What are layer masks:

A layer mask is a layer that is placed on top of another layer, so that a part of it is visible and the other part is invisible, and is therefore, transparent.
The portion that is in whit,e in a layer mask is opaque, and the part that is in black, is transparent.
All intermediate values of various shades of gray or anything else, are semi transparent.

 

Adding a Layer Mask

If you need to do add a layer mask, add a new Layer.
Whether this is a background layer or not, it does not matter.

In order to add to a layer, we have different options.

I think the quickest way, is to right-click on the place where you want to add a layer mask, and select the “Add Layer Mask” button in the drop-down menu.

This opens the dialog, “Add Layer Mask” (1).
In this dialog we have some choices. I will go over them once.
White: This is the white layer mask, which makes the whole image visible.
Black: This is the black layer mask, which makes the whole image invisible.
You can either use it a lot or just for a few times, depending on how you want to display an image.

“Layer’s Alpha Channel” and “Transfer Layer’s Alpha Channel”.
Both will take the alpha channel of the image and use it as a layer mask. The second option, “Transfer Layer’s Alpha Channel” will not only take the alpha channel, but will also use this information to further transform the mask and remove it from the layer. The first “Layer’s Alpha Channel” will not delete information from the layer, so you yourself will have to adjust it to the layer, and not to the mask. We shall see more about alpha channels in a later lesson.

Selection: You can add a layer mask based on a selection. Everything that is selected becomes white, so it is displayed, and everything that is unselected, becomes black, and is therefore hidden.
Grayscale copy of a layer: the layer will create a grayscale image, and use it as a mask.
Channel: When you have selected a channel, you can use this channel as a mask.

The checkbox “Invert Mask” will mask the other portion, which is currently un-masked.
For example:
If you have made a selection, and you do not want this selection to be masked, but you want all the rest, you can select this check box.

 

In this first example I will add a layer mask based on a selection.
What I need is a selection to do this.
I select the flower, which is an easy task.
Then I right click the layer and select “Add Layer Mask” in the drop-down menu.
I select “Add Layer Mask” in the “Selection” dialog and click the “Add” button.
Now, everything that is selected in the layer mask is white and opaque, and everything that is not selected in the layer mask is black, and thus completely transparent.

 

I can’t see anything on a background that is completely transparent, so I open a second picture, and copy and paste it in the first picture.
I think you already know how to do this, but I will go over it once again.
Click “Edit” in the menu bar of the second picture, and select “Copy” from the drop-down menu.
Then, once again, select the first picture, which is that of the rose.
Click “Edit” in the menu bar of the image, select “Paste” in the drop-down menu, and click “New Layer” in the drop-down menu.
Drag the new layer below the layer with the layer mask.
Then we get the following result.

 

We’re going to add a photo.
To do this, we open the third photograph, and copy and paste it as a new layer in the compilation photo with the rose.
Click and drag this new layer, all the way down (1).
Then we add a layer mask to the layer with the flowerbed.
This time I select “White” in the selection menu of the “Add Layer Mask” dialog.
This makes the layer opaque, so we can have a black layer mask, or a grayscale one.
For this, select the “Gradient” tool in the toolbox. Otherwise, set the foreground and background color to “Black / White,” and select “Linear” in the options window.
If not, select the layer mask by clicking  this button (2) and then click and drag the image, in whichever direction you want and that does not matter as long as you know that “white hides,” “black shows “.We now get the following result. I leave it up to you whether you like it or not.

 

Suppose we still want to modify the picture.
We want to add a picture of our youngest child.
So, open this picture, then copy and paste it into the compilation with the rose.
Drag the new layer with the photo of the child to the top (1), and add a layer mask (2). This time I select a black layer mask. This displays the entire layer.
Then I select the “Gradient” tool , set the shape to “Radial” and click and drag in the image.

This isn’t so bad, I think, and it takes only about two minutes.

 

Deleting a Layer Mask

To remove a layer mask, right-click the layer with the layer mask and select “Delete Layer Mask” in the drop-down menu.

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