IMPROVING COLOUR SATURATION AND REDUCING COLOUR NOISE.

Improving Colour Saturation.

The simplest but least satisfactory way of improving colour saturation in an image is to use Photoshop's Hue/Saturation option. While this is an effective method of boosting colour saturation it also magnifies any colour noise that exists. Photoshop offers a much more eloquent alternative.

The above image can use an increase in colour saturation. To increase saturation without adding to the colour noise which is inherent in the image, we must first convert the RGB image to Lab colour. Go to Image -> Mode -> Lab colour in the menu.

Open up the Lab channel.

We will increase the contrast in the "a" and "b" channels. Click on the "a" channel  and go to Image -> Adjustments-> Brightness/Contrast. Increase the contrast by 20 units.

Hit OK and repeat for the "b" channel using the same contrast value. If the saturation is satisfactory reconvert the image back to RGB by using Image -> Mode-> RGB colour. Save the image.

Reducing Colour Noise.

As astroimagers are chasing fainter objects, it is becoming increasingly harder to produce colour noise free images. Long RGB exposures and blurring the RGB images prior to combining with high S/N luminance images is used for fighting colour noise. This may not be effective if the object or parts of the object being imaged is barely brighter than the sky background.

The situation is even worse for DSLR owners.

Noise reduction processes on a final image will reduce fine detail and effect image sharpness. There is however a very simple and effective procedure in Photoshop that allows colour noise to be tackled without compromising detail.

The image clearly shows noise despite lengthy luminance and RGB imaging times. We will open up the RGB channels and perform a noise reduction procedure on the Red, Green, and Blue channels.

Click on the Red channel and go to Filter-> Noise-> Reduce noise in the menu.

Adjust the settings as shown in the above image and hit OK. Perform noise reduction with the same settings on the Green and Blue channels. No reduction is applied to the RGB channel.

Noise has been reduced in the right hand image without effecting detail.