Technology

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• Technology
• ICT
• Option Gimp

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Digital Imaging - Gimp
A digital image is a computer representation of a
photograph It is composed of a grid of tiny
squares called pixels (picture elements) Each
pixel has a position on the grid and a colour
value These pixels can be edited (changing the
pixel colours) individually on in groups   The
illustration below shows an image of a car and a
section of it zoomed to show the individual
pixels The shape of the pixels is clear as is
their positions on the grid making up the digital
photograph
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Digital Imaging - Gimp
The resolution of an image is the number of
pixels it contains This is normally given as dots
(pixels) per inch (dpi) or dots per centimetre
(dpcm) The resolution of an image effects its
quality - higher resolution - better quality,
but this comes at a price as an increase in
resolution means an increase in file size A
doubling of the resolution produces a quadrupling
of the file size The chart below shows
photographs taken at 150dpi and 300dpi The
resultant file sizes are shown when the
photograph is taken as black and white, grayscale
and colour
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Digital Imaging - Gimp

• Colour models
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• Image editing software uses colour models to
  represent the production of colour on the screen
  and on paper. The main models in use are
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• The RGB Model - used on computer monitors and
  projectors. Values ranging from 0 to 255 can be
  assigned to each of the primary colours red,
  green and blue. These colours are known as the
  additive primaries because if they are combined
  at full value (255), they produce white. If they
  are combined at values of 0, the resulting colour
  is black. All other colours are achieved by
  varying the values assigned to the three primaries

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Digital Imaging - Gimp

• The CMYK model - used for printing. Based on
  the colours cyan, magenta and yellow. In
  theory, pure cyan (C), magenta (M), and yellow
  (Y) pigments should combine to produce black.
  For this reason these colours are called
  subtractive colours. Because all printing inks
  contain impurities, these three inks actually
  produce a dark brown and must be combined with
  black (K - Keystone black) ink to produce a
  true black . As it uses percentages for each
  colour, the values only go to 100 and not 255 as
  in RGB
• The subtractive (CMY) and additive (RGB) colours
  are complementary colours. Each pair of
  subtractive colours creates an additive colour,
  and vice versa

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Digital Imaging - Gimp

• Graphics formats
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• Digital images come in two main types
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• Bitmap images - made up of a grid of pixels.
  Similar to a mosaic, each pixel has an address
  and a colour value. As the number of pixels is
  fixed (resolution dependant), these images become
  jagged when enlarged. Photographs are held as
  bitmaps because they can display the vast number
  of colours necessary for photo realism. Paint
  software produces bitmap graphics

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Digital Imaging - Gimp

• Vector images - a series of geometric objects
  such as lines and curves. Each object will have
  properties such as colour, width, size, fill and
  position. They are resolution independent and
  can be scaled without any loss of resolution.
  Photo realism is difficult to achieve with vector
  graphics and because of this they are rarely used
  for photographs. They tend to be used in logo
  creation and technical drawings. Their file
  sizes are considerably smaller than bitmap image
  files

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Digital Imaging - Gimp

• Digital file formats
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• Image editing software can open and save files in
  many file formats Some of the file formats are
  universal and can be produced by any image
  editing program
• Others are proprietary which means they are
  produced by specific image editing programs
  (Photoshop, GIMP etc)
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• The most common universal file formats are
• BMP - this is the Microsoft graphics format.
  Images produced using MS Paint will be BMP
• TIFF - these are high quality images. A good
  digital camera will offer TIFF as its best
  output. It produces images with a large file size
  and is used in magazines etc
• JPEG - This is the most common file type
  created by digital cameras. JPEG images use lossy
  compression. This means that quality of the image
  is reduces to give a smaller file size

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Digital Imaging - Gimp

• GIF - Gif (graphics Interchange Format) files
  can only display 256 colours in an image compared
  to 16 million in a TIFF image. Because of this,
  it is used mainly for logos, drawings and
  diagrams. GIF images can have transparency and
  this is useful when placing an image on a
  coloured background
• PNG - This file format (Portable Network
  Graphic) was designed as a replacement for GIF.
  It has the transparency advantage of GIF and can
  hold a lot more colours making it suitable for
  photographs

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Digital Imaging - Gimp

• The most common proprietary file formats are
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• PSD - these files are produced in Photoshop
• PSP - these files are produced in Paint Shop
  Pro
• XCF - these files are produced in GIMP
• CPT - these files are produced in Corel Photo
  Paint
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• As these file types are proprietary, they will
  have special features not available in universal
  file types
• For this reason they can usually only be opened
  in their own programs
• They must be converted into a universal file
  format to be used in wordprocessing etc

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Digital Imaging - Gimp

• The GNU IMP (GIMP - GNU Image Manipulation
  Program) is a totally free image editing program
  and has most of the features of expensive
  programs like Photoshop etc 
• It can be downloaded as three separate files
  from
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• http//gimp.org/windows/
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• Installing the GNU IMP is a three stage process
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• The Runtime Environment must be installed first
• The Program files are installed next
• The Help System (optional) files are installed
  last

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Digital Imaging - Gimp
The GIMP interface is very different from other
image editing programs in that it doesn't present
a single window as an interface. When the Gimp
is opened, only the Toolbox and its options are
shown   Dialogs (Palettes in Photoshop) such as
Layers, Brushes, Histogram etc. also appear in
separate windows
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Digital Imaging - Gimp
When an image in opened in GIMP, it opens as a
new window The floating windows can be dragged
to anywhere on the screen. The image below shows
them arranged as in most image editing programs.
This arrangement is saved automatically and will
be in place when the program is next opened
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Digital Imaging - Gimp

• The full range of tools are available from the
  drop down menus , but the most common tools are
  found in the Toolbox. The tools can be broken
  into five main categories
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• Selection tools - are used to select an area of
  an image for editing.
• Paint tools - used to change colours in an
  image or area of an image
• Transform tools - used to rotate, flip, scale
  etc. images.
• Colour tools - change the distribution of
  colours in the image.
• Other tools - tools that dont belong in any
  other category

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Digital Imaging - Gimp
Each of the tools in the GIMP has its own set of
options These appear below the toolbox when a
tool is selected. Below are all the options
available when the Rectangular Selection tool is
selected and when the Fill tool is selected
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Digital Imaging - Gimp

• Dialogs help with the editing process
• They are accessed from the File menu. The main
  ones are shown below
• Histogram - shows the spread of pixels in the
  image (Levels)
• The pixels will be divided between the
  Highlights on the right of the graph and the
  Shadows on the left and the Gamma (mid-tones) in
  the centre of the graph.
• A perfect image will show as a bell curve
• This example needs correction as it is
  overexposed - not enough pixels in the shadows
  area
• An underexposed image has insufficient pixels in
  the highlights area

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Digital Imaging - Gimp

• Undo History dialog keeps a record of all the
  editing processes carried out on the image
• Clicking the Base Image icon undoes the entire
  editing session
• Selecting any of the edits and clicking the
  Undo button at the bottom of the dialog undoes
  that edit
• The huge advantage of this is this system is
  that you can undo any past edit at any time
• Normal undo has to be done in the reverse order
  to the edits

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Digital Imaging - Gimp

• Brushes - used to select a brush for use with
  the painting tools
• Hard edged or Soft edged brushes are available
  in different sizes and shapes
• Navigator - controls image magnification and
  the viewing area
• Dragging the slider at the bottom zooms the
  image in and out
• Dragging the box around the dialog controls the
  area of the image shown in the workspace
• Clicking an area of the image within the dialog
  moves the rectangle to that area
• The buttons at the bottom of the dialog offer
  set magnifications

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Digital Imaging - Gimp

• Images - shows thumbnails of all the open
  images
• If the images are stacked in the image area, the
  images dialog can be used to control which image
  is currently showing
• Simply select the required image and click the
  Display button or double-click the thumbnail of
  the image
• Layers - shows all the layers in the image in
  stacking order
• Images or paint can be placed on individual
  sheets and edited without effecting images on
  other sheets
• Layers can be dragged up or down the stack and
  display is controlled by toggling the eye icon to
  the left of each layer
• To edit a layer it must be active (highlighted)

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Digital Imaging - Gimp

• Opening images - files in all the universal
  formats can be opened in the workspace. Depending
  on the amount of memory in the computer, several
  images can be open in the editor at the same time
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• To open an image file from the editor
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• Click the File menu and choose Open. The Open
  Image dialog box opens.
• Navigate to the folder containing the file
• Click the file to select it and click the Open
  button

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Digital Imaging - Gimp
Inputting Images Scanning digitises an image so
that it can be read, displayed, edited and
printed by a computer.   To scan an image in
GIMP   Click the File menu and choose Acquire,
then Twain and select the scanner Scanning
takes place in two stages - preview and then
final scan. The preview scan allows you to
select the exact area of the page or photograph
you want to scan
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Digital Imaging - Gimp

• To do a preview scan
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• Click the preview button. When the scan is
  finished, the right hand portion of the scan
  window will display the preview

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Digital Imaging - Gimp
Before performing the final scan, the software
needs to know some information Firstly, the
exact area of the image to be scanned needs to be
set. This is done by dragging the handles in the
preview window Secondly, the image type must be
set. This can be colour, grayscale, black and
white or custom settings When all the settings
are set, Click Scan. The image is scanned into
Gimp and is ready for editing
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Digital Imaging - Gimp
What resolution to use   The simple formula
below can be used to set the scanning
resolution         Example - An original
photograph is 50mm x 50mm. It is to be printed
at 300dpi. The photograph is to be scaled to
100mm x 100mm in the publication. What
resolution should the scanner be set to Using
the above formula           Answer (300/50) x
100 600dpi
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Digital Imaging - Gimp

• A Digital Camera stores pictures electronically
  on a small internal memory card. The pictures
  can then be transferred from the card to the
  computer.
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• When the camera is connected to the computer, it
  is seen as a removable disk drive and the
  Removable Disk window opens
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• Select Copy Pictures to a folder and click OK

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Digital Imaging - Gimp

• The Scanner and camera wizard opens. Click Next
• Tick the required images or choose Select All

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Digital Imaging - Gimp

• Choose a folder for the images. Tick the Delete
  Pictures box if you want the pictures erased from
  the memory card
• The images are copied to the folder
• Click Next in the following screen and Finish

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Digital Imaging - Gimp
Alternatively, you can choose Open folder to view
files in the Removable Disk window to control the
files as if they were of a disk drive
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Digital Imaging - Gimp

• Selecting - Just as text to be edited in a
  word-processor must be selected, an area of an
  image or an entire image must be selected if it
  is to be edited
• The main selection tools are
• Area Selection Tool - The rectangular and
  elliptical tools select a defined shape. Select
  the tool and drag the required area. The area is
  surrounded by marching ants. Hold down the Shift
  key while dragging to constrain the shape to a
  perfect square or circle

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Digital Imaging - Gimp

• Free Selection Tool - Use this tool to drag
  freehand selections. Select the tool and drag
  the freehand shape. Releasing the mouse joins
  the start and end points. A difficult tool to
  control for precise selections
• Fuzzy Selection Tool - Most image editing
  programs call this tool the magic wand tool. It
  selects areas based on colour. Choose the tool
  and pick a pixel. Set the threshold in the
  options. This is the variation in shade that will
  be included in the selection

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Digital Imaging - Gimp

• Intelligent Scissors Tool - selects highly
  contrasting edges by allowing the positioning of
  control nodes around the edges of the image.
  Click around the edges and join the last point to
  the first. Click anywhere inside the perimeter
  to complete the selection
• Path Tool - used to create selections. Edit
  Mode in the Options area must be set to Design.
  The tool creates nodes as above, but there is no
  intelligent edge finding. A curve is generated
  between the nodes to create a perimeter. When
  the perimeter is complete - by CTRL Clicking
  the start point - click the Create Selection
  From Path button