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A color photo in the RGB color mode consists of three individual color channels: red, green, and blue. Of course, the reality is that these color channels actually don't contain color information per se, rather they are each a gray scale image that represents the amount of each color that should be included for each pixel in order to produce the final color image. By understanding the information contained in the color channels for a given image, you can greatly improve your ability to produce the best black and white image possible. Let's take a look at these channels.
If the channels panel is not already available to you, you can simply choose window, channels, to bring it up. We'll have an RGB tile at the top of our channels panel, which represents the composite of the individual channels contained within the image. You can view the channels individually by simply clicking on the thumbnail for that channel. For example, we'll start with the red channel. The red channel, as you can see, doesn't really contain red information exactly. It contains black and white information. But that black and white information represents the relative luminence of red within the image.
In other words, we can look at a particular pixel and determine, relatively speaking, how much red is contained in that pixel. If we look up in the sky, which is mostly blue and cyan, you'll see that the red is dark in most areas. That means there's very little red in the areas of the image that appear blue, and that makes perfect sense. There is some red in the petals of the poppy and since the the poppy is orange, and red is very close to orange, it makes sense that there would be some red light contained within the poppy. Of course it might seem confusing then that we have what appears to be a fair amount of red in portions of the sky.
But looking back at the color image, you can see that that's where the image appears white because of the clouds in the sky. And of course white light represents a maximum or nearly maximum degree of all 3 colors of light, red, green and blue blended together. Of course in the real world there are more than just three colors of light, or what we have done is separated light into several ranges of colors and we have given those names red, green and blue and when we mix all of the colors together we get white. So, white areas of the image you would expect to see is relatively bright on all of the channels.
Of course beyond just reading the channel to get a better sense of which color appears in a various areas, hopefully you can get a sense that this represents some information we might use in a black and white version of the image. The red channel is going to show most contrast when there's a difference between relatively red and relatively non-red or more green and blue areas of the image. So for example, for a portrait, typically the red channel will be fairly contrasty. Let's move on to the green channel. You might be aware that most digital cameras use an imaging sensor where there are twice as many green pixels as there are red pixels or blue pixels.
That's because the green range of color values are those that are most readily present in the natural world. As a result, more often than not, you'll find that the green channel represents the best starting point for a black and white photo. That's because it will usually contain the maximum amount of detail, texture, and other information that is useful in that final image. Next we'll take a look at the blue channel. And as you can see here, it's a very contrasty channel. That's of course because we have a blue sky, and so those areas of the image appear nearly white. And we also have an orange poppy.
Well, orange is very, very close to yellow, and yellow of course is the opposite of blue. And the poppy, which contains a fair amount of yellow, looks nearly black in this particular channel. The blue channel is the one you're least likely to use in most situations. It is usually the channel that contains the most noise and other problematic artifacts within the image. Of'course it can be very helpful, and in many situations will provide a good degree of contrast for certain areas of the image. The key is to be aware that there are differences among these channels and that we can use all of them in taking our original color image and converting it to black and white.
When it comes to producing a great black and white image, I can stress enough how important it is to have a slid understanding of what channels are and what information they contain. Channels are at the heart of most techniques for creating a black and white image from a color original. So when you understand color channels, you'll have a much greater understanding of black and white.
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