An image consists of three color channels, namely RED, GREEN, and BLUE. Together these channels form an RGB image into independent grayscale images that can be saved as separate files. In the example, the original color image “VTP_2759.jpg” is shown. It is then split to three grayscale images: “VTP_2759_R.jpg” (RED), “VTP_2759_G.jpg” (GREEN), and “VTP_2759_B.jpg” (BLUE).
The original image “VTP_2759.jpg” (Photo by Vicente Tabora Photography, Model Jourdan Miller)
Split channel images (from L to R): “VTP_2759_R.jpg” (RED), “VTP_2759_G.jpg” (GREEN), and “VTP_2759_B.jpg” (BLUE)
They can be saved to storage separately as greyscale black and white images and adjusted depending on how the retoucher wants it to look. With advanced techniques that use layers, retouchers can modify the color and tone based on how much shadow and highlights need to be shown. Each color channel can also be edited independently and merged back into one full color image.
There is another application of this method that can be used by raster graphics editing software. Each channel holds information about the original image that can be edited. The RED channel provides the contrast map which is great for colorists to work with the tone and gradients of the image. The GREEN channel contain the most detail of the source image so if a retoucher wants to delve into those specific parts of the image (e.g. skin blemishes, beauty marks, hair appearance, pores, etc.) this is the channel to work with. Finally, the BLUE channel is responsible for adjusting the noise in the image, so retouchers can work with this channel to get a smoother finish or adjust how grainy they want the image to look.
For example, we can apply a noise reduction filter to the BLUE channel “VTP_2759_B.jpg” without affecting the detail contained in the other channels. This is a way to isolate certain parts of the image where you can edit one without affecting the other. That way you can isolate specific retouching work through the use of channel separation by splitting channels.
After editing the grayscale channel images the raster graphics editing software can merge it back into a full color image at high resolution. The image has surely changed, so make a backup of the original image always in order to have the original source in case something goes wrong.
For this example I made some changes on the RED channel by adjusting brightness levels to give some contrast to the light while adjusting the curves in the GREEN channel. I left the BLUE channel alone since I wanted to preserve a more natural look and not too much smoothing or else I risk getting a “plastic” appearance on the skin. The result of that image is shown below.
Notice that editing contrast in the skin added more saturation in color while the details were further highlighted. It now has a much “warmer” appearance than before.
Splitting channels is a great way to edit in order to preserve the characteristics of one channel, while only working with the one you need. That way when you want to adjust something it will not affect the other channels.
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