GIMP Class
This class will give you the skills to open, edit and combine images using the powerful program named GIMP.
This wiki page can be found at http://bit.ly/gimpclass
To Install
GIMP will likely be installed on your computer already, but if not, you can find it in Synaptic Package Manager under "gimp." Once selected, choose "yes" to install the needed dependencies as well. Other useful packages are "gimp-data-extras," which includes extra brushes and gradients, and the "gimp-help-en" package which is the help manual.
Three ways to start GIMP
Once installed, start GIMP from the "Applications - Graphics" menu.
or run the command "gimp."
or right-click on the image you want to edit, and choose "Open With..." then "GNU Image Manipulation Program."
Alternate Ways to Open an Image File
Drag the picture file from the Desktop or File Browser into the toolbox.
- alternately -
Choose the File menu, then "Open..." then browse to the file you wish to open.
Windows of GIMP
Your image will appear in the Image window. Across the top of the window you will find the filename, what kind of image it is, (RGB Color or Greyscale etc) how many layers it has, and the image's pixel dimensions as width times height.
Each image window has its own menu directly under the first part. If you have multiple images open, it is helpful each window has its own menu to help from accidentally editing the wrong image's settings.
The rulers on the edges of the picture both help measure the space and function as guides. Click and drag a ruler onto the image and it will form a blue guide line. Guide lines will not show up when the image is printed but will help you arrange elements of your image.
Later on, when you are moving selections and layers around, you will find the "snap to" feature that is on by default on the guides makes it very easy to line things up.
If you want your rulers to display another unit of measurement, you can choose from the drop-down menu at the left on the bottom of the image window. Right now it should say "px." You can choose centimeters, picas, inches and more.
To the right of the unit of measurement selection is the quick-zoom menu, followed lastly by the name of the active Layer and how much temporary memory the image is using in parenthesis. The tiny icons in the corners are fun, the top right locks in the current image ratio, so when you resize the window it automatically zooms the image. If you are working close up and want to move to another close up part of the image, click and hold the navigation icon on the bottom right (same icon as the Move icon) until you get to the part of the image you want to be at.
The tall skinny window on the left, labeled "Toolbar" on the top, is where you will choose the image manipulation tool you want to use, and control the settings of the tool. The other skinny tall window are more tool options and ways to select and isolate different aspects of the image. But we'll get to that later! The remaining central window is the image window.
The tools in the toolbox are represented as icons. Hover over a tool and a tip will pop up telling you the name of the tool and the keyboard shortcut (if it has one).
If you would prefer a menu, the "Tools" menu in the image window has them grouped into general type.
For more info, see Toolbox section below.
So that's a quick intro to the image window! Let's move on to your first image manipulation!
The default tool is usually the Paintbrush. If you click and drag on the image with that tool selected, you will paint on the active layer, and an *asterisk will appear before the filename warning you that the changes to the image have not been saved. But you likely don't want an ugly black stripe on your image, so that leads us too:
GIMP undo-history
Everything you do can be fixed
GIMP makes a mistake as easy to fix as the keyboard shortcut "ctrl-z." The motto is: Try it and undo the paint brush stroke.
The only time you cannot undo is the human motion between certain processes, when the mouse is clicked for the paintbrush or free-select tool until it is released. You can undo the whole mouse-stroke, but you cannot go back to specific portions of the stroke. That is why they invented Paths, which is in GIMP 2 and awesome.
GIMP keeps extensive undo history, which can be a toolbar tab or a separate floating window. And if you "undid" but you wish you didn't, the "Redo" command will restore you back to before the undo.
Once you have saved and exited the program, however, you lose the chance to undo. So only close GIMP when you know you are done with the image!
Selections
GIMP allows you to edit parts of an image separately from the rest of the image. To do this, you must designate the area you want to manipulate with a "selection."
There are many ways to make a selection. You can simply draw a square, elliptical or free-hand shape around an object or you can select by color in a number of ways. The tools are explained in the Toolbox section below. The concept is important: once an area is selected, any changes you make to the image will only change the selection. You can change the color, paint on it, even delete it, all without affecting the remaining image outside of the selection.
Once you have made your selection, it will have trailing black lines around it to symbolize it is a selection.
Layers as Permanent Selections
If you have made a selection that you wish to make more permanent, Copy it to the clipboard with "Ctrl-C," then Paste with "Ctrl-V" which will paste a copy of the selection onto the image. Then pull down the Layer menu and choose "New Layer..."
Ta-da! You have a new layer consisting of your selection that is stacked on top of your existing image. You can edit, move and alter this layer to your heart's content, and if you save your image as a GIMP image, when you open it up at a later time, all of your layers will remain.
This is important because you can only work with one selection at a time, but can have as many layers as you want. More on layers below...
The Toolbox
Now that we've got those concepts seeded, let's introduce the Toolbox. It's the box with all the little icons in the skinny window labeled Toolbox.
Each icon offers a quick way to select different tools for manipulating images. At any time you can hover over an icon and it will tell you what it is named. For beginners, while working at home, it may be useful to keep a tab open with GIMP's manual for quick reference: http://www.gimp.org/docs/ Choose your language, and "Ctrl-F" in your browser should let you search for the tool's name.
In class, I start with the top-left tool in the toolbar, the dotted-line square. This is the basic selection tool. It is used to draw a box around and capture a specific square portion of an image. To use the tool, select the tool in the toolbox by left clicking on it, move the mouse icon to the image, then left click and drag the box around the portion of the image that you want to capture. Once the box is created you can move the edges to fine-tune your selection by clicking and dragging on the corners of the box. Click once on an edge and use the direction keys, for finer control.
The entire top row of tools are basically derivations of the selection tool. The next two tools are for selecting elliptical objects and draw a free-hand selection around something (very difficult).
The magic wand is a great tool, Fuzzy Select, which will deduce objects and select them by matching colors. Works great with high-contrast photos. Click a bright green lawn in a photo and the lawn will be selected. Click a red dress and the dress will be selected but not the other reds in the photo.
The next tool, Select by Color WILL select by color regardless if they are apart from each other.
The scissor icon uses "intelligent edge-fitting" to select objects from images along computer-assisted edges.
Saving a couple for GIMP 2, we'll skip to the eyedropper tool, the color selector. Very useful. Use it to find colors you like in your photos and set it as your Foreground or Background color, for use in filters, text or painting.
The next tool is the zoom tool, looks like a magnifying glass. Click on the image to zoom, ctrl-click to zoom out, or draw a box around where you want to zoom. I personally prefer the keyboard shortcuts "+" and "-" on the Num Pad to zoom in and out.
The measurement tool, a compass, is a helpful way to measure objects, layers or selections in your images. Certain ratios are naturally more appealing to the eye...
Moving on, you can move layers and selections using the Move tool. It is the two blue crossed arrows. You will use this tool a lot and I think it should be the default tool.
We'll skip the alignment tool, going on to Crop, the logo of a precision knife. This tool is an easy way to trim down an image. Draw a box, resize it by dragging the corners, and when you're satisfied, click in the middle to crop to the box. Especially useful after you've used Rotate, the next tool, to straighten a crooked snapshot.
The Rotate tool, a square rotating, allows you to rotate the image, layer, selection or path.
The next four tools work much the same way. The Scale tool is used to resize the image, layer or selection.
Shear tool "tilts" the image or selection.
Perspective is a fun tool to change the perspective of the image or selection.
Flip simply reverses the image or selection, horizontally or vertically.
The two overlapping squares, below the icons, are the foreground and background colors. It starts with black as the default foreground and white as the default background, so that if you paint it will be black and if you erase it will reveal white.
We'll hold off on the rest of the tools until GIMP 2 in order to explain the extremely vital resource that allows you to control each tool's option, found below the toolbox: the toolbar.
The Toolbar
The Tool Options and so much more
The toolbar can have many tabs. We will only cover the main tab, the Tool Properties tab here. The icon looks like a tiny mixer board.
When a tool in the toolbox is selected, that tool's options will be displayed in the Tool Properties. Each tool will perform a function without changing any options, but most options will dramatically change the properties of the tool. Experiment with the options! You can always undo!
The small arrow to the right of the Tool Properties title will allow you to add tabs to your toolbar.
For this example, choose Add Tab>Layers to add the Layers tab to the toolbar.
Layers
With layers, you can apply effects to specific parts of the image while leaving the rest unchanged.
Select which layer you are working with by left-clicking on it in the Layers toolbar. Be aware of which layer is selected when you are making your edits! The active layer will have a black and yellow striped border.
The default name for the base layer is "Background." You can rename any layer by double-clicking on the name in the Layer toolbox. Type the label you wish and hit "enter" to complete.
Creating a New Layer
If you want to add a new image as a new layer, simply drag and drop it into your image window. You will see it appear as its own layer in the Layer toolbar.
For a new blank layer, choose Layer>New Layer from the image menu, which will pop up a dialog giving you an option to name the layer and adjust its properties. Name the layer whatever you want and ensure it will be a Transparent layer. Finish by clicking OK when done. Draw on your new layer without affecting your original image!
The text tool automatically creates a new layer for the text, but more on that in GIMP 2 :)
Working with Layers
You can paste an image from the clipboard with "Ctrl-V", which can come from any other image or program like a web browser. The pasted image will appear as a floating selection (with trailing lines around it) until you anchor it onto the next layer down with the anchor button in the Layer toolbox. If you want the floating selection to become its own layer click the new layer button.
If you want to see "under" the layer momentarily, you can make the layer invisible by clicking on the Eye icon in the Layer toolbar. Click the empty box to make the layer visible again.
If you wish to see "through" the layer permanently, on the Layer property, select the layer and adjust the Opacity slider. This enables you to blend images together.
Saving files
Save files by selecting File>Save on the image menu. Choose a filename and file format, i.e. "image.jpg"
You can type the location into the filename bar if you so desire, i.e. "~/Images/image.png" which would save it in my home folder/Images as image.png
You can also browse to the folder where you want to save the file and just type the filename.
File Formats
GIMP will open practically any image file and can save in the same number of formats.
Especially if you are saving an image with more than one layer, save your images in GIMP image format, ".xcf" This will allow you to open the image later and retain the separate layer information.
Unfortunately, GIMP-format images will not display on the web, so if you want to share it, you need to save in a common file format.
Commonly used file types used on the internet are PNG and JPEG, represented by ".png" and ".jpg"
Web images require the layers in the image to be flattened, which GIMP will warn you as you save, meaning when you open it again you will only have one layer.
Colorize
One of the many effects under the menu item Colors is Colorize.
This is an easy way to change the hue, saturation and lightness with one tool.
Freeki Filters
Because we are working with Layers, we can add effects to the Background and "upper" Layer separately. Try it out! Extract a piece of an image, make it a new layer and turn it into a cartoon, ripple and warp it, add sun flares or supernovas....there are tons of fun Filters that are added to constantly.
Don't forget, it is easy to undo anything, so go ahead and try things out. In class, we will go over a few of my favorite filters if we have enough time.
Hopefully, these skills will give you the confidence and footing to begin to explore the possibilities that GIMP can offer you! Good luck!
Jackson