Learn about duplicating Alpha Channel in this Adobe CS3 Print Workflow training video series.
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So if this gives you an idea where you are headed that's really helpful. What we want when we finish our mask is a the dandelion shaped hole in a black background. And this is not going to be as hard as it sounds because we are going to let Photoshop help us out. We are going to use our channels as a guide. We are going to pick one channel that gives us a good head start, we are going to duplicated it and then we are going to make the mask from that. So let's shop through the channels and see which one comes the closest to giving us a white dandelion shaped hole in a black background.
Let's click on the name Red, not bad. Click on the name Green, click on the name Blue. If we look back through, I think you will agree that the Red channel gives us the best start. I know it's not solid black in the background, and the dandelion is not white but we have got enough contrast between the dandelion and the background to give us a shot.
So to duplicate the channel, go to the drop down menu of the Channels panel, choose Duplicate Channel. We can give it a fancy name like dandelion mask or we could just leave it as the default. I think it will be helpful if we leave it as Red copy so we sort of remember where we have got this, click OK and at first it looks like nothing has happened but if you look up in your Title bar, you will see that you Title bar tells you, you are in the Red copy channel, you look over in the Channels panel and you see that Red copy is selected.
Click on the eyeball by Red copy, turn off the eyeball by Red, you may or may not have to do that but our goal here is to just be looking at the Red copy channel as a starting point and have no other channels selected. Now what we have to do is manipulate the pixels in this channel so that we have a black background and a white dandelion shaped hole. I am going to suggest that we use Levels. Go up to Image>Adjustments>Levels or you can hit Ctrl+L on Windows, Command+L on the Mac and grab it by the Title bar and move it out of the way so you can see what's happening.
Grab that little black triangle underneath the histogram, that sort of land mask that you see on the window and drag to the right just to get a feel for what's going to happen. You can see as you drag that little guy further to the right, that background begins to darken. When you are creating a density mask, which is what we are doing and you are using levels to make this kind of change, you are going to find you sort of have to noodle back and forth between the extreme ends. You have to pull the little black slider end to see how it's doing. Come back with the white slider a little bit, you sort of juggle those end points, the lightest areas and darkest areas against each other. You can also use the little middle slider which governs midtone levels and it looks like that did a pretty good job moving them over.
We don't want to come in too far with that black pull because we are going to erode some of the content, we want to maintain all those little translucent tendrils of this dandelion head. You may never have to silhouette a dandelion every in your life but I bet you are going to have circumstances where you need to silhouette people with soft hair or animals' fur or leaves on trees and principle that we are applying here is going to help you with all of those.
So your goal, again, is to have pretty good representation of the dandelion. Now you are going to have to do some hand work in almost every circumstance and if this had been shot on a flat background, we be completely out of luck. So you are going to have your best results, you will yourself less crazy if you use subjects that are shot on fairly uniform background the contrast with the subject itself.
So let's see how far we have gotten. I am going to click OK. We are going to use the Info panel to find out how well we are doing. When you click on the tab for the Info panel, then move your cursor over and do a reconnaissance run around. If you look in the upper left hand quadrant of the Info panel, you will see just the letter K meaning black and you will see a value. I got ahead a nice solid background but apparently I don't. Here is a way that you can check too. You can invert this image so that you can see a negative version of it. Sometimes that makes it easier to see where the mess is. If you go up to Image>Adjustments and Invert or you can hit Ctrl+I on Windows, Command+I on the Mac. Now you can probably see some of the dirt back here in background.
I could give it another pass with levels or I can paint with my brush. So sometimes painting with the brush is a little bit easier. Let's choose the Brush tool, make sure that white is your foreground color because that's the color that you use when you use any of the painting or drawing tools. But when you come in, you may find that you have a little bit of brush like I do. So let me show you a great way to change the size of your brush without a trip up to the Brushes palette. If you look down at your keyboard, next to the P, you will see left bracket, right bracket. You don't need a Shift key, all you need to do is press the left bracket to make your brush size smaller, the right bracket to make it larger. Since I need a bigger brush, I am going to tap my right bracket and you will see with tap the brush size gets bigger and bigger. If you are in a hurry, you can just hold down that bracket and it will go in big jumps. I think I probably went too far.
Now remember the color you are going to paint with your Brush tool is going to be your foreground color. So make sure that your foreground color is white before you begin painting. An easy way to ensure that your background and foreground colors are the default, is to press D the for default key on your keyboard and if you keep an eye on your foreground and background color indicators at the bottom of the tools panel watch what happens when you hit the X key on your keyboard. It swaps them, it swaps your foreground and background colors. And when you start creating masks like this, it's really helpful to not have to take trips over the Tool panel to change these things or to swap them, you can just hit that X to swap and then you are good to go.
So I want to paint with white, I am going to paint around here and get rid of all that scum that's in the background. I am going to go close to my dandelion but not too close because this is a soft edge brush and I could mess it up. So our goal here, remember, is to have a white dandelion shaped hole in a black background. We are backwards now because we inverted this to take a good look at it.
Let's invert it again. Go to Image>Adjustments>Invert. Now it looks like I may have caught my stem with my brush when I was painting the background but I can fix that. I am going to get my Lasso tool, I am going to draw just a sloppy little selection around here and I am going to use Levels to open up that area; to opening up meaning to lighten up. I am going to go to Image>Adjustments>Levels and I am going to pull on that little white slider. There I think that I cleaned it up. I am going to click OK and good habit I am going to deselect, Select and Deselect. But sometimes you can't get everything you need by using Levels or Curves. Often you have to do a lot of hand work like we did in the background.
There is a little problem with the sort of hole at the middle of this dandelion. I am going to get my Zoom too, I am going to click-and-drag and create a zoom marquee so I can concentrate on the head of the dandelion where I need to do a little bit of tunning up. I think you can see there some ambiguous areas where it's gray, if I leave it the way it is, there are going to be parts of the interiors of this dandelion that are going to show in the finished image. So I need to make sure that I have a good white shape here for the heart of the dandelion.
If I am not sure where the dandelion stops and the background begins, I can trace the color. I can go over to the Channels palette., click on the eyeball by RGB, not the name but the eyeball, and now I can see that yes this is definitely part of the dandelion and I want to make sure I k