GIMP Selection Tools

Transcription

1 GIMP Selection Tools In the lessons up to this point we generally have worked on modifying an entire image. In this lesson you will learn how to select specific portions of an image so that you can adjust this portion without changing the rest of the picture. Selection Tools The Selection Tools allow you to select a portion of the image to work with. GIMP has several selection tools. We will work with three of them in this lesson Red-Eye Removal If the flash attachment on your camera is close to the lens, the reflection of the flash off the blood vessels in the retinas of your subjects eyes often makes their pupils appear red. Some cameras have a red-eye reduction feature, but this feature frequently does not work perfectly (or at all, in my estimation). Luckily, GIMP has a red eye removal tool to get rid of the red eyes. Open the picture, RedEye.jpg, which is badly in need of red eye removal. Set the Zoom tool to magnify the image to at least 400% and focus on the eyes. Elliptical Selection Tool We need to tell GIMP where the red eyes are. Choose the Elliptical Selection Tool from the Toolbox. Choose the Add to Selection mode for this tool. Lesson 5 GIMP -- Selections 1

2 Use the tool to select a roughly circular area that surrounds the entire pupil of the eye. Larger than the pupil is OK just make sure you get it all. Do the same for the other eye. The second circle does not need to be the same size as the first, as long as it completely surrounds the pupil. Select Filters, Enhance, Red Eye Removal tool from the toolbar.main menu. In the dialog box that appears, magnify and move the image around inside the preview box until the eyes are shown. Move the threshold slider until the pupils becomes dark. Click on OK. If you are not satisfied with the removal, Undo the change and try again. Lesson 5 GIMP -- Selections 2

3 Lasso Selection Tool The Lasso Tool allows you to select an irregular region. It is a very useful tool and the one I use the most. We will use it here to select an irregular object that we want to move to another place on an image. Open Airplane.jpg and save it as Airplane.xcf. I was premature when I photographed the airplane and captured its image when it was slightly overlapping the wooded hill. I would like to move the airplane away from the wooded hill to somewhere close to the intersection of the rule-of-thirds lines in the upper right corner. This is cheating, I know. Who cares? It makes a better picture. Zoom in to 400% so that the airplane almost fills the window. Lesson 5 GIMP -- Selections 3

4 Choose the Lasso Tool from the toolbox. Click somewhere near the plane and carefully draw a line around the plane s picture. The area selected should be slightly larger than the plane. When you have completely surrounded the plane and bring the lines together, they will turn into a dotted line showing the selection. (You will select a portion of the trees. Don t worry about it.) Copying and Pasting Select Edit, Copy from the main menu. This will copy the selected portion. Select Edit, Paste from the main menu. This will place a dotted rectangle around the selected area as well. It is not obvious, because the pasted image is the same as the original, but you now have two images of the airplane in your picture, the pasted version directly over the original. We now will move the pasted airplane, which is on top, to the place in the picture where we want the airplane. Then we will remove the original one. Lesson 5 GIMP -- Selections 4

5 Moving a Selection Select the Move tool from the toolbox. Change the Zoom to 100% and use the Move tool to move the pasted selection to the desired place in the image. At this point, there will be two airplanes in the picture the original one and the pasted one. Use the Eraser tool to erase any vestiges of the trees in the pasted region. Use the Clone tool to remove the original airplane. Save the image as an xcf file. Feathering a Selection Feathering a selection blurs its edges so that the transition between the selected and unselected regions is not as abrupt and is less obvious. We didn t need to do this in the above example because the sky around the airplane was all about the same color. If we had needed to feather the selection, thought, we would have done the following: Select Select, Feather. Then choose the amount of blurring you want. Lesson 5 GIMP -- Selections 5

6 The Scissors Selection Tool You may want to select a non-rectangular area that is bordered with straight lines. The Scissors Tool, which uses intelligent edge-fitting is a good choice for this kind of situation. Open Posters.jpg and save it as Posters.xcf. Prepare the photo using some of the techniques we learned in earlier lesson: Adjust the brightness and contrast with Levels Automatically correct the color balance. Crop the photo to look something like the illustration at the right. We would like to emphasize two of these posters to help them stand out from the others. One way of doing this is to selectively saturate the colors in these two posters. First, we want to select the Álbert Hill poster an irregular shape with straight borders. Zoom in to 200% and focus on the Albert Hill poster. Then choose the Scissors selection tool. Click on the upper left corner of the Albert Hill poster. You should see a small circle on this corner. Lesson 5 GIMP -- Selections 6

7 Now click on the lower left corner. You should see a second circle there and a line connecting the two circles that follows the edge of the poster. Continue this process until you have selected the entire border of the poster by licking again on the first circle. Click on the poster. You now should see that the poster is surrounded by a dotted line, indicating that it has been selected. Use Colors, Hue-Saturation to increase the saturation of the selected area. After clicking OK, choose Select, None from the main menu to deselect the poater. Saturate the colors in the Dezeray s Hammer poster in the same way. Lesson 5 GIMP -- Selections 7

8 Practice Problems Plan how you would improve the following images and then make the improvements using the workflow we have developed. 1. Dress.jpg Straighten the image Lighten the midtones with Levels Correct the color Remove the pole and wire o This may require Paint tools as well as the Clone Stamp Select the Orange triangle at the bottom and desaturate it without doing anything to the rest of the picture 2. Peshtigo.jpg Crop the image so it looks like the picture at the right. Adjust the brightness with Levels Zoom in to 800%. Focus on the image of the kayaker. Use the Lasso Tool to select the kayaker. Selectively saturate the kayaker so that he is emphasized in the picture. Lesson 5 GIMP -- Selections 8