GIMP Class

This class will give you the skills to open, edit and combine images using the powerful program named GIMP.

To Install

GIMP will likely be installed on your computer already, but if not, you can find it in Synaptic Package Manager under "gimp." Other useful packages are "gimp-data-extras" that include extra brushes and gradients, and the "gimp-help-en" package.

Different Ways to Open a File

Right-click on the file and choose "Open with...GIMP Image Editor."

or

If GIMP is running, drag the picture file into the toolbar.

Once a file has been opened, it will appear in a list under "Open Recent" in the File menu, so you can find your recent work easily.

Intro to GIMP 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, you can undo ;)

The only time you cannot undo is the human motion during certain processes, like the paintbrush or free-select tool. You can undo the whole mouse-stroke, once the button is released, but you cannot go back to specific portions of the stroke.

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. You can even undo an undo.

The Toolbox

The box with all the little icons is the toolbox. Each icon offers a quick way to select different tools for manipulating images. The two overlapping squares below the icons are the foreground and background colors.

We'll start with the top-left tool in the toolbar, the dotted-line square. This is the basic selection tool. It can be used to draw a box around and capture a specific 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, or clicking on the edge and using the direction keys for more control.

Once you have made your selection, it will have trailing lines around it, and you will be able to copy it to the clipboard with "Ctrl-C" to use in another image or to make into a new layer. You may also manipulate the selection like its own layer, but you can only work with one selection at a time, where you can work with as many layers as you want, so it's a good idea to use layers. More on layers below...

The entire top row of tools are basically derivations of the selection tool. The next three tools are: select elliptical objects, draw a free-hand selection around something (very difficult), and do a fuzzy select which will deduce objects and select them by matching colors.

The next tool selects by color, selecting regions that match even if they are apart from each other.

The scissor icon uses "intelligent edge-fitting" to select objects from images.

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 to use for 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.

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.

We'll hold off on the rest of the tools until GIMP 2 in order to explain the 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 you select a tool in the toolbox, 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 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 that will let you push "Ctrl-C" or copy to the clipboard. 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 easily "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.

Colourize

One of the many effects under the menu item Colours is Colourize.

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