Hi, Luca: I see one issue with the flow you described. The stars do have RGB colors and won't spill outside of ha stars. But the size of stars are also limited by ha stars, which is very small. After combination, stars are hardly seen. Is there a good way to grow or increase size of ha stars?
Wei
Wei,
You are correct. If you look at my recent Bubble Nebula image you can see exactly the point you are raising.
Versions D and F differ by how much the stars are stretched. I originally kept the stars very tight and barely stretched beyond the initial histogram transformation. I liked the way the image was almost starless but not quite. In discussions with a few other imagers, the balance of stars size with the rest of the composition was raised and I simply went back and stretched bit more the star luminance layer, extending the footprint of the stars. RGB star color filled the expanded stars nicely. Ultimately, I went back to the small star version because for this image I like it better but the method offers the flexibility. Also, if the RGB stars end up being too small, one can use the maximum filter in the RGB color star layer to extend the color radially.
An alternative workflow is to add the RGB stars (not just their color) with Screen blending mode and balance the narrowband and RGB stars. I find that it is more difficult to keep a natural look with this approach because the RGB background also blends in unless it's masked out, and that's always tough to achieve perfectly especially near bright stars.
