Making a masked picture with Gimp (2)
There are still more possibilties of making masks with Gimp. In total you can see here 10 ways to do it, try them all out and choose you favourite ones...
Method 6 - Invert
For this example, we use the same flower. In the layers window, we right-click and choose 'Add Alpha Channel" (for a transparant background)

Here we use again the Lasso Tool, but now we draw quickly a circle around the flower with the Lasso Tool, and close the circle, so that you obtain a dotted line around the flower. In the layers window, you will see the layer "free selection".

Go to the menu and choose : Select - Invert.
In the layers window, you will see the layer "invert selection". This option makes you select the background instead of the flower image , so we choose : Edit - Cut
For the rest you continue with the Eraser Tool.
Method 7 - The Scissors Tool

For this example, we use the same flower. The Scissors Tool is similar to the Path Tool. The difference is that the Scissors Tool is drawing the curved lines around the edges for you, instead of having to do the precision work yourself. You can consider it as an intelligent Path Tool. You just need to click the anchor points, and you don't even need to click in a corner, the scissor tool makes the connection to the next anchor point but draws the line along that corner.If there is few color difference between the flower edge and the background, then the line is sometimes incorrect. If a line is not ok, then you can select that line and add a new anchor point in between. And you can move that anchor point on the correct position. Then you continue with new anchor points.

When you have made the whole circle around the flower, and you have selected again the first anchor point, then there will appear a small circle above Scissors Tool.
Then click upon the flower, and the scissor tool-line will be replaced by a dotted line.
Then choose : Edit - Cut , and then Edit - Paste as : New Image.
Method 8 - Layer Mask

Here we start with the Lasso Tool or Scissors Tool. When you dotted lines appear, then go to the layers window and right-click upon the layer image and choose "Add Layer Mask". Then a window appears and here you choose : white (full opacity)., and click upon "add", and you will see in the layers window ,that there is now a white layer mask next to the layer image.

Now click upon the white layer mask (to select the mask).
Go in the menu and choose : Select - Invert. (we select the background instead)
Then go to the the black/white icon and choose black (as foreground).
Now click upon the "Fill Bucket Tool", and choose as options : "full colour fill" , and the affected area : "Fill whole selection". Now click with the Fill Bucket Tool in the background of the picture..
The background becomes transparant , and in the layers window, you will see that a black background has been added to the white layer mask.
Now go to the black/white icon and select black as foreground (white is background). In the layers window, we add a new layer ,and choose "background colour" (= white). In the layers menu, you move down the new white layer underneath the image layer, and the flower will appear on white background.
We add again and new layer and choose "foreground colour"(=black). Bring this new black layer also underneath the image layer. Now the flower appears on a black background.
By using the arrows in the layers menu , you can easily switch the background to black or white, just by moving the black layer above or under the white layer. With a white or with a black background, you have a clear view upon what needs to be removed.Go to the menu : Select - None . Now the dotted lines are deselected.
In the layers window , we select now the layer mask. (for the editing work)
And in the tools window, we select the Paint Brush Tool.
Double-click upon the Paint Brush, where you change the hardness and the size of the brush. We zoom in into the flower with the Ctrl + mousewheel . Go the the flower edges and add the black parts to the background, which don't belong to the flower.
If you go too far (inside the flower), then this can be solved easily. Switch the black/white icon into white foreground and use the Paint Brush Tool to erase the black parts. Here again, if you go too far, you switch again black/white icon again to black.

When you have finished with the corrections, go to the layers window, and delete the black layer and white layer. The flower with transparant background remains. Now choose in the menu : Image - Auto Crop Image . Or you can do this : In the layers window, you still have the image layer and the layer mask. Select the layer mask.Choose the Fuzzy Select Tool and click upon the flower. The flower is surrounded by dot lines. Go again to the layers window and select the image layer.And choose in the menu : Edit Cut , and then : Edit - Paste as New Image.

Now you just export the flower with .png extension.
Method 9 - The Quick Mask
Also with the quick mask , you can easily repair what you have removed too much.In this example, we use a clematis flower.
We click upon the square in the lower left corner ( = "quick mask") (or shift +Q )
Now the flower image is covered by a red layer mask.
Select the Pencil Tool (double-click to change the size and the hardness of the pencil ).
Click upon the black/white icon, choose white as foreground. Now use the Pencil Tool and make the flower visible, the background remains red.. Switch to black, then the Pencil Tool will add again parts to the background , that were removed. You can also use the Eraser Tool for that, but with the opposite effect, which means that if you have white as foreground, then the Erase Tool will add things to the quick mask background.
Zoom in for detailed editing work. If things aren't very clear with the red background, then go in the menu to : Select - Toggle Quick Mask, where you put the mask on or off.
When finished editing, click again upon the square in the lower left corner ("quick mask") , the red layer mask disappears and the flower is surrounded by a dotted line.!! Now choose : Edit - Cut / Edit - Paste as : New Image.
Method 10 - The Channel Layer

In this example, we use a kind of mimosa flower. This method is similar to method 3 (color-treshold) , and is used when cutting out is complicated , where foreground and background are mixed up with eachother (eg. hair, branches, fencing, grill ).

In the layers window, we first duplicate the layer.
If the flower is darker than the background, then choose in the menu : colors - invert. (For this example , we don't need to do this ). The purpose of this inverting is for the next step, where we will make a black&white image with a white foreground (of the flower) and a black background (= all that will be deleted and cut out from the image)
Go in the menu to : Colors - Components - Channel Mixer
The Channel Mixer window appers, and you see the 3 channels : the red , green and blue channel.
Now you select the word "monochrome", so that it is "checked" .
The picture in the Channel Mixer window become a black&white picture.
Now move the sliders of the red, green and blue color, so that you make the flower as white as possible and the background as black as possible. By moving the slider of the green color to the left, the green color is excluded and becomes almost black. And we maximize the red, so that the flower becomes totally white.
In most cases, you won't be able to make the background totally black, but we will fix that later. When you have the best result in the black&white window, click upon OK.
Now you will see the picture in black and white, and in the layer window, the layer has also changed into black&white, whereas you still have a duplicate of the original.
Go in the menu to : Colors - Levels. The Level window appears and on the input level line, you have 2 sliders . By moving these 2 sliders, you can exclude most of the remaining background. Click OK to close the window.
Go to the layers window, and select the image layer (with the picture) and right-click and select : add new layer. And you choose : white (not transparant) and choose : Add. Now you see a white layer behind the image layer. Now select the black&white layer and copy this layer (CTRL+C). Then select the white layer and paste (CTRL+Z). Now you see a new layer above the existing layers. Select that new layer, and right-click and choose : "anchor the layer". Now the white layer has become a black&white layer.
Now select again the upper black&white layer and click upon the eye-icon (in front), and now you see the flower image with a transparant background.
Now we zoom in with CTRL+mousewheel. Select again the image layer, so that we can modify things on the picture. And we use the Brush Tool and clean up the remaining parts of the background , because the background is not totally transparent yet: Some parts are still a bit yellow/grey, and you will see that in the masked picture if you don't remove them. You can use a fuzzy brush instead of a hard brush for parts close to the flower edges. Click upon the black/white-icon to switch .Then you can add parts of the image again with the Brush Tool.
Now we still have to modify the image size. Here we cannot use " Image - Crop to Selection", and not either : "Edit -copy / Edit - Paste as : New Image". But there is another possibility : go to the menu and choose : Image - Canvas Size. And you see the Canvas size window. You will see that the width is 493 pixels , the height is 349 pixels. We modify the width to 349 pixels, so that we obtain a square image.
Now you can move the flower image with your left mousekey to the middle, so that it fits into the box of 349x349pixels, and choose: Modify Canvas Size.
Finally you can export this as a .png-file. If you still see some background , then load the png file again, and use the brush tool again and remove the "almost invisible" background, and export again as a .png file.