Technology ICT Option: Gimp

1. Technology • ICT • Option: Gimp

2. 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

3. 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

4. Digital Imaging - Gimp • Colour models • Image editing software uses colour models to represent the production of colour on the screen and on paper. The main models in use are: • 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

5. 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

6. Digital Imaging - Gimp • Graphics formats • Digital images come in two main types: • 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

7. 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

8. Digital Imaging - Gimp • Digital file formats • 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) • 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 it’s 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

9. 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 logo’s, 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

10. Digital Imaging - Gimp • The most common proprietary file formats are: • 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 • 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

11. 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: • http://gimp.org/windows/ • Installing the GNU IMP is a three stage process: • The Runtime Environment must be installed first • The Program files are installed next • The Help System (optional) files are installed last

12. 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 it’s options are shown Dialogs (Palettes in Photoshop) such as Layers, Brushes, Histogram etc. also appear in separate windows

13. 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

14. 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: • 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 don’t belong in any other category Selection tools Transform tools Paint tools

15. 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

16. 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

17. 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

18. 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

19. 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)

20. 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 • To open an image file from the editor: • 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

21. 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

22. Digital Imaging - Gimp • To do a preview scan: • Click the preview button. When the scan is finished, the right hand portion of the scan window will display the preview

23. 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

24. 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

25. 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. • When the camera is connected to the computer, it is seen as a removable disk drive and the Removable Disk window opens: • Select Copy Pictures to a folder and click OK

26. Digital Imaging - Gimp • The Scanner and camera wizard opens. Click Next • Tick the required images or choose Select All

27. 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

28. 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

29. 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

30. 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

31. 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