Focal Pointe Observatory
Astrophotography by Bob Franke

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About How Much Color and Luminance


Image 1

Image 2

Image 3

Image 4







Here is an experiment about how the amount of color data affects the final LRGB image.


Processing Notes

  • All processing was done with CCDStack.

  • The Luminance was acquired at 0.64 arcsec/pixel and the color was binned 2x2. The above LRGB shots are displayed at 200%, or 0.32 arcsec/pixel.

  • The sub exposures, all at 15-minutes, were first normalized and sorted by weight.  For luminance, I used the middle 30 and 15 subs.  For color, the middle 15 and 7 were used.

  • The final images were mean combined, all using identical data rejection.  For the luminance, min/max clipping was used and STD sigma reject for the color.

  • DDP and color saturation adjustments were applied using... "apply to all."


  • In the first two images, the color data with seven subs, clearly has more noise.  The higher count of hot pixels shows that data rejection works better with more sub exposures.

  • Images two and three show how inadequate color can ruin your smooth luminance background.  The luminance of image three is smoother. However, the noisier color data has taken over.  Image two, with only 15 luminance subs, actually looks better.  This may be improved with selective smoothing of the color data.

  • Images three and four also show how insufficient color can ruin the your hard work in obtaining many luminance sub-exposures.  Image four is smoother and the color extends down to fainter stars.


  • When binning color, for each two hours of luminance try collecting one hour for each color channel.

  • Take enough sub-exposures so that rejection is effective.

  • Experiment with asymmetrical Min/Max clipping.  It may be better to clip more on the bottom or top.

  • If you are not fortunate to have reliably clear skies, images two and three may show a good way to go.  It can be useful to cut back on the luminance exposures and concentrate more on the  color.