HaRGB Process - (L+Ha)(R+Ha)GB

hrgbproc.jpg (58614 bytes)

Full Size Example


1 Use 1x1 for the RGB channels. Higher binning has a tendency to saturate the stars more easily resulting  in a loss of star color.
2 Use the minimum exposure time for RGB. Stan Moore was a big help with his SBIG discussion defining the optimum exposure time of sky level to 10x the readout noise.  For my ST-10 and this location that is a sky background level of about 300 ADU or 10 mins blue.
3 2X upsample the RGB and Ha images and use RegiStar for all image combining. For the RGB channels, use "calibrate" to equalization the background before Median combining.
4 Keep the images in the upsampled size for all remaining processing.
5 I use MaxIM to do a simple RGB combine with equalized background. I then find a bright star closest to G2 to set the white point.   Do not use DDP or any other sharpening/stretching tools.
6 Work in Photoshop 16bit RGB space to compress the histograms into the visible working space initially using levels and then switch to curves as the nebula areas just become visible.
7 Do the same for the Ha image
8 Switch mode to 8bit (must do this to do next step)
9 Extract the Red channel as a B/W image and combined with the Ha at aprox 50%.   You may need to make a few curves adjustments to make sure that the stars do not become too small.
10 After obtaining a good looking RGB image. Do a 2 to 3 pixel Median blur on the three channels. (This is another reason to use 1x1 binning since the median blurring will reduce the color channel resolution to about the same as 2x2 binning but with smoother color)
11 Create a new layer in the RGB image. Copy the Ha image into this layer, set to luminosity and level at 50%
12 Select the RGB layer and increase saturation. Some additional curves adjustment may be necessary in both Ha and RGB layers.


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