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Select By Colour 
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Extract An Object From Its Background (GIMP’s Select By Colour Tool)
GIMP (GNU) -
Intermediate Plus

Select By Colour Tool GIMP (Extract An Object From Its Background)

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This GIMP (GNU) tutorial demonstrates how to extract an object from its background using GIMP’s Select By Colour Tool. To work along, you are welcome to download the Start Image I am working with HereUnzip the file and open the Start Images onto GIMP’s workspace.

Notes
You can quickly Undo a step at any time by pressing Ctrl then Z. Alternatively, click a previous Undo History snapshot - Windows then Dockable Dialogues then click Undo History. In addition, to Zoom in (or Zoom out) of your image; from the top menu, choose View then select a Zoom Tool from the subsequent drop-down list.

Launch GIMP & Organise Its Workspace & Palettes

Note
Ensure the Layers and the Undo History Palettes are visible, and then drag them into position over your workspace - (Windows then Dockable Dialogues - then click Layers and Undo History).

Select By Colour Tool Notes
The Select By Colour Tool can make life very simple for you in cases where you want to select all the areas of an image that are the same colour, perhaps to edit that colour without affecting the rest of the colours in the image. The Select By Colour Tool is very similar in operation to the
Fuzzy Select Tool; the main difference being that the latter only ever produces single continuous selections, whereas the Select By Colour Tool will select all the areas in an image that are similar to the target colour and so may produce multiple disconnected selections.

1/
Open your choice of Start Image onto GIMP’s workspace - File then Open - Ctrl then O.



2/
Then from the left-side Toolbox, activate the Select By Colour Tool.



And, if you are working with my Start Image, set the following settings into The Options Box.



Further Select By Colour Information Is Available Here


Now, left-click once over the image’s (black) background - as illustrated below.



Left-click Note
If left-clicking once over your Start Image’s background doesn’t isolate the object with a Selection Marquee; then you need to keep left-clicking until your object is isolated completely by a Selection Marquee.

After your object has been completely isolated by a Selection Marquee, you are ready for the next step.

3/
Now, from the Layers Palette, right-click over the Background Layer and select Add Alpha Channel from the subsequent drop-down list.



4/
Then from the top menu, choose Select and then choose Grow. And from the subsequent Grow Selection dialogue box, set a Grow selection by setting of 2, and then click OK.
 


Note
For personal results, experiment with different Grow Selection values.
 


5/
It’s time to remove the Pepper’s Background. Therefore, from the top menu, choose Edit and then choose Clear - or tap your Delete Key. Because you created an Alpha Layer back in Chapter 3, after clicking Clear, the isolated (black) Background area will be removed. 

Removing the background reveals the following Chessboard Transparency. The Chessboard Background is GIMP’s way of informing you that the background is Transparent

Congratulations, you have successfully removed your object’s background using the Select By Colour Tool.
 




6/
From the top menu, choose Select and then choose None.



Drop Shadow Tip
My
Tutorial Here demonstrates how to apply a Drop Shadow - Filters then Light and Shadow then Drop Shadow.

Transparent GIF Tip
Link Here to learn how to save your Transparent Image as a Transparent GIF.

Fill Layer Tip
My
Tutorial Here demonstrates how to create a Fill Layer and Fill it with either a Solid Colour, Pattern or a Gradient.

                          

Select By Colour Tool GIMP


7/
To finish, from the top men, choose Image and then choose Merge Visible Layers.

                 

8/
Congratulations, your extracted image is complete, to and is ready to
optimise and save.

Now you are more familiar with this technique, you can have lots of fun removing backgrounds from your favourite objects.

Mode
As with most of the selection tools, the Select By Colour Tool offers four modes, defaulting to Replace the current selection. The other modes, Add to the current selection, Subtract from the current selection and Intersect with the current selection allow the Select By Colour Tool to make multiple selections that are combined to make a more complex final selection. One example might be making selections based on two distinct colours.

Antialising
This gives the selection's edge a more natural appearance and is the preferred option in most uses. If this is deselected and you zoom in to look at a selection, its edge will appear to be harsh and blocky.

Feather Edges
This allows you to give a selection a very soft edge that gently blends out like a gradient. When the tick box is checked, a slider is displayed allowing you to adjust the amount of feathering applied.

Select Transparent Areas
This allows the selection to contain completely transparent pixels if they fall within the Threshold that has been set.

Sample Merged
This will only affect images with more than one layer where the target layer's Opacity is less than 100 or the layer's Mode is set to anything other than Normal. In that case, the appearance of the layer's marked, the selection will be based on the composite effect of all the layers, whereas if it is unmarked only the colours of the target layer will be used to form the selection.

Threshold
This determines how similar a colour must be to the selected pixel before it is included in the selection. The further to the right the slider is set, the larger the final selection will be.

Select By
This drop down menu offers a few variations on how the selection is made. In most cases, the Composite option will be best, as that most closely matches what your eye sees, but there may be cases where you wish the similarity of colour to be calculated on a specific aspect of the visible colour. The possible options are to match by Red, Green, Blue, Hue, Saturation and Value.

Wendi E. M. Scarth. 
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