A few posts back, I showed a narrowband image of IC 1805 – The Heart Nebula taken during the full Moon. It looked rather pink as the H-Alpha signal is so dominant and overpowers any greens and blues that the OIII signal might provide. Here’s a new, differently processed, version (note: I’ve also flipped it so that the heart is the right way up!). Read below to find out what I did differently.
Using the amazing PixInsight software, I split the R, G and B channels apart. This meant that the resulting red channel contained just the H-alpha signal, but the green and blue channels shared the signal from the OIII emissions. I then made a new O channel by combining the green and blue channels using a formula of (2*G + B)/3 which gave a bias towards the better image I saw in the green.
Calling the red ‘H’ and the new combine green and blue ‘O’, I stretched their histograms, but also used a range mask on the O to stretch it much more (the mask prevented the background from becoming too noisy). This was the key to getting more blue in the resulting image. Then I recombined using HHOO to correspond to LRGB. Now you know why these are called false colour images!. However, all the data is real, it’s just a personal preference.
I think the result has a more 3D effect.