Define layer masks in Adobe Photoshop
Here we are going to focus on layer mask in Photoshop cs5 but first take a look on
What is layer mask
Layer mask is a like overlay that you add to a layer in order to hide part of that layer from view. To show you that I made a image for you has contains 2 layers 1 of which contains layer mask.
In the layer panel I am going to click the eye icon to the left of top most layers. So that you can see the content of that layer below. Now I make the top layer visible again by clicking its eye icon field the top layer is completely filled with blue pixels.
but you don’t see all of the blue pixels in document window because this layer contains layer mask which is represented by this thumbnail. The thumbnail on the left represent the image pixels the thumbnail on right represents the layer mask. I am going to make this layer mask temporarily invisible by holding down the shift key and clicking on this thumbnail so that you can see with out the layer mask the layer completely fill with one color.
now I going to make layer mask visible again by clicking on layer mask. To give you better sense of what layer mask is made up of I am going to show you layer mask in document window hold down the Option key on Mac or Alt key on pc and click on layer mask thumbnail and that displays layer mask here in document window.
Layer mask is grayscale Picture that means that layer mask contain only black pixels white pixels or in some cases pixels that shades some grey where the layer mask is black it hides the content to a layer to which it is attached and where the layer mask is white it show the content of the layer to which is attached and where the layer mask is grey. It partially show the content to which is attached.
Let’s go back and look in the image again I go to the layer panel and hold down the option key on Mac or Alt key on PC and click again on layer mask thumbnail to see the image inside the document window.
So this is the area where black pixels on the mask and on the outer side there is white pixels on the layer and in between there are some grey pixels attached to layer, so that's what layer mask is A grey scale over lay hide parts of layer from view but why use layer mask at all you may be wondering in this case I didn’t take eraser tool and erase this portion of the top layer. Read about layer's in Photoshop.
“blue “or why didn’t select this portion with selection tool and delete it form the file the answer in Photoshop its always good to work in a way is non destructive of your image that way you have flexibility to come back in and change your mind. when you add layer mask like this one to a layer you are not erasing or deleting pixels you are just covering them up temporarily and that means you can change your mind and back and reveal those pixels again so the power of layer masking that allows you work non destructively hiding content without permanent deleting or erasing it and allowing you to come back to change your mind any time your layer mask will stay with the file as long as you save the image that support layers in the Picture.