
appears.  The menu shows the following items: first line, last line, line sample, first pixel, last pixel,
pixel sample.  The values displayed are the default for that file ie. its actual size, and may be changed
if required.  In the case of EIRE4.DAT the file size displayed is 1, 256, 1, 1, 512, 1.  Press
   T ' <ENTER> to load the image described by these parameters.  If the displayed parameters result in a
line length greater than 512 pixels, or more than 256 lines to be displayed, the command will not be
   T [) accepted, and the parameters must be changed.  Enter <TAB> to move from line to line of the file   [)        p-@*@*@@     T    size menu.  To change a parameter enter the new values and use <SPACE> to delete any unwanted
   T   digits. If the <ENTER>  is accepted you should now see an Image loading message followed by a
   T  return to the Main Menu.  


With the programme running and an image loaded, you can begin to explore the capabilities of the
   T  BILKO software.  The remainder of this section introduces the items of the Main Menu one by one.

The items offered in the Main Menu are:
O  
     d d x                           
 ! d d x                O    	  
                Load image   	       Save image  
` 	              Load LUT   {
       Save LUT ` 	` 		              Load palette          Save palette ` 	` 	{
              Display image   ;
       Cursor ` 	` 	              Histogram          Filters ` 	` 	;
              Modify LUT          Multi image ` 	` 	              Modify image   [       Transect ` 		              Modify palette          Miscellaneous 	 [   

   S  1. Load image

   T K The Load Image option copies an image from disk into RAM and is an essential first action.  This
is what you did in the Activity above. When chosen, a green box will appear asking for the file name. 
At this point any image can be loaded. 

If you make a mistake in the filename, the program will not be able to find the file and will tell you
so and let you try again.  Because you may alter and choose the line and pixel coordinates, a large
diskfile image may be reduced to a suitable display size, the maximum dimensions being 512 pixels
by 256 lines.  For example if you have on a disk file an image of 1024 lines by 1024 pixels, set the
following line and pixel coordinate values to choose a subsampled overview to load and display:
 first line = 1, last line = 1024, line sample = 4
 first pixel = 1, last pixel = 1024, pixel sample = 2

These values extract a subsampled image which uses every fourth line and second pixel of the original
to give an overview.  To load a full resolution subimage of the original disk file, set the sample factor
to unity and choose first and last lines and pixels so that their difference is not greater than 256 or
512 respectively.  When the image has been loaded into RAM, you are returned to the main menu.
Note that this option does not display an image: it loads an image and makes it available.


   S T& 2. Display image

   T ( The Display image option allows you to display the currently loaded image on the screen.
   (        p-@*@*@@  Ԍ   T    Activity: `	`	  Choose Display image to display EIRE4.DAT.  You should see a false colour
thermal image of north east Ireland and the North Channel linking the Atlantic Ocean
and Irish Sea.  On the right hand side of the screen you will find a thermometer
indicating the relative temperatures of the displayed colours: black is lowest and white
highest.  The displayed image will stay on the screen until you press any key to
   T 9 return to the Main Menu.  Press any key.  Now the Main Menu appears."`	


   S  3.  Cursor

   T r The Cursor option allows the image coordinates, pixel value and colour value of any individual pixel
to be displayed.  All images are stored on disk in an 8-bit format, so the pixel value for each image
co-ordinate will lie in the range 0-255.  The relationship of these values to the physical measurement
will vary according to the type of image being displayed.

   T  Activity: `	`	   Select the cursor option now.  A yellow cursor appears on the screen and details of
its position and pixel value are shown at the bottom of the screen.  The cursor is
   T [ initially placed at (x, y) = (171, 85) in EIRE4.DAT and the pixel value at this point
is 146.  This corresponds to colour 9 in the look up table (LUT) which defines the
way in which each of the 16 displayable colours are assigned to a range of pixel
   T  values.  Use the arrow keys to move the cursor around the image.  Toggle the <CAPS
   T  LOCK> key to move in individual pixel steps or in pixel steps of 20.  Move the
cursor to the top left hand corner of the image, to the light green area (EGA display)
or midgrey (VGA display) represented as colour 10.  Move the cursor around in this
section and notice how the colour number does not change but the pixel value does. 
   T  Now exit from the cursor option: press <ESCAPE>.  This last observation leads to
the next item of this tutorial."`	


   S | 4. Load LUT

The final point of the last section is important: each colour or grey tone in an image covers a range
of pixel values.  Just what colour is used is determined by the way in which the look up table, LUT,
is mapped onto the pixel values. Detail in a particular feature may be brought out by mapping a
different range or 'stretch' of pixel values to different colours or grey tones.

   T d Activity: `	`	  Choose the Load LUT option and enter the file name EIRE4.STR.  Return to the
   T = Main Menu and choose Display image. Notice how the land areas are now shown
in black and that much more detail is shown up in the water areas.  Notice how the
thermometer showing the current LUT has been changed from the default LUT."`	

   T " Activity: `	`	   Restore the original stretch using the <ESCAPE> key.  Choose Load LUT and enter
   T w# the file name DEFAULT.STR.  Use Display image to show that the image has
returned to its initial condition."`	

The use of look up tables is an important aspect of image processing and will be treated again under
   T & the option Modify LUT. To appreciate what can be done however it is necessary first to introduce
   T ' the option called Histogram.

   b)         p-@*@*@@  ԌÙ
   S   5. Histogram

   T  The Histogram option displays a histogram showing the number, f(N), of pixels in the loaded image
having a given pixel value versus the set of values, N, a pixel can take.  By using left and right arrow
keys, a green line can be moved through the histogram, the corresponding frequency of the data value
in the image being displayed at the bottom.  The image statistics are displayed at the top of the
histogram.  The yellow line on the histogram indicates the mean value.  Notice that the histogram of
EIRE4.DAT is essentially bimodal.  The lower values represent land pixels and higher values, water
pixels.

   T I	 Question 1:   `	`	 Enter the Histogram option and use the left and right arrows."`	

   T 
          1.1:  `	`	 What pixel value is found most frequently in the lower peak of the histogram
displayed?"`	`" (answers will be found at the end of this lesson)

   T 
          1.2:  `	`	 What is the greatest number of pixels having any single value in the histogram
displayed?"`	


   S  6. Modify LUT

   T  The Modify LUT option contains a sub-menu offering three options:  Histogram equalization,
   T k Linear stretch and Manual stretch.  

   T  As in the Main Menu use of the arrow keys changes the option shown in red and the <ENTER> key
selects that option.  All options may be used to remap the current LUT to the pixel values.

   T  Histogram equalization is an automatic contrast stretch which allocates approximately equal areas
of the display to each of the 16 available colours or grey tones in the image.  This option gives a
good overview of the image, without revealing small scale image detail.

   T  Question 2:   `	`	 Execute the Histogram equalization option and look at the resulting image and
thermometer.  How does this stretch compare with EIRE4.STR loaded earlier?"`	

   T  Linear stretch allows you to choose two points between which a simple linear stretch is carried out. 
The lower point defines the pixel value below which all pixel values will be mapped to the lowest
value colour (black) and the upper point defines the pixel value above which all pixel values will be
mapped to the highest value colour (white).  Between these two points, the LUT is mapped linearly
to the remaining 14 colours.

   T " Activity: `	`	   Select Linear stretch: a histogram will be displayed.  Adjust the upper limit of the
   T x# stretch by toggling <CAPSLOCK> to ON and holding down left or right arrow keys
as appropriate; this will move the red, right hand cursor, through the histogram.  To
   T (% set the lower limit of the stretch toggle the <CAPSLOCK> key OFF and use the right
or left arrow keys to move the left, blue, cursor through the histogram.  Press
   T & <ENTER> when you are finished, and reply <N> when asked whether you want to
   T ' overlay the stretch.  Remember you can press <H> at any time to get help on what
to do."`	
   `)         p-@*@*@@  Ԍ X  X`	`	 View the results of the following stretches:"`	

 X  X`	`	  X 1.  Set limits at 0 and 60"
 X  X`	`	  X 2.  Set limits at 135 and 175"

These stretches show how important it is to use the correct LUT for detailed work.  In stretch 1, the
land is enhanced while the water is saturated: in stretch 2, the reverse is true.

   T  The Manual stretch option allows you to select the pixel values (or range) to which the colours will
be mapped so you can create your own LUT.  This option has possibilities beyond the needs of this
present tutorial.

   T !
 Notice that the result of exercising choice among the Modify LUT options is to produce screens of
   T 
 different types. Histogram equalization produces an image: Linear stretch gives a histogram with
   T  controls for selecting limits: and Manual stretch shows a histogram mapped against the palette
colours.


   S 4 7.  Modify palette

   T  If you are running BILKO 1.3 on a VGA display, the Modify palette option is not active because
   T  the default palette is 16 greys.  If you are running BILKO 1.3 on an EGA display Modify palette
   T  is active. Note: to obtain an EGA palette on the VGA, load EGA.PAL via the Load palette option. 
   T o To revert back to greys load VGA.PAL. Through the Modify palette option you may select the
colours used in an image.  Note that this is indeed a choice of colour: it does not alter the way in
which the pixel values are mapped to colours via the LUT.  With EGA.PAL you have a default
16-colour palette but you are free to change this and may choose any 16 colours from an available
64.

The option allows you considerable freedom to choose the colours used in images.  It will become
clear that a well-organised palette considerably enhances your ability to interpret the viewed image. 
   T 0 Together, the Modify LUT and Modify palette options give you complete control over how the
colours are mapped to pixel values and which colours are used in a particular mapping.

   T  If you are using an EGA palette when Modify palette is selected, you will see a screen composed
of a 2 x 2 subsampled current image (blank if no image has been displayed), the current palette shown
on the right of the screen, while three 'towers' representing the red green and blue weights of each
colour are shown at the centre.  Each colour may be set to have the value 0,1,2 or 3.  To change
   T   colour place the cursor slider on the palette tower using the <LEFT> and <RIGHT> keys and select
   T   a colour slot by using the <UP> and <DOWN> keys.  The RGB towers indicate the RGB weights
used to make the colour selected on the palette tower.  The displayed image also reflects the altered
   T " colours.  Press <ENTER> to save the new colours as the current palette.  Press <ESCAPE> to exit
and return the original palette.

   T *% Activity: `	`	 1.Load the EGA.Pal and select the Modify palette option and create your own
palette. Watch the changes in the image."`	

 X  X`	`	 2. Try to form a palette with a sense of progression in it -- the spectral colours
perhaps -- and see if you can identify pattern in the image."`	
   c)	         p-@*@*@@  Ԍ   T     X  X`	`	 3. Exit to the Main Menu and choose Modify LUT.  Select Manual stretch.  You
will now see the 16 slots displayed horizontally below a histogram.  The bands are
   T  of the variable length depending on the active LUT.  Now select Histogram
   T  equalization in the Modify LUT option and return to Manual stretch: you will see
your colours now as equal bands."`	

Note in the above exercises that the Help screen is always available to show you a way out of trouble.

   T  Question 3:  `	`	 Load EIRE4.STR using the Load LUT option and EIRE4.PAL using the Load
Palette option.  View the image.  What do you see?"`	

   T L	 Activity:  `	`	 Complete the exercise by returning to the original colour palette. Escape back to
   T $
 Main Menu: select the Load Palette option and load the file DEFAULT.PAL."`	


   S  8. Modify image

   T ] A blue sub-menu appears when the Modify image option is chosen and the Main Menu turns green. 
Choices from the sub-menu, as elsewhere, are made by moving the red highlight to the required entry
   T  and pressing <ENTER>.

   T  As the name suggests, Modify image provides options which alter the displayed image.  The options
   T  are: Subimage and Zoom.

   T H Subimage allows a subimage of the loaded image to be taken and subsequently treated as the
memory resident image, that is, the subimage is treated as a new image.  When finished, the sub   T  image created may be saved to disk via the Save image option.

   T  The Zoom option allows any user selectable section of the memory resident image to be temporarily
magnified.  When the zoomed image appears, a cursor is also presented so pixel values can be
investigated.



   S  9. Multiimage

   T k Selection of the Multiimage option causes a sub-menu to be offered. This has six options:
   T D Radiometric masking, Twoband ratioing, Scattergram, Image arithmetic, Toggle and NDVI. 
   T   As in the Main Menu use of the arrow keys changes the option shown in red and the <ENTER> key
selects that option.

The options of this sub-menu differ from those described earlier in that each requires the input of two
image filenames. Note that in BILKO 1.3, the multiimage functions must operate on two files of the
same dimensions, which should be no more than 512 pixels by 256 lines.

   T & Radiometric masking makes it possible to use a selected pixel range from one image to mask out
part of a second image.  This option is particularly useful when both visible and infrared channels
from the same scene are available.  In this case the visible image can be used to identify the land/sea
boundary and the information applied to the thermal image, where the boundary may be uncertain.
   g)
         p-@*@*@@  ԌThe programme requires the names of two files to perform the radiometric mask.  The first is that
of the file defining the mask, the second that of the image to be examined.

The maskdefining file is loaded into memory so that its histogram can be computed.  After the
second filename has been entered the histogram of the first is displayed.  Left and right pointers
   T 8 define the mask.  They can be moved along the histogram in the same way as in the Linear stretch
   T  function of Modify LUT.  All of the pixels, in the image defining the mask, which have a value less
than the value chosen by the left pointer or greater than the right pointer, define the mask.  The pixels
at the corresponding places in the masked image will be set to zero.  Below the histogram are
displayed the upper and lower ranges defining the mask, and the corresponding percentage of the
   T r image which will be masked.  Having selected the most appropriate mask the <ENTER> key is
selected.  The second image file is then read into memory and the mask applied.

   T 
 On completion, the program returns to the Main Menu.  To view the masked image select the
   T  Display image option.  Examination of the histogram of a masked image shows that the masked
values are ignored in the statistics and in subsequent stretches.

   T \ Activity:   `	`	 Use EIRE2.DAT as the masking file and EIRE4.DAT as the image file.  Try the
value 13 as the entry for the range to be masked.  You should see the required
masking of land data.  Try some stretches of the data to confirm that only unmasked
pixels contribute to the image statistics."`	
# &m     P 7#{&P# 
   T  The Twoband ratioing option performs a simple ratio on the data sets of any two image files.  This
   T m means the pixel value on row i and column j  of the first image, or numerator, is divided by the
   T G corresponding value on row i and column j of the second image, or denominator, assuming this
   T ! second value is non-zero.  The range of possible ratios lies between the values Rmin and Rmax where
   T  Rmax  is the ratio of the minimum value in the first image divided by the maximum value in the second
   T  image, and Rmin is either undefined or is the ratio of the maximum value in image one divided by the
smallest value in image two.  The upper limit is undefined in cases where the minimum value in the
second image is zero.

To display the values determined by the ratio option a linear stretch is applied to map the ratios onto
the range [0,255].  The mapping is established by selecting appropriate subranges of values in the
numerator and denominator. This is done by choosing a box region on the scattergram (see below for
an explanation of the scattergram) of the two images.  The numerator lies along the x-axis and the
denominator along the y-axis.  The two cursors  define the upper and lower limits of the mapping. 
   T o The top left cursor corresponds to Rmin and is mapped to zero, while the bottom right hand cursor
   T I corresponds to Rmax and is mapped to 255.  All ratios outside the range are mapped to zero or 255
respectively.  It should be remembered that any two boxes selected on the scattergram which have
   T   the same area and whose corresponding vertices lie on the family of lines y=x+c will generate
identical linear maps.  For completeness, the ratio of two zero pixels is set to 255.

   T # Having selected the most suitable range for the stretch <ENTER> is selected. On completion the
   T ]$ program returns to the Main Menu.  The ratio of the two images can be viewed by selecting the
   T 6% Display image option.

   T & The Scattergram option generates a two-dimensional representation of the information in any two
selected images.  In this the axes take values from zero to 255 and correspond to the possible pixel
   T ( values of each image file.  A point on the graph at the position (x,y) indicates that for some single   (        p-@*@*@@     T    position (a,b) in the image files the value x is taken in image 1 and y  is taken in image 2.  This
option allows the user to select a suitable subregion of interest for the scattergram.

   T  On completion the scattergram is displayed by pressing either  <ENTER> or the spacebar. The first
image can be reviewed or a new region of interest selected.

   T  The Image arithmetic option allows the user to perform simple arithmetic operations on two images. 
   T  After entering the filenames of the two images a coefficient box appears.  This box defines three
   T  coefficients a,b and c such that the output image is defined in terms of the input images A and B as:

   T u a output image = aA + bB + c .

   T '
 HINT:  set A=B or b=0 for single image arithmetic.

   T  On completion the program returns to the Main Menu, where the resultant image can be viewed by
   T  selecting the Display image option. 

   T c The Toggle option allows the user to view two files in a rapid flick or toggle mode to allow 
differences to be viewed and analyzed.  Enter the two filenames and press the spacebar to toggle.

   T  The NDVI (Normalised Difference Vegetation Index) option calculates the NDVI of two images based
on the following:


 `	`	  NDVI = 256 ' (image 1   image 2)
 `	`	   hh#   (image 1 + image 2)


   S  10. Transect

   T ] The Transect option allows a transect to be plotted between any two points on an image.  This is
shown on the screen as a graph of pixel values versus position along the line between the points.  To
define the end points of the transect two cursors are used.

Transects may be superposed by pressing the space bar when viewing one transect.

   T n Activity:  `	`	 Use the Help screen to guide you through the creation of a transect across the
land/water boundary in EIRE4.DAT.  Form a second transect across the front noted
previously."`	



   S ~# 11. Save image, Save LUT, Save palette

   T .% The three Save options have common elements which make it useful to describe them together.  Each
   T & of these options will be used after exercising the corresponding Modify option and is used to put a
record on disk of work which has been done on an image.

Save options are used, for example, after you have changed the look up table to suit some particular
requirement and wish to retain it for later use.  With the new LUT, the one currently active, select   h)        p-@*@*@@     T    Save LUT. You will then be asked to choose a file name.  Insert a name of up to 8 characters with
an extension of 3 characters.

Within BILKO the convention used is that the file extension for look up tables is STR, for example,
DEFAULT.STR and EIRE4.STR.  File extensions for images are DAT, for example EIRE4.DAT,
and for palettes are PAL, for example EIRE4.PAL.  All saved files have forced extensions as above. 
   T  This makes compatibility issues easier to program.  Note that when using the Load options, the
appropriate extension will be appended to a file name entered without extension: only then will the
search begin.


   S J	 12. Miscellaneous

   T 
 The miscellaneous menu offers options not included in the other menu classifications.  The DOS shell
allows you to exit temporarily to DOS to allow DOS commands to be executed before returning to
BILKO.  Some DOS commands may corrupt the image data stored in RAM so you should save any
work before proceeding.  For example it is possible to check the filenames in a directory without
exiting from BILKO.

   T  If you have a VGA display, the VGA mode allows you to display a 300 x 200 subimage of the
loaded file at full 8bit resolution.  The default palette is 256 grey levels but, if required, a new VGA
   T  palette may be loaded (see the box below): a prompt is offered during the option.  Press <ENTER>
at this point to retain the 256 greys.  The image currently loaded in RAM appears with a cursor to
identify the centre of the 300 x 200 subimage to be selected for display on the VGA.

E  
 ! d d x               
 A d d x     
   b     E  B
		[              
   S | VGA palette information

   T , In the VGA mode, you can enter new palettes if you wish.  These palettes have a different
format to the EGA ones.  Each screen colour is defined by a 4byte integer which specifies the
blue, green and red colour intensities.  The integer is formatted as:

most significant bit                                least significant bit

             zzzzzzzz zzBBBBBB zzGGGGGG zzRRRRRR

where z is set at 0, and B,G,R represent the bit values for blue, green and red intensities
respectively.  Therefore in the VGA256 mode the LUT has 256 entries each 4 bytes long so
   T   the palette consists of 1024 bytes.  This is the case for VGA256.PAL and REV256.PAL.
 B
		     


   S $ Header text:

When a file is saved, an embedded header is also saved.  this contains file size information and a text
string or header text.  Use this option to view the current header text, or to write new header text. 
   T F( In the Renew header text option type the text, up to a maximum of 503 characters, and exit by
   T ) typing <CONTROL>ĩZ.  Alternatively, <ESCAPE> quits the option.  Any header text is loaded  and   )
       p-@*@*@@  saved with the image.

   T  A note about header information:  Those who have used BILKO 1.1 should note that BILKO 1.3
differs from it by handling data files which contain header information embedded at the beginning of
the .DAT file.  There is therefore no .HDR file required with BILKO 1.3 .DAT files.   However,
BILKO 1.1 .DAT files may still be loaded directly into BILKO 1.3 provided there is a corresponding
   T  .HDR file in the same directory.  Any .DAT files created by the Save image function in BILKO 1.3
have the embedded header information automatically generated.  For images no larger than 512 pixels
x 256 lines this provides a satisfactory method of converting BILKO 1.1 files to BILKO 1.3 formats. 
Simply load into BILKO the 1.1 file and then save it under a new name.  Any additional text that was
   T r in the .HDR file is lost, but new header text may be input via the Renew header text option (see
above).  There is no change in the .STR and .PAL file formats between versions 1.1 and 1.3. 
   T #
 Further information about preparing images for use with BILKO is given in Section 3: A lesson for
   R 
 lesson creators.

   T  The Add constant option allows the user to add an integer value to an image file.  The resultant
image is saved to disk under a separate file name.  The original image must be in a file with the new
format.

   T  The Convert option is included to convert BILKO 1.1 format files (with associated .hdr files) into
BILKO 1.2 and BILKO 1.3 new format files in which the header information is embedded in the
image file itself


   S G 13. Filters

   T  The Filters menu allows the user to apply a filtering process to an image.  The first two options
   T  operate on the currently loaded image.  In the case of the Smooth and Gradient functions, the
   T  original image is lost from memory to be replaced by the smoothed or gradients image.  The Smooth
   T  and Gradient options act as low and high pass filters respectively as the names suggest.  The
   T [ Gradient filter evaluates the difference between the diagonally opposite corners of a 2 ' 2 group of
pixels, and sums their absolute values.

   T  Activity:  `	`	 Apply the Gradient option to EIRE4.DAT.  Select the Modify LUT option and
   T  perform a contrast stretch with Histogram equalization. The boundary between land
and water areas is sharpened, as are the gradients within the water area itself.  Note,
for example, the thermal gradients associated with the front lying off the North East
Coast of Northern Ireland."`	

   T    X  X`	`	 Return to the Main Menu and select the Histogram option. Notice how selection of
   T ! the Gradient option has modified the original bimodal pattern of the histogram."`	

   T # Question 4:  `	`	 Reload the original EIRE4.DAT and before running Gradients on it, apply the
   T Y$ Smooth option first.  What is the effect of applying Smooth first?"`	


The remaining three filter options on the menu operate on an image file on disk and write the new
file to disk.  The input image has to be named and the output (filtered) image is given a default name. 
Note that if the same filter option is applied to several images, the default file will be overwritten.    (        p-@*@*@@  To preserve a filtered image under these circumstances, it must be renamed.  This can be done either
by loading it with its default name and then saving it with a new name, or by using the MSDOS
   T  REName command which can be reached through the DOS shell option under Miscellaneous.

   T a The Texture filter replaces each pixel value by the variance of the group of 3'3 pixels of which it
is the centre.  The filtered image is given the name TEXTURE.DAT

   T  The Median filter replaces each pixel value by the median of the group of 3'3 pixels of which it
is the centre.  The filtered image is give the name MEDIAN.DAT

   T s The 3'3 filter is a general filter in which the weights (integers) are defined by the user.  The filter
operates over the input image in the usual way.  The filtered image is given the name 3X3.DAT


   S  14. Printing images

Although no direct printing is supported in BILKO 1.3, any graphics printer with a PRINT SCREEN
driver may be initialised before entering BILKO 1.3 to enable screen dumps to the printer.  Please
note that the BILKO 1.3 images are displayed on the second graphics page (except for the VGA256
option which is on the first page) and the driver should be set accordingly.  The same applies to
   T  software which grabs image files for import into display or graphics software packages.  Hint: if you
cannot set your screen grab software to access the second page, it is still possible to grab an image
   T  by using the Toggle function.  The second image to be loaded is stored in the first page and can thus
be readily captured.





      y    b                     d       d d                                                                         y 

The BILKO software was written by R.D.Callison.  This Introductory Tutorial was written by
R.D.Callison and D.A.Blackburn.


   R  Comments or suggestions relating to this lesson should be sent to:

   R w Dr.R.D.Callison  hh# ( - Fax:pp2 (44) 382 561590)
Pharos Scientific Ltd.
Unit #9, Prospect Business Centre and Technology Park
   R   Dundee, DD2 1TY, United Kingdom






   &         p-@*@*@@     T    Aa Answers to Questions - Section 1ă


Question 1

1.1        34
1.2      3668

Question 2

Detail can be seen in land areas but very little remains in sea areas.

Question 3

You should now see clearly that the warmer waters are shown in red shades, while colder waters are
shown in blue shades, and the land has been masked out.

(Note that it may be necessary to adjust the contrast and brightness controls on your monitor in order
that the various shades of colour are clearly distinguishable from one another).

Question 4

There is a loss of detail.
