The GIMP is a powerful, free, open source image manipulation program. It is available for download at http://www.gimp.org/. It has an easily understood online user manual, which may be accessed at http://docs.gimp.org/en/. These notes are intended as a translation tool to allow users of the GIMP to follow the steps in Tim’s tutorials. Tim’s explanations are excellent, so I have no intention of rewriting them. Often I will provide links to specific sections of the online manual as well. The tools of the GIMP are not always an exact counterpart to those of Photoshop, and not all of the work in the tutorials can be easily done in the GIMP. However, it is the hope that these notes will be of use.
Basics of the GIMP
When the GIMP is opened, there are typically three windows, an image window, a toolbox, and a dock of dialogs. While the multiple window format may seem strange at first, the arrangement has its advantages. Hitting the Tab key will hide the toolbox and dock, so one can use the whole screen to work on the image. A second tap of the Tab key will restore these items.
The toolbox has all the tools that are used to edit an image. Hovering over a tool’s icon will reveal a tool tip that explains its function and gives a keyboard shortcut. Memorizing the keyboard shortcuts of frequently used tools is a great time saver. When a tool is selected, the bottom half of the toolbox displays its properties, which can then be modified.
The dock contains a couple of important dialogs that have been fused together into one window. As a user, you can customize this dock to fit your needs. More help is available at http://docs.gimp.org/en/gimp-concepts-docks.html.
Notes for Tutorial One
Copying an image from the tutorial to the GIMP
Right click the image in the tutorial and select Copy. Go to the GIMP. From the File Menu, select Create, From Clipboard.
The Eyedropper Tool
As in Photoshop, this looks like an eyedropper; keyboard shortcut O. The instructions are the same as in the tutorial. More information on this tool is at http://docs.gimp.org/en/gimp-tool-color-picker.html.
The Paintbrush Tool
This looks very much like the corresponding tool in Photoshop; keyboard shortcut P. When the tool is selected, its attributes are in the lower half of the Toolbox window. The brush sizes in the GIMP do not match those of Photoshop; you will need to experiment on your own. Perhaps I was impatient, but I also found that the opacity of 15% was inadequate in the GIMP. I got good results at 50%. More information on the Paintbrush tool is at http://docs.gimp.org/en/gimp-tool-paintbrush.html.
The Burn Tool
This looks like a lollypop, keyboard shortcut Shift + D. Dodge and burn are together, you have to use the properties dialog to select the one you want. (In Photoshop, the dodge tool appears as a lollypop, and the burn tool like a hand in the shape of an O. The GIMP combines both tools and so uses one symbol.) You can select the brush size and opacity. I used opacity of 34% to do the work in the tutorial. The dodge and burn tools are described at http://docs.gimp.org/en/gimp-tool-dodge-burn.html.
Notes for Tutorial Two
The Clone Tool
Just as in Photoshop, the clone tool looks like a rubber stamp. Select it by clicking its icon or typing its keyboard shortcut C. The properties box allows selection of the type and size of brush, opacity and other items. To activate the clone tool, place the mouse pointer at the point that contains the good information that you want to copy. Hold down Control, left click, and the tool is activated. You can then move the mouse pointer to the area to be repaired. You will see two circles, one with crosshairs indicating the good area of the image, and one with no cross hairs. You will want to place this at the edge of the area to be repaired. Press and hold down the mouse pointer; as you move the mouse, both circles move together and the good area replaces the bad. Mistakes are inevitable. As in Photoshop, Ctrl + Z will erase the last action. Unlike Photoshop, using Ctrl + Z again is sufficient to erase the action two or more steps back. Reducing the opacity below 100% is useful if there are slight variations in color between the damaged area and the good area. More information on this tool is found at http://docs.gimp.org/en/gimp-tool-clone.html.
Notes for Tutorial Three
As you can tell from tutorial three, the ability to select a part of an image and work on it is an essential skill for editing photos. Since this is so important, I thought I would go over all the tools used to select a part of an image. The GIMP has seven selection tools, a Path tool that can be used to create selections, and other techniques for modifying selections. If you just want to see how to select the flower in tutorial three, read the section on common features, skip down to the section on the foreground selection tool and finally continue to the section on Tutorial three, after the selection.
When creating selections, it is advisable to increase the magnification of the image; the plus and minus keys are handy for doing this. Note that this is not the same as changing the size of the image, which Tim cautions against in a later tutorial. You may also want to put the image into maximize mode, and press Tab to hide the toolbox and dock. This gives you a lot of room to work. Also, when you get to the edge of the screen, hold down the spacebar and the selection tool changes to a navigation tool, allowing you to bring different parts of the image into view. Releasing the space bar turns the tool back to the selection tool.
One can use every selection tool to create a new selection. If a selection already exists, one can choose to replace it with a new selection, or use a selection tool to add to, subtract from or intersect with the existing selection. This can be done by selecting the appropriate Mode in the properties box. Let the mouse pointer hover over the little rectangle to see the effect; click on the one you desire.
An important thing to remember is that a selection is not set in stone. If you create a selection that is nearly what you want, there are easy ways to modify the selection so that it is exactly right.
Here are some specifics about the individual tools.
Rectangular and Ellipse Select Tools
These tools create a rectangular and an elliptical selection. The respective keyboard shortcuts are R and E. They are great when you need this type of selection, but not much use in picking a flower out of a picture. More information on the tools is given in the help files http://docs.gimp.org/en/gimp-tool-rect-select.html and http://docs.gimp.org/en/gimp-tool-ellipse-select.html.
The Free Selection Tool
Also called the Lasso tool, it looks like a lasso and the keyboard shortcut is F. This tool allows the creation of a selection by holding down the left mouse button and moving the mouse pointer to create a selection. When the mouse button is released, the end and the beginning points are connected, completing the selection. I find that it is hard to use this tool to create precise selection. While not strictly a selection tool, the Path tool has similar attributes and offers more flexibility and accuracy. Read more about this tool at http://docs.gimp.org/en/gimp-tool-free-select.html.
The Fuzzy Select and Select by Color Tools
These tools operate in a similar way, in that they both make a selection by color with a single click of the mouse. The difference is that the Fuzzy Select, or Magic Wand tool, selects contiguous regions only, while the Select by Color tool checks the entire image. The idea is that all pixels whose color is “close enough” to the given color will be selected. Effective use of these tools depends on the proper selection of Threshold in the Properties box. A larger threshold means that more points may be selected, sometimes including points you may not wish to select. A smaller threshold means that less points are selected. These tools work well when there is significant contrast between the area you wish to select and the remaining area. The Fuzzy Select tool looks like a magic wand, and has keyboard shortcut U. The Select by Color tool has a finger pointing at three colored squares; keyboard shortcut Shift + O. Information about these tools may be found at http://docs.gimp.org/en/gimp-tool-fuzzy-select.html and http://docs.gimp.org/en/gimp-tool-by-color-select.html.
The Scissors Select Tool
This tool looks like a pair of scissors and has keyboard shortcut I. It is supposed to have the same function as Photoshop’s Magnetic Lasso tool described in Tim’s tutorial. I have found that the tool doesn’t work very well, and the GIMP help files http://docs.gimp.org/en/gimp-tool-iscissors.html agree. Fortunately, there are excellent alternatives to this tool.
The Foreground Select Tool
This relatively new and powerful tool looks like a person pulled out of a background image. It has no keyboard shortcut.
The tool works in several stages, and I will describe how to make a selection using the photo in Tim’s tutorial three. If you haven’t already done so, open this photo in the GIMP and click on the tool. A lasso will appear as if the Free Selection Tool were being used. Hold down the mouse button and trace a path around the flower, selecting as little of the background as possible. Try to stay outside the flower as you create the path. When you get near the start of the path, release the mouse button. The background will be covered by blue mask, and the tool icon changes to a paintbrush, indicating that the second stage is about to begin. Paint over the flower, trying to pick up all the colors. It looks like you are vandalizing the picture, but have no fear; this is a part of the process. When you release the mouse, you will see that the blue mask has enlarged. If some of it has covered the flower, repeat the painting process over the mask. Eventually, the flower should be the only area not covered with the blue mask. The final stage is to press Enter. There is your selection! (If it is not perfect, there are ways to fix it. Read on.) Learn more about this tool at http://docs.gimp.org/en/gimp-tool-foreground-select.html.
The Path Tool
Strictly speaking, this is not a selection tool, but it is extremely useful in creating selections. The tool looks like a barbell connected to the tip of a fountain pen; keyboard shortcut B. The path tool allows for the creation of objects called Bezier Curves. These curves start as straight lines, but can be dragged to form a smooth curve with up to two bends. One cannot expect to begin effective using this tool immediately, but with a little practice, it can become one of the most powerful weapons in the selection arsenal.
To start a path, select the tool, make sure that Design is selected as the edit mode in the properties box, and click on a point that should be on the border of the selection. This creates your first node. Move away from the node and a plus sign is appended to your mouse pointer. Go on a straight or gently curved portion of the desired border, and click again. If you get to a point where there is an abrupt change of direction, or if the curve gets too complex, click again. Eventually, you get over the starting node. The plus sign changes to a directional sign. Hold down control and the directional sign changes to a link. Click and you have a closed path.
You can now revise the path in a couple of ways. First, if a node is out of place, you can place your mouse pointer over it, click, and drag it. You can also drag the lines to conform to your desired curve. To do this, click on one of the lines. One or more handles will appear on each of the adjacent nodes. You can drag the curve or the nodes to move the curves. This is where practice is useful in mastering this tool.
Once you have a path, you can convert it to a selection by going to the Select menu, and choosing From Path. Alternatively, use the keyboard shortcut Shift + V. The Layers, Channels, Paths dock has a tab for the paths dialog. Unlike selections, paths persist throughout your session. The paths dialog has a list of all the paths you have worked on. Of particular importance is the red square in the row at the bottom. This allows for path to selection as above, but also gives the option to add to, subtract from or intersect with the current selection. So if you have a selection that is not quite right, you can create a little path, and add or subtract as desired.
More information on the path tool may be found at http://docs.gimp.org/en/gimp-tools-other.html#gimp-tool-path.
The quick mask can be used to fix imprecise selections. Assuming a selection exists, you choose it by clicking the dotted rectangular box at the lower left hand corner of an image. Alternatively, use the keyboard shortcut Shift + Q or the select menu. The area not chosen is then covered with a pink mask. One can then use paint tools, such as the paintbrush or pencil, to refine the image. Once a tool has been chosen, select the appropriate brush style and size from the properties box. Be sure that opacity is at 100%. If the foreground color is black, one can remove areas from the selection by painting over them. If the foreground color is white, painting non selected regions adds them to the selection. This tool can do a lot more, but that is beyond the scope of this tutorial. Read about it at http://docs.gimp.org/en/gimp-image-window-qmask-button.html and the subsequent links.
Tutorial Three, after the Selection
At this point, you have made a selection consisting of the flower. To invert the selection, use the keyboard shortcut Ctrl + I, or choose Invert from the Select menu. To feather the selection, choose Feather from the Select menu. You will be asked for the number of pixels; choose one as in Tim’s tutorial.
To perform a Gaussian blur, select the Filters menu, then Blur, finally Gaussian Blur. A menu comes up asking you to select the number of pixels. While the tutorial used a radius of 4.6 pixels, I found that it took 10 pixels to get the same effect in the GIMP. If the preview box is checked, you should see the effect of the change in the preview window. If the effect isn’t visible, move one of the scroll bars a little and you should be able to see it.
Notes for Tutorial Four
The GIMP does not have an adjustment tool as extensive as Photoshop’s Variations tool. However, I was able to do a good job of obtaining the same effect with the Color Balance tool. Go to the Colors menu, select Color Balance, and a menu pops up. One can select the range to work on, from among Shadows, Midtones and Highlights. It is possible to adjust all three of these attributes, one at a time. I started with Midtones, and moved the blue slider to 54. The color still seemed to be off a bit, so I went to shadows, and moved the blue slider to 16. (As Tim said in the tutorial, to remove the yellow cast, add more blue.) The color balance tool is described at http://docs.gimp.org/en/gimp-tools-color.html#gimp-tool-color-balance. Additional information about improving color in images is given at http://docs.gimp.org/en/gimp-imaging-photos.html#gimp-using-photography-colors
Be forewarned that the automatic tools mentioned in this discussion, while quick, rarely provide the desired effects.
A useful tool for judging the accuracy of a color correction is the Pointer Dialog. Access it from the Windows menu, then Dockable Dialogs, Pointer. I use this dialog often, so I have added it to my permanent Layers, Channels, Path dock. (See http://docs.gimp.org/en/gimp-concepts-docks.html for information on customizing a dock.) This dialog records the color, in the amount of red, green and blue, for the pixel currently at the position of the mouse pointer. I used this tool on the first picture in the tutorial. Specifically, I used the rectangular selection tool to select the bottom image, applied the adjustments in the first paragraph, and used the path dialog to compare the colors between the two flowers. There are lots of colors and the values in the dialog change rapidly, so I only looked for an approximate match. This tool is useful if one has a standard that may be used to compare the adjustments.
Notes for Tutorial Five
Access the Levels tool by selecting Levels from the Color menu. It works much like that Photoshop tool described in the tutorial. Where Photoshop says RGB as the Channel, the GIMP uses the word Value. The numerical values are not the same in the two programs. While Tim moved the left Input slider to 13, I found 32 to give better results in the GIMP. Similarly, for the middle slider, Tim used 0.83; I chose 0.76. In addition, there seemed to be too much contrast between the light and dark parts of the photo, so I slid the right Output slider down to 209.
As for the other tools in this tutorial, I used the Hue-Saturation-Brightness tool from the Color menu much as Tim did. There are Brightness-Contrast and Color Balance tools on the Color menu as well. They work in a similar manner to their Photoshop counterparts, although the numerical values of adjustments may differ.
Notes for Tutorial Six
The GIMP has a number of Auto correct tools, (Color menu, Auto, select from menu) none of which was particularly effective in correcting the color of the first image. The White Balance tool came the closest. The tools of Tutorials Four and Five can be used to correct the color manually.
The second image illustrated the Photoshop Shadow/Highlight tool; I could find nothing analogous to it in the GIMP. However, I was able to get the desired effect. First, use rectangular select to select the left hand section of the composite picture. Then from the Color menu, Levels. Using the value channel, move the middle slider left to a reading of 2.07. Then switch the channel to blue, and move the middle slider left to 1.10. Checking with the pointer tool reveals that the two sides of the images are very close. For the other pictures in the tutorial, I also used Levels to make the adjustments. While Levels does the job, it appears that the Photoshop tool is easier to use.
Finally, I found nothing in the GIMP that corresponded to the photo filter tools in Photoshop.
© 2009 by Dr. Robert Stanton - all rights