A pixel in the sensor of a DSLR camera really only counts the number of photons that strike it. This number corresponds to the brightness of that part of the image represented by that pixel. Individual pixels don't really see in color.

Color in an image is created by combining information shot through red, green and blue filters over individual pixels in the sensor of a DSLR camera.

By combining these three colors, we can produce all of the colors in the visual spectrum.

Every color image is made up of three parts or channels, one each for red, green, and blue information. These channels represent the original brightness information that the pixels recorded. These channels are grayscale, but they represent color information because of the filters. The red, green and blue channels are combined into what is called an RGB color image.

Sometimes one of these three channels in a color image will be sharper than the others. Frequently, the seeing is better for long wavelengths on the red end of the spectrum. However, the Bayer array in a DSLR camera has twice as many green pixels, so it can often be the sharpest channel.

The reason this is useful is that some subjects, like the Moon, and Sun, actually have very little color in them. We can sometimes pull out the sharpest channel out of a color image to produce a black and white image that is sharper than the color image.

In other specialized forms of planetary imaging, such as narrowband hydrogen-alpha solar photography, an image may have data in only one of the channels. In this example of a hydrogen-alpha image, there really is data only in the red channel. Figure 1 shows a color image shot through a special narrowband solar hydrogen-alpha filter.

Let's take a look at the individual red, green and blue channels in this image.

Red Channel            Green Channel            Blue Channel

Figure 1 - Narrowband hydrogen-alpha image of a solar flare associated with active region 1520 on the Sun. Hold your mouse cursor over the image to see the red channel. Hold your mouse cursor over the text descriptions of the channels under the image to see each individual color channel. Virtually no data was recorded in the green or blue channels.

In the mouse-over examples above, we can see that there is data only in the red channel. Let's take this channel out of the image and use it to make a better picture than the color image.

Figure 2 - The Channels Palette

• Open the Channels palette and click on an individual channel and examine it.

• Go to Windows > Channels to activate the Channels Palette (Figure 2).

• Click on the red channel to make it active. The color image should change to black and white.

• Under the pull-down menus at the top, go to Select > All.

• Under the pull-down menus at the top, go to Edit > Copy.

• Under the pull-down menus at the top, go to File > New.

• Under the pull-down menus at the top, go to Edit > Paste.

• Under the pull-down menus at the top, go to Layer > Flatten Image.

• Save the file with a new name.

Let's adjust the contrast and apply some sharpening, as described in the previous sections.

Hold your mouse cursor over the image to see a comparison between the original red channel and the red channel after the image's contrast was increased and it was sharpened.