Using Desaturation to Avoid RGB Problems

One day you will probably find yourself faced with having to use an image that has not only been provided by the client in RGB mode but is filled with what are obviously bright RGB colors.

If you try changing the mode to CMYK, all these RGB colors will immediately become their “closest” CMYK equivalent, which might, of course, not look anything like the original. That is because in order to find the appropriate CMYK color, Photoshop simply reverses the polarity of the percentages of RGB and renders those values as the new CMY(K) shade. So, if the RGB color was made up of red and green completely off and blue completely on, it becomes instead a CMY color made up of C and M (almost) completely on and Y completely off. The result is that on screen the color turns from being an intense, glowing blue to being a dark, bluish-purple. Nevertheless, as far as Photoshop is concerned, it has done a good job with the conversion.

If your image contains a mix of colors that are both inside and outside the CMYK range, and only those colors outside it change when you convert the image, it can lead to a very unbalanced result.

To avoid this, do not make the color-mode conversion immediately. While the image is still in RGB mode, choose Image > Adjustments > Hue & Saturation, and then gently reduce the saturation level. As you do so, you are pulling all the RGB colors in the image back toward the CMYK range. The image is adjusted holistically because you are working on everything at once, and this means your image maintains the overall balance it had to begin with. Best of all, you get to decide where you want the process to stop, which is how you should approach all your image adjustments.

	If you only want to desaturate certain ranges of color in your image, try selecting them by using Select > Color Range. This method can give much better and more convincing results than by using the Magic Wand tool.