This is my own attempt to remove the background gradient from my Heart Nebula image using Roger’s processing technique.
Results of stacking in Nebulosity (image used for process below):
Cropping the above image:
Applying masks – as per Roger’s technique:
The above image is close to final image, but I have added further layer with masks:
(i) General mask through most of central region but leaving another blurred background as per Roger’s technique just at edges where green slipped through. Central areas masked with 100% opacity 500 sized eraser.
(ii) Towards edge used 40% opacity initially with large 50 sized eraser.
(iii) Very close to edge used 40% opacity size 10 erazer to bring out missing stars without bringing back too much green background.
(iv) Finally, apply slight crop to remove very small part of edge around image where I haven’t been too successful!
Roger Samworth, who developed this technique, produced his own further version of my picture above which he feels brings out more of the nebulosity:
I think the above image has too much blue glow so I re-processed my image again by creating 2nd layer, tweaking red curve on top layer and using eraser around edge as well on this layer to stop the tweaked red from increasing red level of surrounding stars – my new version emphasising red below: