Separating Images by Channels

We can separate RGB images into three grayscale images that contain the color values for each R, G, and B channel by saving each channel as a mask. We can separate RGBa images into four grayscale images for each R, G, B and alpha channel. To do so, we use the Edit - Save Mask/Channel dialog. See the Masks topic for detailed discussion on masks.

Separating an RGB Image into Separate, Per-Channel Grayscale Images

1. Open the RGB image to be separated.

2. Use Edit - Save Mask/Channel to save the red channel into a grayscale image.

3. Use Edit - Save Mask/Channel to save the green channel into a grayscale image.

4. Use Edit - Save Mask/Channel to save the blue channel into a grayscale image.

Example

$images\img_bronze.gif$

We can use the Layers pane to see the separate R, G and B channels in an image. We can save each of these channels using Edit - Save Mask/Channel to save the channel as a gray scale image.

$images\img_bronze_r_channel.gif$ $images\img_bronze_r_grayscale.gif$

The image on the left shows the red channel. The image on the right shows the grayscale image created as a mask from the red channel. Note that the sky is dark in the grayscale image because pixels in the blue sky have low values in their red channel.

$images\dlg_save_mask_channel.gif$

We can create the image on the right from the red channel of the bronze image by choosing Channel: red in the Save: box of the Edit - Save Mask/Channel dialog.

$images\img_bronze_g_channel.gif$ $images\img_bronze_g_grayscale.gif$

Likewise, we can create a grayscale image for the green channel. Note that the bronze monument has bright tones in it because of the green color of the bronze monument.

$images\img_bronze_b_channel.gif$ $images\img_bronze_b_grayscale.gif$

Finally, we can create a grayscale image for the blue channel. Note how the sky is the lightest in this grayscale image because of the large amount of blue in it.

We can apply editing effects to the separate images and then recombine them back into an RGB image using the Edit - Load Mask/Channel dialog. See the Combining Channels into Images topic for an example.

Note that we do not need to split up an RGB image into separate grayscale images just to apply effects on a per-channel basis. Editing commands apply only to those channels that are visible. If we wish to apply commands to only one channel at a time we can uncheck the other two channels in the Layers pane and they will remain unaffected.