GIMP's Select By Color Tool can be a fantastic way to quickly and easily select areas of an image that are a similar color. In this example, I show you how to select part of a picture in order to change the coloring a little.
The final results aren't perfect, but this will show you how to start using the Select By Color Tool so that you can experiment with creating your own results.
1. Open Your Image
Your first step is to select an image that you want to experiment on and open it in GIMP. I selected a macro shot I took of a moth stood upon some black and purple colored wool as I thought this would be quite a good example of how the Select By Color Tool can make complex selections easy.
In this example, I'm going to change some of the purple color to a light blue. It would be near impossible to make such a complex selection manually.
2. Make Your First Selection
Now you click on the on the Select By Color Tool in the Toolbox. For the purposes of this exercise, the Tool Options can all be left to their defaults, which should match those shown in the picture. To use the tool, look at your image and choose an area of the color that you want your selection to be based upon. Now click on that area and hold the mouse button down. You will see a selection appear on your image which you can adjust by moving the mouse. To make the selection larger, move the mouse to the right or downward and move it left or upwards to reduce the size of the selection. When you're happy with your selection, release the mouse button.
Note: Depending on the size of your image and power of your PC, this may take some time.
3. Extend the Selection
If your selection, like the one in the example here, doesn't contain all of the areas that you want, you can add more selections to the first. You need to change the Mode of the Select By Color Tool to Add to the current selection. You can now click on areas of the image that you want to be added to the selection as necessary. In my example, I had to click on two more areas to achieve this final selection.
4. Remove Part of the Selection
You may just see in the previous image that some areas of the moth were included in the selection, but I only want to select the background. This can be remedied by removing some of the selection. I took the easy step of selecting the Rectangle Select Tool and changing the Mode to Subtract from the current selection. I then simply drew a rectangular selection over the part of the image that contained the moth. That gave me good enough results, but if you need to take similar steps in your image, you may find the Free Select Tool could be better for you, allowing you to make a selection more suitable to your image.
5. Change the Color of the Selected Areas
Now that you've made a selection, you can use it in different ways. In this example, I chose to change the color of the selected areas. An easy way to do this is go to the Colors menu and click on Hue-Saturation. In the Hue-Saturation dialog that opens, you have three sliders that you can use to adjust the Hue, Lightness and Saturation. I've adjusted the Hue and Lightness sliders to change the original purple color to a light blue.
6. Deselect the Selection
The final step is remove the selection, which you can do by going to the Select menu and clicking None. You can now see the final result more clearly.
GIMP's Select By Color Tool won't be perfect for every situation. Its overall effectiveness will vary from image to image; however, it can be a very quick and easy way to make quite complex selections in images that contain distinct areas of color.