LRGB processing

Before LRGB processing, taking deep sky quality color images was very difficult:

  • As only a portion of the spectral range is passed through each R G B filters, individual color exposure times had to be multiplied by about 4.
  • Typically, to get the same quality as a 30 minutes black & white image, one had to take 3x120 minutes exposures!

With LRGB, only the black & white (Luminosity) image should be good. The individual R G B images can be low definition (high CCD binning). Using CCD binning allows to lower the R G B exposure times.

You may think of LRGB as "color painting" a black & white image.

Now the question is "what's the limit?". The answer is very surprising:
You may bin the color components up to 8:8 with acceptable effects on the final image!

Following is the demonstration:

Let's start from a known color image (some flowers in my garden)

By bringing the color saturation to zero, the black & white (L) image is extracted


R G B components are extracted from the original image and reduced times 8
(yes, that's the actual size!)

By resizing x8 the above R G B images and combining them we obtain the RGB image (without L), not very good as can be expected...

Using LRGB processing, this is the reconstructed image, very close to the original. You will notice the "painting" effect on the overexposed area of the top flower.

As a conclusion, when color imaging deep sky, use the maximum available binning from the CCD camera for the R G B images. Also, applying a small smoothing filter on the R G B images should not hurt as it is better to loose on color definition than to bring noise from the R G B components.