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Most techniques for converting an image to black and white, involve blending individual Color Channels at varying percentages, but across the whole image. However, through the use of layer masks, you can actually create an image that blends different channels through different areas of the photo. In this lesson, I'll show you how it's done. This technique utilizes the individual color channels found in the image. So first, let's go to the Channels panel. You can choose Window > Channels from the menu if it's not visible, and then we'll click on the thumbnails of each of the individual color channels in turn. Starting with red, then green, and then blue.
As you can see, because different areas of the image contain different percentages of each of these primary colors, each of the channels looks quite a bit different. The red and the green channels, in this case, are relatively similar to each other, but there are some differences and the blue channel looks dramatically different. I think I'm going to use the blue channel as the basis of my final black and white image, and of course, I'll blend in Elements of the green and the red channels as well. I'll click on the RGB Thumbnail to get back to my color image, and then I'll click on the panel pop-up menu at the top-right of the Channels panel, and I'll choose Split Channels from the pop-up menu.
This will split my image into three separate images. Each of these is a grayscale image representing one of the original channels. You can see the names of the images now reflect the R for red, G for green, and B for blue. So these are each of my individual channels. I'll switch my view, so that I can view all three of these images at once, and then I'll choose the Move tool from the toolbox holding the Shift key so the image will be centered. I'll drag my green channel into the blue channel. I'll then go to my red channel, and drag it, again, holding the Shift key, and drop it on the blue channel as well. At this point, I can close my green and my red channel and I don't need to save either of those.
I'll go back to my Layers panel, and as you can see, I have a background image layer, a Layer 1 and a Layer 2. These represent the various channels within the image. Now I want to use a layer mask, so that I can only see the background image layer, but then, I can paint in certain elements from Layer 1 or Layer 2. So I'll click on the thumbnail for Layer 2, and then hold the Alt key on Windows or the Option key on Macintosh, while clicking on the Add Layer Mask button, the circle inside of a square icon at the bottom of the Layers panel. By holding Alt or Option while clicking this button, the layer mask will be filled with black by default.
That means that this layer is hidden, because black blocks and white reveals. I'll then click on Layer 1 and do the exact same thing, holding the Alt Or option key while clicking on the Add Layer Mask button. Now, I've blocked both Layer 1 and Layer 2, so all I'm seeing is the background image layer. If I want to take a look at one of these other channels, I can temporarily disable the Layer Mask. For example, I'll hold the Shift key and click on layer 2, and then Shift+Click once again, and the same thing with Layer 1.
This allows me to temporarily view that particular layer, because I'm no longer blocking it. As you can see, this layer has a good sky, and actually, the mountain looks better here, too. So I'd like to use this layer in conjunction with my original background image layer, the blue channel in this case. So click on the Layer Mask, for Layer 2, I'll choose the Brush tool from the tool box, and then press the letter D on the keyboard to set the default colors. When working with a Layer Mask, those defaults are white for the foreground and black for the background. I'll then make sure that I'm using a brush with a 0% hardness, so I have a nice, gradual transition for the painting I'm about to do. Then I can paint directly on the image.
What I'm really painting on, is the layer mask, which means I'll be blocking or revealing specific areas of the image. Using the left square bracket to reduce the size of the brush or the right square bracket to increase the size of the brush, I can finetune the size of my brush and then start painting. When I paint on the image with white, I'm actually affecting the layer mask, and so, I'm revealing this portion of the current image layer. In other words, I'm blending portions from various channels. I've used my blue channel as the underlying basis of the image, but then, I'm painting in areas from the other channels.
I think I'd also like to reveal a little bit more detail for the flowers. I've disabled the layer mask for Layer 1 and it looks like that might be a better choice for my flowers. However, I don't want to bring that in at full strength. So now, I'm going to paint with white, but I'll do so at a 50% opacity. So I'll set my opacity down to about 50%, and now, when I paint, I'm only adding half of this layer to my underlying image layer. In this case, that will give me just a little bit of detail without losing that nice bright effect in the flowers. In fact, I think it works pretty well for the foliage and I might even brighten up the trees just a little bit as well.
I can continue working with any of my layers here, painting with black to block a particular area or white to reveal the area. And I can work at a reduced opacity as needed if I want to partially reveal a particular area. Blending channels through the use of Layer Masks affords you much more flexibility compared to simply blending those channels based on their relative contribution to luminosity values. There's no question this involves a fair amount of work. But for some photos, that extra work can result in a huge pay off.
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