Lesson 9: Selection tools and options

When working with your images, you will eventually find yourself in situations where the proper selection will be absolutely critical in order to get the results you want. Sometimes the creation of the selection is a matter of precision, taking time and effort. You may need to elaborate a complex selection using different tools, with different options, and greatly zoomed in for detail. It may not be an easy job, but it can be rewarding for an image that is important for you. GIMP has intelligent tools to help you with this task.

After achieving your selection, you may

• affect the selected pixels with any tool,
• you may copy the selected data elsewhere or on another image,
• paste data inside your selection,
• you can even save your selection for later use.

The principle of progressive learning

There is one thing i would like to note at this point. This school is intended to introduce you with the possibilities of image editing and help you start with. Some aspects of the tools you are about to learn in this lesson extend beyond the expected abilities of a beginner, so inevitably they may represent a learning challenge. You are adviced to practice by experimenting on your own images, trying to apply what you have learned of other tools as well at the same time. When you do not understand something on a topic, do not worry, ignore for now the parts you do not understand, go on with the school, and coming back on this later again you will understand more.

Common options of the selection tools

Snapping to positions when operating with selection tools

Under the view menu, there are 4 toggle commands that can considerably enhance precision, both during selecting operations and also when moving selections you have already made.

The seven selection tools

Rectangle Select Tool

Ellipse Select Tool

With this you can create circular and elliptical selections. The options of this tool are the same as those of the Rectangle Select tool (except the rounded corners option). It works basically in the same fashion like the rectangle select.

You can use some key-modifiers when creating an elliptical selection. We have seen that pressing the CTRL key before starting the selection, you subtract from the existing selection. If you press the CTRL key after starting the dragging and hold it down till completing the dragging, this checks the "Expand from center" option. If you press SHIFT before starting the dragging, you add to the current selection, while if you press the SHIFT after starting the dragging and hold it down till finishing the dragging, you draw a circle. Combining CTRL and SHIFT, you create a circular selection starting from the center. In experience, these key modifiers seem to be a bit complex to use in some systems, and if precision is your concern in drawing tasks, the safest way to work is to draw guides with precision and then create your selections with snapping to guides enabled.

Drawing filled shapes and outlines

Free Select Tool

The free select tool, also called "Lasso", works in a quite smart way. It is simple to use but at the same time quite sophisticated. This tool is very effective to use with a drawing tablet. You can draw in freehand style with your pointer the edge of your selection. After some practice you will realize that it is convenient to firstly make a rough selection with it, and then refine the selection directly on the quick mask. This method will probably take you some time, but it may be rewarding for a project that is important to you - and as you will see soon you can save your important selections for reusing them. Freehand manipulations are easier to conduct with the stylus of a drawing tablet than with an ordinary computer's mouse.

Fuzzy Select Tool

The Fuzzy Select Tool -or Magic Wand- is a very smart and sophisticated and powerful tool, designed with the intention of selecting contiguous areas based on color similarity. This task is not a simple one by itself, and the nuances of this task reflect on the tool's options. It works relatively well in non-continuous tone images, but in photography it often causes frustration to beginners. I strongly recommend that

1. first you read carefully the documentation for this tool in GIMP's help file (no need to repeat) and then
2. you try it on your own images.

While it is a challenge for beginners, it can be a powerful tool in the hands of the advanced user who has understood the options and can work with it in predictable ways. It is one of the things that you will learn with experience and with the combined knowledge of other tools as well.

Select by Color Tool

This tool works in a similar way with the Fuzzy Select, with the difference of selecting not only the contiguous pixels but every pixel that obeys the color similarity rule in reference. I also recommend that you follow the same learning approach as for the Fuzzy Select, and still more to use it in the same cases to see the difference in action. There will be cases when this difference between the two tools is critical to achieve the selection result you want.

Scissors Select Tool

The Scissors Select represents one more challenge for a beginner. Its alternative name as Intelligent Scissors seems to be absolutely justified, since it can be an intelligent tool in the hands of someone who knows how to utilize it. It is so well elaborated that it might need a lesson by itself. It would not be wise to reproduce here the GIMP's documentation, which is well written and explains things very well, nor would it be wise to spend time watching videos explaining the nuances of this and that. So please face it as another learning challenge, read the documentation, and give yourself a bit of time to experiment. It is not difficult to understand, just practice with your images and you will soon get the hold of this tool as well. Note that usually after completing the selection, some refining on the Quick mask is needed.

The Scissors Select works relatively well when you want to separate areas with enough contrast in color/tone. This feature is the strongest point of this powerful tool. As exposed in Lesson 8, when there is not enough contrast in an interesting area on the image, it is wise to try to extract a secondary drawable with enough contrast in the specific area in order to exploit this contrast for a separation good enough.

The concept of selection (part II)

In the previous lesson i explained the concept of selection, describing what actually a selection is: an 8bit grayscale temporary channel. Repeat: If a selection was a spatial concept, that is to say simply refering to an area as a part of the canvas, that would be too simplistic. It can be that as well, but it is not just that, it is something more sophisticated and versatile. And much more interesting!

In the previous Lesson we used the concept of selection to its full power, considering it as an 8bit channel. Now we step back from the 8bit logic to the 1bit logic, considering the selection as a spatial concept. The seven selection tools work rather on a yes-or-no basis: a pixel on the layer is either selected or not selected. To test this, make a selection, shift to the quick mask view, copy the quick mask, create a new image from the clipboard: the image you see should be close to a black-and-white 1bit image.

As put in the previous Lesson, we can consider two types of selections:

• Continuous tone selections: selection channel values in the dynamic range 0-255.
• Non-continuous tone selections: selection channel values not in the whole dynamic range.

The seven selection tools make non-continuous tone selections. They work with the spatial logic. This is what they can do. This is why they work well with non-continuous tone images, but not so well with continuous tone images. However in photography as well they can be invaluable, but only in the hands of an experienced user, and usually on secondary drawables than on the image itself. To unleash the full power of selecting in photography, avoid the use of the selection tools on the image itself, instead pay attention to selective masking as explained in lesson 8.

Foreground Select Tool

This is the last of the seven selection tools. It is also very sophisticated, and again i prefer not to decribe it, it is well explained in GIMP's documentation, much preferable than watching long videos explaining the details and nuances (it has a lot of them). The basic idea is to separate an optical item based on color dissimilarity. It may work well with the subsequent help of the Quick Mask.

And, yes, i will never get tired reminding the importance of practicing on your own images. By experimenting on your own photos, you will benefit much and quickly on these sophisticated tools. After all that you have learned till now, you must know how to use the documentation, which is and will be important for your progress still after finishing this School.

The floating selection

Once upon a time when GIMP did not use layers, a "floating selection" permitted manipulations on a selected part of an image. Nowadays you can do wonders with layers, but the feature remained. A "floating selection" is a temporary layer that appears under certain circumstances, and it has the peculiarity that you must "anchor" it to the layer it originated in order to be free to work with any other normal layer. To be precise: you must incorporate/merge it on the drawable that was active when the floating selection was created. Of course in the meanwhile you can manipulate it as you want. You can make a selection floating with the command Select>Float [CTRL+SHIFT+L] but usually you do not need to do so, because you can work with normal layers at full power, as we will see in lesson 12.

A floating selection is created with pasting operations (Edit > Buffer > Paste Named..., Edit > Paste, Edit > Paste Into) or with the transform tools when used on a selection and not on a layer. The safest way to go for a beginner is this: if a floating selection ever appears on top of the layer list in the Layers dialog, just convert it to a normal new layer with either of these two ways:

1. RightClick on the floating selection > To New Layer, or
2. Layer > To New Layer [CTRL+SHIFT+N].

After that you will be free to handle the new layer to your heart's desire.

Useful commands that have to do with selections

Please practice these very useful commands by yourself on a few of your images, they are very easy to understand. Some of them apply mainly in drawing tasks and some in photography as well.

Select > All [CTRL+A]: creates a selection with the content of the current layer and inside the canvas, that is to say inside the layer borders and inside the canvas.

Select > None [CTRL+SHIFT+A]: deselects (cancels any selection).

Select > Invert [CTRL+I]: inverts the current selection. That is to say, inverts the selection channel values for the range 0-255. For example, a pixel with 0 gets 255, a pixel with 255 gets 0, a pixel with 5 gets 250. (Question: if nothing is selected, what will happen? Answer: it will be like you do Select > All.)

Select > Feather...: the command is available only if a selection is present. It softens the border of a hard selection. You can define the radius in the appearing dialog. It may be useful in many situations, like for example when copying image data, so that the data will be easier to incorporate in the destination image, creating a smooth transition between the item and the surrounding. After specifying the feathering radius, you can toggle to the Quick mask to check the amount of feathering.

Select > Sharpen: it does the opposite of the previous one, it removes feathering (if any), creating the edge at the marching ants, and removing antialiasing.

Select > Shrink...: does what it says actually, reduces the selected area towards the inside of it, preserving feathering, and as the documentation says "the shape of the feathering may be altered at points of sharp curvature". If you check "Shrink from image border", if the selection runs on edges it stays away from the edge.

Select > Rounded Rectangle: converts the existing selection to a rectangular selection, possibly with rounded corners. The new selection follows the outmost edges (top, right, bottom, left) of the old one. You can define the radius for the corners (if 0 you get an ordinary rectangle). You can define if the rectangle will be either concave or convex.

Select > Grow...: does the opposite of Select > Shrink.... As stated in the documentation, rectangular selections present a peculiarity: the new selection has rounded corners, so you follow up with Select > Rounded Recrangle with a radius of 0 and you are done.

Playing with "inline frames"

Now that we know some drawing commands, let us play a bit creatively, making frames in photos. As we have seen in lesson 2, you can add a frame to a photo by increasing the size of the canvas. "Inline frames" are interesting as well, as they present various aesthetic and technical challenges.

Select > Border...: creates a selection along the edge of the existing selection. You define if you want it feathered, and the width, half of it inside half outside the marching ants line.

Saving and reusing selections

You might ask, alright, but can i save selections? That would be excellent. Well, it is excellent. As we saw in the previous lesson, you can copy, paste and save directly from/to the Quick Mask, which means that it is easy to save independent grayscale images as selections. But you do not have to do this, since GIMP offers the possibility to save and operate with selections inside your project itself.

Creating a vignette

Note: the fill could be done on a separate layer for better versatility, i am now showing the most simple case logic.

Stroking a selection

In drawing, a stroke is a single movement of a pen or brush on the drawing canvas. In GIMP, you can stroke the border of a selection, and the stroke will follow the line of the marching ants. This is apparently at first useful for drawing. But still in photography as well, since GIMP offers various options for the stroking: to draw a simple line, to draw with a pattern, or to draw using any of its so-called "painting tools".

Edit > Paste Into: pastes the content of the clipboard "inside" the selection - that is to say data outside the selection is "rejected".