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Photoshop CS4's adjustment features offer unparalleled opportunities to correct and manipulate images. In Photoshop CS4: Image Adjustments in Depth, Jan Kabili explains how to use all the major Photoshop adjustment features. She shares the best techniques for adjusting image quality, and shows how to use the new Adjustments panel to streamline a photo correction workflow. Jan also demonstrates multiple ways to eliminate color casts, and explains how to use the new On-Image Curves control to adjust brightness and color. This course offers a detailed look at the techniques photographers and designers use to master image adjustments in Photoshop. Exercise files accompany the course.
Another way to convert a color image to black and white is to use the Channel Mixer adjustment. That can be applied as a direct adjustment from the Image menu or as an adjustment layer. So I'm going to add a Channel Mixer adjustment layer to this color photograph by clicking here on the Channel Mixer icon in the Adjustments panel. That changes the controls here in the Adjustments panel to those for the Channel Mixer and interestingly, the default controls are not setup to convert from color to black and white but rather to mix a custom Color Channel. In this case, a custom Red Channel made up of values from the Red, Green and Blue channels in the image.
That's not what I'm going to show you in this movie. Instead, I want to concentrate on how you can use the channel mixer to convert this image from color to black and white and the secret is to click this check box right here that says Monochrome. As soon as I click that, Photoshop gives me a default black and white conversion in the document window and it changes the output channel to gray. What I'm going to be doing in this panel is mixing or creating a new distribution of brightness values from the three gray scale channels; red, green and blue that make up an RGB image.
Before I start making that special recipe, I usually take a look at each channel to see which parts of a particular channel are bright and which are dark. To do that, I'm going to go to the Layers panel, I'm going to make the Channel Mixer adjustment layer temporarily invisible by clicking its Eye icon and then I'm going to click on the Image layer, the Background layer. Then will go to my Channels panel here and if yours isn't opened, you can open it from the Window menu at the top of the screen. In an earlier movie, I showed you that an RGB color image is made up of three gray scale channels; each of which contains different versions of brightness values. So I'm going to click on the Red channel and I can see that here the man and his shirt are quite light and the rest of the image is darker.
If I click on the Green channel, I see that there is lots of detail in the background and in the water but the man is much darker. And if I click on the Blue channel, the water is light but the man is dark and there is not as much as detail in the forest as there was in the green. I also see some noise in the dark areas in the Blue channel. So I'm probably not going to want to use too much of the Blue channel. I am going to click back on the RGB Composite channel to make the image appear colored again and then I'll go back to the Layers panel. I'm going to make the Channel Mixer layer visible again by clicking in its Eye icon space and then I'm going to select the Channel Mixer layer to bring up the channel mixer slider again in the Adjustments panel.
So what I just learned from looking at the channels is that if I want a lot of detail in the background and in the water, I might want to increase the amount of green in my gray scale mix. Before I do that, take a look at the default values. By default the channel mixer uses a mix of brightness values that's 40% from the Red channel, 40% from the Green channel and 20% from the Blue channel. That doesn't sound too bad in this case because I did notice that there wasn't too much l liked about the Blue Channel. I really liked the Green channel and there were some things I liked about the Red Channel.
I actually would like to lighten the man's face to focus attention there. So I do want to go to the Red slider here and increase that percentage. I could just click-and-drag on this gray slider like this but that's a little bit difficult to control. So I'll put that back approximately where it was and instead, I'm going to click in the Red field and I'm going to use the Up arrow on my keyboard to move up one percentage point at a time and if I go so far that I don't like the result, for example, here I see that the man's hand is starting to blow out, I'll back off by clicking the Down arrow key on my keyboard.
So maybe I'll put this at say 50. Now if you take a look at the total, you will notice that it's more than 100 and I get this little warning sign telling me that. For creative purposes there is nothing wrong with having the total of all these percentages add up to more than 100. The danger of doing that is that I might lose detail in the highlights. At 100%, I'm just maintaining the correct distribution of brightness or tonal values in the image. But when I go above that, I'm going to be pushing some white values to pure white and I can see that if I look at the Histogram panel, which is up here, there is a small spike starting to grow on the right and that's because I do have a Total brightness value of more than 110.
So to even that out, I might want to go into my Blue channel by clicking in the blue field and then press the Down arrow key on my keyboard to reduce the percentage from the Blue Channel and get things back to 100%. Now let's say I want to add some green because I want to open up the forest and I noticed that in the Green Channel, I had some lighter values back here. I'll click in the Green Channel field, and I'll press the Up arrow. By the way, if you hold the Shift key and press the Up or Down arrows, these numbers will move in increments of 10%. So I'm going to Shift-click the Up arrow and that does open up the forest. I'm going to try that one more time. So I like the look in the background but now again, I'm way past 100%, I have that spike growing in the Histogram and I have blown out a bunch of highlights here in the image.
So I'm going back to the Blue channel and I'm going to reduce it even further. Maybe I'll take that all the way down to something like 5% and I'll go to the Red channel and I'll reduce that and I'm still a little bit over 100%, so I'm going to back off a little more on the greens taking that down to 55. So as you can see the process of working in the Channel Mixer is a back and forth amongst the three Red, Green, and Blue sliders trying to get just the right mix of brightness values from each of the gray scale channels. If you take the time and you have the patience to work with the Channel Mixer, you can get some really great results and exercise lots of control over those results.
But to be honest, in most cases, I find it easier to work in the Black & White adjustment layer where I don't have to worry as much about these numerical values or trading off between various sliders. But when you are working on a professional job or really special image, you might want to give the Channel Mixer adjustment layer a try.
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