Advanced masking using a channels in Adobe Photoshop

Course contents
SECTION: 8
CC Libraries 19:15

Questions

1
You are not following this thread
1
You are not following this thread
1
You are not following this thread
1
You are not following this thread
2
You are not following this thread
1
You are not following this thread
4
You are not following this thread
4
You are not following this thread
0
You are not following this thread
1
You are not following this thread
0
You are not following this thread
0
You are not following this thread
0
You are not following this thread
0
You are not following this thread
0
You are not following this thread
1
You are not following this thread
0
You are not following this thread
0
You are not following this thread
0
You are not following this thread
1
You are not following this thread
0
You are not following this thread
0
You are not following this thread
7
You are not following this thread
0
You are not following this thread
0
You are not following this thread
0
You are not following this thread
0
You are not following this thread
0
You are not following this thread
0
You are not following this thread
0
You are not following this thread
12
You are not following this thread
0
You are not following this thread
0
You are not following this thread
0
You are not following this thread
0
You are not following this thread
0
You are not following this thread
0
You are not following this thread
0
You are not following this thread
0
You are not following this thread
0
You are not following this thread
0
You are not following this thread
0
You are not following this thread
1
You are not following this thread
0
You are not following this thread
0
You are not following this thread
0
You are not following this thread
0
You are not following this thread
1
You are not following this thread
0
You are not following this thread
0
You are not following this thread

Course info

107 lessons / 16 hours 21 projects Certificate of achievement

Overview

Course Overview

Hi there, my name is  Dan and I am an Adobe Certified Instructor for Photoshop  - this is the Advanced Photoshop course.

This course is not for people new to Photoshop. This is for people who already know the fundamentals. It is for people who have their own ways of doing things but believe there really is a better, faster way to work. 

We will start by learning the best selection techniques available. I promise, by the end of the first section what took you 30mins to mask will now take you 30 seconds. 

What am I going to get from this course?
  • 13+ Hours of content!
  • 10+ Interactive exercises
  • 68 downloadable resources
  • You'll learn the best selection and masking techniques
  • You'll know how to fix images that look 'hard to fix'
  • You'll master advanced levels and curves tricks, specifically with skin, adjusting and enhancing colors
  • You'll learn how to enlarge images without distortion and what to do when things go wrong
  • You'll know how to convincingly remove all kinds of objects from images
  • My favourite: You'll master the ability to distort, bend and reshape images
  • Lets look at how current trending styles are super easy to duplicate
  • You will become a type nerd. We'll use font pairing in Typekit. We'll also use Photoshop's ability to guess fonts
  • Your Artboards skill will be mastered
  • A master of retouching, you will become!
  • You'll learn to edit videos in Photoshop, who'd have thought?
  • We'll also create awesome cinemagraphs, AKA: Moving pictures!
  • You'll learn to master 3D in Photoshop!
  • You'll learn lots about professional, reusable mockups, techniques and shortcuts!

Here's some of the things we'll be doing in this course:
We will correct 'hard to fix' images and learn what to do with blurry images. We will master Advanced Levels & Curves tricks and will work specifically with skin, adjusting and enhancing colours. 

You will learn how to enlarge images without distorting them and also, what to do when things go wrong. 

We will learn how to convincingly remove all kinds of objects from images. My personal favourite section will show you how to distort, bend & reshape images.

We will look at how current trending visual styles are easily created, duotones, glitches and orange/teal colour grading.

We get 'type nerdy' and use font pairing in Typekit. We will use Photoshop to identify the fonts used in an image and learn how to work with hidden glyphs & ligatures as well as variable & open type fonts.

You will master artboards while you are learning how to make easily updatable multiple sized social media & ad banner graphics. 

There is a big section on advanced retouching techniques, advanced healing, advanced cloning & patching. 

You will learn how to edit videos in Photoshop. We will also animate static images creating parallax videos plus the very cool cinemagraphs sometimes called 'living pictures' - great for social media. 

You will learn to master 3D in photoshop. We will finish off the course with professional, reusable mockup techniques & shortcuts. 

This course has a strong focus on workflow. We use real world, practical projects and show you the professional techniques and shortcuts which will save you hours using Photoshop. Throughout the course I have many class exercises for you to use in order to practice your skills. 

Who am I? 
As well as being an Officially Certified Expert by Adobe, I’m photoshop guru and user with 18 years Photoshop experience. I make tutorial videos directly for Adobe and will again this year be presenting a seminar on  Photoshop at Adobe’s 20 thousand attendee strong Max Conference.  

If you can’t remember the last time you sat down and went through the updates in Photoshop, let this course be your one stop professional development and upgrade path.   

Even if you consider yourself a heavy user, I promise there will be things in here that will blow your Photoshop mind. Sign up now!

Course duration 13 hours 45 mins + your study.



Daniel Walter Scott

Daniel Walter Scott

Founder of Bring Your Own Laptop & Chief Instructor

I discovered the world of design as an art student when I stumbled upon a lab full of green & blue iMac G3’s. My initial curiosity around using the computer to create ‘art’ developed into a full-blown passion, eventually leading me to become a digital designer and founder of Bring Your Own Laptop.

Sharing and teaching are a huge part of who I am. As a certified Adobe instructor, I've had the honor of winning multiple Adobe teaching awards at their annual MAX conference. I see Bring Your Own Laptop as the supportive community I wished for when I was first starting out and intimidated by design. Through teaching, I hope to bring others along for the ride and empower my students to bring their stories, labors of love, and art into the world.

True to my Kiwi roots, I've lived in many places, and currently, I reside in Ireland with my wife and kids.

Certificates

We’re awarding certificates for this course!

Check out the How to earn your certificate video for instructions on how to earn yours and click the available certificate levels below for more information.

How to earn your certificate

Work your way towards your certificate for this course by following these simple steps.

  • Watch the course videos
  • Complete the Class Projects - look out for the videos marked with
  • Upload your class projects into the My Projects area in your account
  • Complete and pass the Knowledge Quiz (Merit level courses only)
  • Complete the Distinction Certificate Project (Distinction level courses only) - look out for the video marked with
  • Upload your Distinction project to the My Projects area in your account
  • Request your certificate when you've completed the requirements for the certificate level you're working towards

Good luck!

Pass certificates

We're awarding 'Pass' level certificates for this course.

You can work your way towards your 'Pass' certificate by following these simple steps.

  • Watch the course videos
  • Complete the Class Projects - look out for the videos marked with
  • Upload your class projects into the My Projects area in your account
  • Don't forget to request your certificate when all your projects are complete

Good luck!

Downloads & Exercise files

Transcript

Hi there, it is time for another selection tool in your arsenal, and it is the mighty Channel Mask. It's been around a while, and it's perfect for when you need to select, say out of focus grass like this. There we go, easily done, but let's say you already know how to do a Channel Mask, don't worry, there's some stuff in here for you as well. Imagine if there was a brush we could just kind of, like paint across and remove all the ghosting. It is true, my friends, this brush exists, and I will show you in this next tutorial. Let's get in there. 


It's getting better, we're going to love the brush. First up, let's open up our files, they're in our '02 Selections & Masking'. And it's all of these guys, it's Channel Mask 01, all the way through to 05. Quick little tip before we get going, if you hold down 'Ctrl', and hit 'Tab' on your keyboard, you can cycle through the open tabs along the top here. That works on both formats, Mac or PC. What we really came here for is Channel Mask. Just quickly before we get started, up until Photoshop released the Select Subject, and the Select & Mask function, all I did for kind of advance masking was Channel Mask, the thing we're going to do now. Because these two options that we learnt previously are so good, I don't use Channel Mask half as much anymore. 


Basically I use them for the same sort of principle. I need kind of like, say this kind of out of focus, what would normally be here, but this, these two here in combination are so much better now, in my opinion. The reason I still use Channel Mask, and the reason I still include it in this Advanced course, is because if we click 'Select' 'Subject', It tries to find a person's face, and there is no face to be found. So couldn't find subject, click 'OK'. So there's times where I just need to--


I want to select all this grass, but it's super hard, right? Quick Selection Tool is not going to do it. Magic wand's got no hope. I might do okay with a Color Range, but there are some perks to a Channel Mask, and you need it in your arsenal to be an advanced Photoshop user. You don't want to turn up at the Advanced Photoshop party, and not know what a Channel Mask is. Even though it's getting useless it's kind of those badges of honor, like, I think the Lens Flare was when you're new. 


So how does this work? I'm going to do it super quick, half to impress you, half to show you how quick it is once you know the-- once you get into the flow. Then I'll back it up and go a bit more step by step. So basically we go to the Channels Panel, we pick one of these three. The one that has the most contrast, blue does. So I'm going to right click it, duplicate it, click 'OK'. Turn this on, that off, then we use levels. And I'm just trying to accentuate the contrast, between the background and the foreground. I'm lifting this up, trying to find this kind of medium ground here. Let's click 'OK'.


I can blot in the stuff at the bottom here. I'm using my Paintbrush Tool, set to 'Normal'. I'm using black, making it nice and big. I'm just going to kind of paint it all out. Get a bit smaller and get some other stuff in there. Spend a little bit more time. I'm not, turn it into a selection. Go back into my Layers Panel and add a Layer Mask. First of all, reverse it out, invert the selection, add a Layer Mask. And you can see that will totally kind of freak you out, how fast it went there, but I guess I just want to show you the flow that I'm going through when I'm doing selections for something like this, and how easy it can be, because when I teach this live often people freak out, because there are quite a few steps. Don't worry, you won't probably remember them off by heart. I only remember them because I'm a trainer and I have to teach it all the time. 


When I wasn't, when I was just freelancing, I would go "Okay, Channel Masks, they're good." Come back to this video, and just run through it every time you need to do it. And that's just the way it is, there's a few steps involved, but the results are pretty cool. Let me grab this, and add it to the background here. You can see, a pretty convincing mask, with very little effort put in to getting it perfect. So let's back it right up. I'll show you a cool little trick, it's File Revert. Because we only have so many undos, right? So if you go to 'File', 'Revert', it goes all the way back to when the document was last saved. And in this case it's way back before I did all my channel madness. 


Let's look at it step by step and explain that a little bit. So it's channels that do the heavy lifting here. Basically a channel is just-- this document is RGB, you can see it up here in the tab. And that just means the computer makes all of these lovely colors out of a mixture of red, green, and blue. Now we're really not worried about channels at the moment, we're just going to use and abuse them to get our selection. What you're doing is you're looking through all three of these for the one that has the most contrast. In this case blue has a really clear contrast with the background. It's not always the case, sometimes it's red, sometimes green. So toggle through them all. Once you've found one you've got to duplicate it. Right-click it, 'Duplicate Channel'. I'm going to call it 'My Mask', for no reason. And I'm going to turn it on, and turn that one off. I don't want to destroy the red, green, and blue. I just want to work on this, my special little mask. 


We're going to delete it in a second. So with it selected, we're going to go to 'Levels'. So 'Image', 'Adjustment', 'Levels'. We're not going to use the fancy adjustment levels. We're going to use old school destroy the layer levels, these ones here. And all we're looking to do is, you can see the sky here, it's quite gray still, so I want to kind of increase the whites. Basically you can adjust these guys any way you like. All you need to do is have a really strong white versus black. So that's all I'm doing, drag them left them right to see, like if I go too far this way, it starts kind of bleeding in. There's a little bit of like, I've done it so many times, that I kind of got a good feeling. 


What you might have to do is get to this point, and say, "I'm going to try this, and then come back if it's not quite right." I'm going to crank the blacks up just a little bit as well. And I should point out-- I'm looking at the edge between this and this, I'm not worried about here, because, you saw it earlier on, it's blacked that in with a big paintbrush. It's this edge, this contrast between the background and the foreground here, that I want to, I guess get as sharp as I can. It feels okay. Click 'OK'. Now what I want to do is kind of fix this bottom stuff here, because I'm going to use my paintbrush. Set it to black. What kind of hardness? Somewhere in there, '80'. I'm just going to paint this in black. I'm going to do this to-- down the bottom here, quite rough, and then as I get closer I'm going to lower my brush, and get a little bit nicer about the whole experience, because I know that that is not a hole looking through. I know that's the sky, but I know this is just light that's reflecting on the grass. 


So I'm going to go in here and just kind of fix this up a little bit. We'll go through in-- after we do this exercise, I'll show you a few extra little tricks to tidy this up a little nicer. You saw the end result here, I put in less effort. And it came in still with a really good result. Channel Masks are awesome. So I got the basics in there. Now what I want to do is load it as a selection. You can click on this little icon down the bottom here. And it loads that black versus white as a selection. Now this guy here is--- his job is done. I click on 'RGB' to turn all of these on. Just make sure the eyeball is off on the mask, or you can bin it. Like we just don't need that anymore. People get a little caught up on that channel being part of it. Really we just used it to get our little matching ends here. 


Back to 'Layers', at the moment we have this sky selected. It really depends on your image. Sometimes you lever the right way around, sometimes you won't. If I click on 'Layer Mask' here, it's the opposite. So I'm going to go to select this. Now add my Layer Mask, and hey presto, you can see it was pretty bad along the top there, but it's still a pretty good mask. I'm going to grab my 'Move Tool'. I'm going to go 'Command C', 'Command V' on my Mac. Actually I probably do the other way around. I'm going to drag you, here. Use my little shortcut, 'Command-Shift-Square bracket'. 'Send to Back'. 'Ctrl-Shift-Square bracket' on a PC. You can see, a pretty convincing mask. 


Let's look at a couple of other things you can do with Channel Masks to get the most from them. Let's go to 'Channel Mask 3'. And I'll lie, we're not going to do Channel Mask 3 together, because it's very similar to this first one here. I'm going to set that as your homework in the next video. You can do it now onboards if you want. What I want to do is, let's go to 'Mask', 'Channel Mask 4' and '5'. These are the ones I'm going to combine. You saw them at the beginning. We run into the same problems, we can't use Select, Subject, but we're probably going to use a little bit of Select & Mask, just to kind of push this a little bit further. 


So same thing as before. Channels, I use these shortcuts here. If you're on a PC, is it Ctrl 3, 4, 5? Check whatever the shortcut is there. I'm holding down my 'Command' key and going 3, 4, 5. I'm not looking, just toggling through them all, just seeing. And don't worry about down here, you're looking at the transition between the sky and the background. And they're all really similar, actually because the background's pretty much white. I feel like, that's my one. You could argue on all the three of those ones. So I'm going to duplicate it. Duplicate, oh, don't delete it. Duplicate it. Can we give it a name? I'm not going to give it a name, because we're going to bin it in a second, so nobody's going to know we didn't name our layers. 


So 'Blue copy' selected, all the rest of them off. Otherwise you get this kind of weird colors going on. Make sure it's selected, and remember, we're going to go to our Levels, and we're just looking to increase this contrast, so I'm going to zoom in a bit, and I'm just looking at-- if we go too far you'll end up with this. It bleeds over the edge, and looks not very good. So I'm going to increase the white a little bit to get the sky pure white. I feel like that's a pretty good one. Looks like it's pretty strong black versus white. Click 'OK', zoom out, and I'm going to blot in the bottom here, using my Brush Tool, nice big brush. I'm going to add a little bit extra to this one, I promise. 


So we've got a selection, we're going to load it as a selection. We're going to click on 'RGB', you can leave that there. There's nothing wrong with leaving it there, click 'Channels'. 'Inverse' the selection, I'm using the shortcut 'Command-Shift-I' on a Mac, that's 'Ctrl-Shift-I' on a PC. And I've applied the Layer Mask. Now let's go and add it to our background. So actually going to bring this guy in, the other one, so 'Move Tool'. You come in here, friend. Want to know a cool extra little shortcut? You don't have a choice, I'm going to show you anyway. When you're dragging from one image to another, and you kind of like, ends up in a weird places, right? If you do that exact same technique. 


So 'Move Tool', drag drag, hold, hold, I'm holding the 'Shift' key. Then let go, and it doesn't put it willy-nilly, it puts it exactly kind of top left. Really handy, okay, moderately handy. And move it underneath. And you can see, it did a pretty good job, but because I've gone for such an extreme background, it's gone from light to dark, you can see, they're kind of ghosting around the edges. So I'll show you two ways of fixing this type of thing. One you've learned before, one you haven't. So I'm going to click on my 'Layer Mask'. Even though we started with a Channel Mask, we delved into the channels, and messed around in there, we can still click on the 'Mask' and go to 'Select & Mask'. I'm making sure mine's against on black. And you can play around with the radius, and in this case here, Shift Edge is probably going to work. It doesn't work great though, works kind of too far down into the image here.


So I'm going to hit 'Cancel'. What I want to do is show you a cool little trick. And it's to use your paintbrush, the B key. And just switch it from Normal to 'Overlay'. I'm going to make it an appropriate brush size. I'm going to make it kind of fuzzy there. Make a little bit bigger, and try and impress you. Look how good that is. I loved it when I found this option. Instead of trying to control it all with Select & Mask, you can just use your Brush Tool with Overlay, and just kind of tidy up the edges. It doesn't have to be a Channel Mask you've started with, can be with any mask. All it really does is gets rid of the kind of in between zones, so let's undo that and kind of have a look. If you hold down the 'Alt' key on a PC, or 'Option' key on a Mac, and click on the 'Mask', it just shows you in black and white, which is handy, right? 


I'm on 'Overlay', I'm on 'Brush Tool', black as my foreground color. And watch this, can you see, just like shrinks it in, or at least gets rid of the kind of gray areas. Can you see this white here in the middle, and there's black there, but there's this kind of like little bits of gray. And that's what the Overlay option is doing, as a brush. I'm going to zoom out. I'm going to turn. I'm going to hold down 'Option' key on a Mac, 'Alt' key on a PC. Go back in here, and just kind of fix that up. 


One thing I might want to do as well, is you can use that same key. I'm going to go back into here, you can see there's some like, you see, all this kind of gray area down here, you can do the opposite. Just flick it over to white. Make an appropriate Brush size, you can do some pretty kind of easy fixes. You can see, you can get quite close to the edge without wrecking it. If you're just using a white paint brush it can be a little tricky. We're trying to go fast. This tool is perfect for it. Tidy it all up. Jump back out, back in, looking pretty cool. 


So that's going to be it for Channel Mask, actually, one last bit. Let's use that same little tool, back here at the beginning, click on the 'Mask'. And we're going to use our 'Brush Tool', Overlay, I've set it to black now. And I'll lower the opacity just a little bit. If you've got the Brush Tool selected, the opacity, you can drag it down, that's fine. But cool little trick is just to tap '2' on your keyboard, '4', you can see it's changing up here, '6', '7'. I'm going to lower down to maybe 30%, and just kind of work these edges a little bit. There's a couple of fluffy bits that maybe aren't super realistic. And now we're actually finished. 


So that is a Channel Mask. Maybe bookmark this video. I know, when I was learning Channel Mask-- they're super cool, but really hard to remember what to do. It's quite process driven, there you go. Let's get on to the next video.

Written Guide

How do you create a channel mask in Photoshop?

Duplicate the colour channel with the strongest contrast between your subject and background, then use Levels and a brush to tidy it into a black-and-white mask. Load that channel as a selection, invert it if necessary, and add a layer mask. An Overlay brush can then help clean up grey, ghosted edges.

How to Mask Using Channels in Photoshop: Select Fine Detail and Clean Up Ghosting


Key takeaways

  • Select fine, out-of-focus grass using contrast already present in the image.

  • Choose the best RGB channel without damaging your original colour channels.

  • Turn a cleaned-up channel into an editable layer mask.

  • Reduce edge ghosting with a brush set to Overlay.

  • Use lower brush opacity for a gentler finish on soft edges.

The mighty channel mask deserves a place in your Photoshop selection toolkit. It has been around for ages, and although I use it less now that Select Subject and Select and Mask are so useful, it still earns its keep on awkward images.

Think of a field of grass with hundreds of fine tips, some sharply focused and others lovely and blurry. Quick Selection is going to struggle. The Magic Wand is hardly going to save the day. Colour Range might do a reasonable job, but a channel mask gives you another way to separate that detail from the sky.

And even if you already know the channel-mask routine, there is a particularly handy brush trick worth keeping: painting on a mask in Overlay mode to tidy up those ghosted edges. That trick works on other layer masks too.


When a channel mask is worth using

Channel masking uses the difference in brightness between your subject and its background. Rather than asking Photoshop to recognise an object, you find a colour channel that already separates the two reasonably well and strengthen that separation.

In the grass example, Select Subject cannot identify a subject successfully. That does not mean channel masks should replace the newer selection tools. I often prefer those tools when they work well. It simply means that when automatic selection lets you down, channels are another option.

The examples here use grass against a pale sky, followed by a forest against a nearly white sky. Both have complicated edges but useful foreground-to-background contrast. That is the combination we are looking for.


Set up your images

Open your foreground photograph and the background you want to place behind it. If you are working with the accompanying exercise files, these are the Channel Mask images numbered 01 through 05 in the selections and masking folder.

A quick housekeeping shortcut: Control + Tab cycles through open document tabs on both Mac and PC. It is handy when you have several foreground and background images open.

The whole channel-mask process follows this pattern:

  1. Compare the Red, Green and Blue channels.

  2. Duplicate the channel with the strongest edge contrast.

  3. Use Levels to strengthen the black-and-white separation.

  4. Paint in the solid areas.

  5. Load the channel as a selection.

  6. Return to RGB and the Layers panel.

  7. Invert the selection if necessary, then add a layer mask.

  8. Check it against the replacement background and refine it.

There are a few steps, but none is especially complicated. Do not worry if you cannot remember the whole sequence straight away. I remember it because I teach it repeatedly. When I was freelancing, this was exactly the sort of process I kept a reference for.


Create a channel mask for out-of-focus grass

1. Find the channel with the best contrast

Open the Channels panel. An RGB image contains Red, Green and Blue channels, which Photoshop combines to produce the full-colour image. Clicking an individual channel displays its information in greyscale.

Click through all three and compare the boundary between the grass and the sky. In this example, the Blue channel gives the clearest separation: the sky is light and the grass is dark.

Blue is not always the winner. Another image might work better with Red or Green. Look at the actual edge you need to select, not just which channel looks most dramatic overall.

Adobe Photoshop interface showing a black-and-white view of tall wheat stalks, with the Blue channel highlighted in the Channels panel on the right.

The useful channel is the one that separates the fine grass tips from the sky.

2. Duplicate it before making changes

Right-click your chosen channel and select Duplicate Channel. You can call the copy “My Mask” if that helps you keep track of it.

Select the duplicate and make it the only visible channel. Leave the original Red, Green and Blue channels alone. We want a working copy to build our selection, not an accidental colour adjustment to the photograph.

If the image develops odd colours or a coloured overlay, check the visibility icons. For this stage, you want to see just the duplicated channel in black and white.


3. Strengthen the contrast with Levels

With the duplicate selected, choose Image > Adjustments > Levels. This is a direct adjustment to the copied channel, not a Levels adjustment layer.

Adjust the sliders to make the sky white and the grass darker. The exact settings depend on the image, so there is no magic number to copy.

Zoom in and concentrate on the grass-to-sky boundary. Push the white and black points far enough to improve separation, but not so far that the edges bleed, expand or lose useful detail.

Photoshop workspace with a Levels adjustment dialog open over a high-contrast black-and-white silhouette of grass blades, adjusting input shadow, midtone, and highlight sliders.

Use Levels to strengthen separation while keeping an eye on the delicate edge detail.

Do not spend ages trying to make the entire lower half perfect with Levels. We can paint that solid area in a moment. The edge is where the channel needs to do the heavy lifting.

There is a little trial and error involved. Try a sensible setting, check the resulting mask against your new background, and come back if it needs another pass.


4. Paint the solid foreground black

Choose the Brush Tool, set its mode to Normal, and make black your foreground colour. A fairly firm brush, around 80% hardness in this example, works for filling the solid lower section.

Start with a large brush and paint across the bottom of the grass. Reduce the brush size as you get closer to the intricate upper edge.

The distinction here matters: some pale areas are genuine sky showing between blades, while others are simply light reflecting off the grass. Keep the real gaps, but paint over highlights inside areas that should remain solid foreground.

You can be fairly rough well away from the edge. Near the grass tips, slow down and use a smaller brush.


5. Load the channel as a selection

Click the Load channel as selection icon at the bottom of the Channels panel. Photoshop uses the channel’s brightness values to create the selection.

Now click RGB to restore the full-colour display. Turn off the duplicate channel’s visibility.

You can keep the duplicate for later or delete it once you no longer need it. It has done its job: it supplied the selection. It does not have to remain as part of the finished layer-mask setup.


6. Invert if necessary and add the layer mask

Return to the Layers panel and select your foreground layer.

In this example, the white sky was selected, but we want to keep the grass. Choose Select > Inverse, then click Add Layer Mask.

The inverse-selection shortcut is:

  • Mac: Command + Shift + I

  • PC: Control + Shift + I

Not every image needs that inversion. If your subject was the light part of the channel, the selection may already be the right way round. Check which part you are keeping before adding the mask.


7. Place the replacement sky underneath

Use the Move Tool to bring your replacement sky into the foreground document, then move its layer beneath the masked grass.

The shortcut for sending the selected layer to the back is Command + Shift + [ on Mac or Control + Shift + [ on PC.

Full-color image in Photoshop showing vibrant green wheat blades cleanly masked in front of a blue sky with fluffy white clouds, with the layer mask visible in the Layers panel.

A channel-based selection can preserve a convincing soft grass edge with surprisingly little manual work.

That is the basic channel mask. A complicated edge, a few straightforward operations, and a pretty convincing result.

If you want to restart an experiment, File > Revert returns the document to its last saved state. Unlike stepping backwards through a limited undo history, it takes you straight back to that saved version, so make sure you are happy to discard the changes made since then.


Repeat the process on trees against a pale sky

A forest skyline uses exactly the same approach. Compare the channels, duplicate the best one, increase the contrast with Levels, paint the lower forest solid black, and load the result as a selection.

In this example, the sky is nearly white already, so all three channels offer fairly similar contrast. Pick the one that gives you the most useful transition around the treetops. Do not worry about detail deep inside the forest when choosing it.

Again, avoid forcing Levels too far. Get the sky cleanly white without making the tree edges look unnatural, then fill the solid lower section with your Normal-mode black brush.

Restore RGB, return to Layers, invert the selection and add the layer mask. Bring in the darker replacement background and place it underneath.

When dragging between documents, holding Shift as you release the mouse helps place the incoming image consistently rather than dropping it wherever your pointer happens to be. Check the position afterwards and adjust as needed.

The grass-on-white exercise image is also a useful practice subject. Run through the same sequence yourself: the goal is to get comfortable choosing contrast and judging the edge, rather than memorising a particular set of slider positions.


Fix ghosting around the mask edges

The forest mask looks fairly good initially, but replacing a very light sky with a very dark background makes pale ghosting around the treetops much easier to spot.

There are two useful ways to tackle it.


Try Select and Mask first

Click the layer-mask thumbnail and open Select and Mask. A mask created from channels is still an ordinary layer mask, so you can refine it with the same tools you would use on any other mask.

Set the preview to On Black to inspect the pale edge. Try Radius and Shift Edge to see whether they improve the result.

In the forest example, Shift Edge helps a little, but pushing it far enough to remove the ghosting also cuts too far into the trees. If that happens, cancel rather than accepting a damaged edge.


Use the Brush Tool in Overlay mode

Here is the lovely little trick. Select the layer-mask thumbnail, press B for the Brush Tool, and change the brush mode from Normal to Overlay.

  1. Set black as the foreground colour.

  2. Choose a soft brush sized for the area you are cleaning.

  3. Paint gently across the ghosted edge.

  4. Inspect the result and build up the effect where necessary.

On a black-and-white mask, an Overlay brush lets you work on the grey transition while protecting the pure black and pure white areas. Painting with black darkens the intermediate mask values, helping hide the unwanted fringe.

Instead of trying to control the entire boundary with a global setting, you can brush over the particular sections that need attention. Handy, right?


Inspect the mask directly

Hold Option on Mac or Alt on PC and click the layer-mask thumbnail. Photoshop displays the mask itself in black and white.

Close-up black-and-white view of tree branches in Photoshop, showing a large circular brush cursor painting over foliage edges to refine the black-and-white alpha mask.

Viewing the mask directly makes the grey transition and unwanted internal gaps easier to find.

White reveals the layer, black hides it, and grey reveals it partially. In this view, you can see exactly which intermediate areas the Overlay brush is changing.

Use the same Option-click or Alt-click action to return to the composite. Switch between the mask and the finished image as you work.


Paint with white to restore solid areas

You can use the same technique in reverse. Switch your foreground colour to white and paint over grey areas inside the forest that should be fully visible.

That strengthens the mask’s lighter values and helps tidy unwanted partial transparency within the subject. It is easier to get close to an intricate boundary than it would be with a plain white brush in Normal mode.

This is not exclusive to channel masks. The Overlay-brush technique can help refine any layer mask with grey areas that need strengthening towards black or white.


Use lower opacity for a gentler finish

Back on the grass composite, a full-strength brush might be more than those soft tips need. Select the mask, keep the brush in Overlay mode, choose black, and reduce the opacity to around 30%.

Work gently over any fluffy edge areas that feel less convincing. Lower opacity gives you a more gradual adjustment instead of making a large change in one stroke.

With the Brush Tool active, number keys provide a quick opacity shortcut:

  • 2: 20%

  • 3: 30%

  • 4: 40%

  • 6: 60%

The important thing is not to remove every soft transition. Out-of-focus grass should still look out of focus. Clean up the unwanted fringe without turning a naturally blurred edge into a hard cut-out.

Keep the process simple: find contrast, duplicate, strengthen, paint, load, invert if needed, and mask. Then judge the result against its actual background. The channel gets you most of the way there; the Overlay brush gives you a quick, local way to finish.


Key terms

RGB channels

The Red, Green and Blue components that combine to form a colour image. Viewed individually in greyscale, they can reveal useful contrast between a subject and its background.

Channel mask

A masking technique that uses a copied colour channel as the starting point for a selection. Levels and painting strengthen the separation before the selection becomes a layer mask.

Layer mask

A greyscale mask controlling a layer’s visibility. White reveals, black hides, and grey creates partial visibility.

Ghosting

An unwanted fringe around a masked edge, especially noticeable when a pale original background is replaced with a dark one.

Overlay brush mode

A brush blending mode useful for strengthening grey values on a mask towards black or white while protecting areas that are already pure black or pure white.


FAQs

Which channel should I use for a Photoshop channel mask?

Use the channel with the strongest useful contrast at the boundary between your subject and background. Compare Red, Green and Blue for each image rather than assuming Blue will always work best.

Why does my mask keep the sky instead of the foreground?

Loading a channel as a selection selects its light areas most strongly. If your sky is white and your foreground is black, invert the selection before adding the layer mask.

Do I need to keep the duplicated channel?

No. Once it has supplied the selection, you can delete it. You can also keep it for later use, provided its visibility is turned off when you return to the RGB image.

Can I use Select and Mask after creating a channel mask?

Yes. Select the resulting layer-mask thumbnail and open Select and Mask. If adjustments such as Shift Edge remove too much subject detail, try local refinement with an Overlay-mode brush instead.

How can I clean up a mask without making soft edges too harsh?

Use a soft Overlay brush at reduced opacity, around 30% in the grass example, and build up the adjustment gradually. Check the composite regularly so you preserve natural blur while reducing unwanted ghosting.

Daniel Walter Scott

Written by Daniel Walter Scott — Founder of Bring Your Own Laptop & Chief Instructor

  • Powered by Marvin
  • Terms of use
  • Privacy policy
  • Cookie policy
  • © Bring your Own Laptop Ltd 2026
🎬 After Effects Essentials is Now LIVE!

🎬 After Effects Essentials is Now LIVE!

Kyle Hamrick’s brand-new After Effects Essentials course has officially launched!

Jump in and start bringing your ideas to life with motion, animation, and visual effects, all taught step-by-step from the ground up. 🚀

Whether you’re completely new to After Effects or ready to build your confidence, there’s plenty to explore, create, and animate.