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Understanding Layer Masks
Posted by: Flora on 12-31-1969.

"A beginners Tutorial for better understanding Layer Masks in Photoshop "


A lot has been written on the topic 'Layer Masks' : what they are, how to create them, when-and-how to use them, and their incredible power (see Vikki's excellent Tutorial).

Still, they can be a big mystery for anyone starting out with Photoshop or any other image manipulation software which offers this great feature!

So, this tutorial is for the 'newbies' in image retouching/restoring .... who, like many of us at the very beginning, felt their heart sink when, following instructions, came to the point: create a black (hide all) Layer Mask ....
Well, I thought, ... what is this 'everything' a Black Mask is supposed to hide ... and... if it hides EVERYTHING, what's the point in creating it?!?!? :o:

Last famous words as Layer Mask is one of, if not THE feature I use most when working on pictures!!!!

Layer Masks are, actually, about Selections .... any kind of Selection .....for any kind of 'selective' correction ... they are very versatile and flexible and, to quote Vikki, their power is  simply awsome .....


Of course, any selection and relative correction/change can be made directly on the Layer .... fact is once this change is submitted there's no turning back  ... If we don't like the result we simply have to start from scratch ...
Working with Layers and Layer Masks lets you retrace your steps to the point of the 'wrong' correction, fix it, and continue from there ... In many cases, this can be achieved by just a few strokes on the Layer Masks created along the way.

Layer Masks can be created for/added to active/highlighted Layers only (not for the locked Background) by:

  • clicking on Layer>Add Layer Mask>Reveal or Hide All from the Layer Menu on Photoshop's top bar. (Image 1).

Image 1

  • clicking on the 'Add Layer Mask' icon at the bottom of your Layers Palette. (default: White=Reveal All unless a selection has been previously made) (Image 2).

Image 2

BLACK?? WHITE?? ....  

The following are Photoshop default colours for Layer Masks :

Black Layer Mask = Hide All
White Layer Mask = Reveal All

perhaps, the thoughts behind this were in the line of:

Black = darkness = no visibility
White = light = visibility

Anyway, it is according to these defaults that, whenever and however a selection is made, Photoshop automatically creates the right Layer Mask which becomes visible as soon as we choose to 'add' it to our working Layer... This particular Mask will be Black and White .... meaning ... the white on the Mask represents our selection, the area of the picture we will be working on/correcting .... while the black represents the 'rest' of the picture which we want to leave untouched ...

Enough 'rambling' .... let's see how all this works in practice ....

One of my first experiments in 'selective' corrections had been changing eye colour ... :wink: ....

Important!!! NEVER work on your original .... ALWAYS make a working copy first and rename it to be on the safest side!!!

  • Open your working picture and duplicate the Background by 'dragging' it on the 'Create a new Layer' icon at the bottom of your Layers Palette. (Background copy>Image 3)


Image 3

Let's start with a little experiment to see if and how this 'Layer Mask thing' really works ....

  • Click on/activate your Background,
  • click on the 'Create a new Layer' icon at the bottom of your Layers Palette to add a new blank Layer  (Layer 1) between Background and Background copy, (Image 4


Image 4

  • fill the newly created blank Layer with a colour of your choice. (Image 4a)


Image 4a


  • Click on/activate your Background copy,
  • add a Layer Mask by clicking on the 'Add Layer Mask' icon at the bottom of your Layers Palette. (it will be a 'default' White Mask - Image 5)
  • .... See? .... No difference at all!!! your Background copy is still fully visible and covers completely what is below.


Image 5


  • Now, click on/activate your White Mask,
  •  press Ctrl+I to 'invert' your mask which should turn Black.
  •  .... Wow ... see? ... your Background copy has disappeared and all you can see is the 'coloured' Layer 1!!! ...
  • Don't worry ... your Background copy is still there ... it has only been obscured/hidden by the Black Layer Mask. (Image 6)


Image 6


If you don't believe it, try this:

  • Making sure that your Mask is activated (an activated Mask has a double white border around its edge (Image 7)


Image 7

  •  ... that your Foreground Colour is white (Image 8), that  Opacity and Flow of your Brush are set to 100% and the 'Airbrush' capabilities  are disabled. 

Image 8

  • simply paint over your image .... amazing ... the white paint has uncovered/revealed part of your Background copy, the rest of which is still partially hidden by what's left of the Black Mask! (Image 9)


Image 9


  • and now, press X or Shift+X to change the colour of your Brush to Black,
  • paint black over the white area you had painted before to re-hide what you had uncovered or, better still, to decrease/refine the revealed area ....

On a White Layer Mask, just do the opposite:

  • paint black to cover/ hide,
  • paint white over the black to re-reveal, decrease/refine the hidden area ....

Let's now try something different to test the "awsome power" of a Layer Mask on a previously made selection ....

Let's start again with the working  picture and duplicate the Background.

  • Working on the duplicate Layer (top one), use the selection Tool you feel most comfortable with, to make your selection around the iris. (Image 10)


Image 10


  • With the selection active (marching ants around it), add a Layer Mask by clicking on the 'Add Layer Mask' icon at the bottom of your Layers Palette.
  • As I mentioned above, in this case, Photoshop will perform its 'magic' by automatically creating the appropriate Black and White Mask.  (Image 11)


Image 11


TIP: if you want to see what your Mask looks like, keep your 'Alt' key pressed while clicking on the Mask (Image 12) ... repeat the procedure to reverse the effect. (I feathered my selection to 'soften' it, that's why it's so blurred at the borders)


Image 12


As soon as you add the Mask to a Layer with a previously made selection, your 'marching ants' will disappear ... this means that if you wish to further adjust that particular area of your picture, you'll have to reselect it .... Nooo...I don't mean going through the selection procedure again .... by reselect I mean keep your 'Ctrl' key pressed while clicking on your Layer Mask and, as by magic, your selection and marching ants will be back and ready to be applied to the next Layer or Adjustment Layer...

That is what I did with the Selective Colors Adjustment Layer I used to change the eye colour in my picture... but, let's see the different Options for a practical example:

  • White-Reveal All (the changes made)   .... the overall changes gave the  image, but particularly the skin an unpleasant 'muddy', cyan cast. (Image 13)


Image 13

  • Black-Hide All (the changes made)  ... all the effects of the Adjustment Layer are hidden by the Mask and therefore invisible. (Image 14)


Image 14

  • Black and White = 'selective' Layer Mask ... the only visible change is the colour of the irises  ... result I was aiming for... (Image 15)


Image 15

.... the final result. (Image 16)


Image 16

If you haven't fallen asleep yet, there is one final section I'd like to add to this 'neverending' Tutorial:


We have seen Black and White Layer Masks and Black and White 'paint corrections' for hiding or revealing.

Between these two extremes, there is the whole Grey gradation which can be used on the whole Mask or on the 'paint corrections to gradually increase/decrease the strenght of their visibility. (Image 17)


Image 17

Finally, using a Black to White Gradient on a Layer Mask, results in a smooth, gradual blending of top and underlying Layers ....

This last procedure is very useful for smoothly blending two pictures together (Image 18, 19), and for creating collages.


Image 18

Image 19

I hope this tutorial has helped understanding Layer Masks better, so that, now, you might be tempted to use, experiment or, as I often say 'play' with this incredible feature!

Flora. :)

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