OVERVIEW: learning the basics of digital image manipulation using GIMP

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1 OVERVIEW: learning the basics of digital image manipulation using GIMP This learning resource contains information about a small part of GIMP. Extensive documentation can be found online: Most of the information below was gathered from this website. What is GIMP? GIMP is a multi-platform photo manipulation tool. GIMP is an acronym for GNU Image Manipulation Program. The GIMP is suitable for a variety of image manipulation tasks, including photo retouching, image composition, and image construction. Basic concepts: IMAGES Images are the basic entities used by GIMP. Roughly speaking, an image corresponds to a single file. A GIMP image may be quite a complicated thing. Instead of thinking of it as something like a sheet of paper with a picture on it, think of it as more like a book, whose pages are called layers. LAYERS If an image is like a book, then a layer is like a page within the book. The simplest images contain only a single layer, and can be treated like single sheets of paper. Sophisticated GIMP users often deal with images containing many layers, even dozens of them. FORMAT Image files can have different formats (JPEG, TIFF, PNG, etc.). Each format uses a specific type of compression. Depending on the use we are going to give to our image we may use one file format or another. For example TIFF is a format that allows for very good quality images and therefore it is used for large-scale image printing. JPEG allows bigger compression and it is used when less quality is needed. for more resources visit page 1of5

2 MAIN WINDOWS The screenshot above shows the most basic arrangement of GIMP windows that can be used effectively. 1. The Main Toolbox: Contains a set of icon buttons used to select tools. May also contain the foreground and background colors; brush, pattern, and Gradient; and an icon of the active image. Use Edit Preferences Toolbox to enable, or disable the extra items. 2. Tool options: Docked below the main Toolbox is a Tool Options dialog, showing options for the currently selected tool (in this case, the Smudge tool). 3. An image window: Each image open in GIMP is displayed in a separate window. Many images can be open at the same time, limited by only the system resources. Before you can do anything useful in GIMP, you need to have at least one image window open. The image window holds the Menu of the main commands of GIMP (File, Edit, Select...), which you can also get by right-clicking on the window. 4. The Layers, Channels, Paths dock with the Layers Dialog open; note that the dialogs in the dock are tabs. This dialog window shows the layer structure of the currently active image, and allows it to be manipulated in a variety of ways. It is possible to do a few very basic things without using the Layers dialog, but even moderately sophisticated GIMP users find it indispensable to have the Layers dialog available at all times. for more resources visit page 2of5

3 5. Brushes/Patterns/Gradients: The docked dialog below the layer dialog shows the dialogs (tabs) for managing brushes, patterns and gradients. Basic operations we are going to use today CROP 1. Click the button in the Toolbox. 2. Click and drag. 3. Adjust by placing the mouse inside the rectangle you ve created in the previous step and clicking and dragging again. 4. Double click inside the selection to crop. SELECT Often when you operate on an image, you only want part of it to be affected. In GIMP, you make this happen by selecting that part. Most, but not all, GIMP operations act only on the selected portions of the image. ( For this exercise open two different images. - Rectangular and elliptical selection 1. Click the button in the toolbox. for more resources visit page 3of5

4 2. Click and drag on image Right-Click > edit > copy. 4. Open image 2. Right-click > edit > paste. - Lasso The Free Selection tool, or Lasso, lets you create a selection by drawing it free-hand with the pointer, while holding down the left mouse button. - The poligonal selection (Only with GIMP-2.6) Instead of click-and-dragging to draw a free hand selection, you can click only. This creates an anchor point. Then moving the mouse pointer draws a line with a new anchor point that you can move as long as you don't click again (the mouse pointer comes with the moving cross). for more resources visit page 4of5

5 CHANGE IMAGE SIZE When you have a huge image and you want to resize it so that it displays nicely on a web page, do the following: 1. Open the scale image dialog. IMAGE > SCALE IMAGE. 2. Give the new measures ALWAYS keeping the proportions. 3. Click OK. CHANGE BRIGHTNESS & CONTRAST The Brightness-Contrast tool adjusts the brightness and contrast levels for the active layer or selection. This tool is easy to use, but relatively unsophisticated. 1. Open TOOLS > COLOUR TOOLS > BRIGHTNESS-CONTRAST 2. The brightness slider sets a negative (to darken) or positive (to brighten) value for the brightness, decreasing or increasing bright tones. 3. The contrast slider sets a negative (to decrease) or positive (to increase) value for the contrast. Conclusion: This quick introduction to GIMP will allow us to create collages of images gathered from the Internet. These compositions can then be used to customise the desktop of the laptops or to create online avatars. for more resources visit page 5of5