I worked out a method for aligning individual red, green and blue images and then creating single RGB image in Photoshop CS6 when I was processing my comet picture yesterday – there is probably a better one – so if you know it please send it to me!
(1) Load up the 3 individual colour images into CS6
(2) Copy the green and blue images onto the red image as new layers (for each image – select all then copy on image then click on red image, create new layer, then highlight layer name and then click <paste>)
(3) Change the transparency on each of green and blue layers to 50%
(4) Switch off green layer
(5) Click <move> and move blue layer until feature (comet, moon, etc.) is aligned with red layer.
(6) Switch off blue layer and switch on green layer.
(7) Click <move> and move green layer until feature (comet, moon, etc.) is aligned with red layer.
(8) Now all three layers are aligned
(9) Ensure all 3 layers switched on
(10) Select top layer – now crop the image to remove excess borders – this will automatically crop the other 2 layers as well.
(11) Save you Photoshop file as Photoshop proprietary format.
(12) Duplicate this file – so three copies – call then red, green, blue.
(13) In turn, load up each copy into CS6 and delete 2 layers so that the only layer that remains on each copy is the one that matches the name – e.g. the file labelled “red” only contains the red layer. Then select that layer, right click and flatten image for each file. Finally, save as TIFF file. This means you now have three aligned and cropped TIFF files – “red”, “green”, “blue”.
(14) In Photoshop, use Nol’s actions to create RGB file – works well.